Orca-Cad: port SnapOrca Design (parametric CAD tab) onto mainline OrcaSlicer

Grafts the sketch-first CAD environment from snaporca-cad onto the mainline OrcaSlicer/OrcaSlicer base (vs snaporca's Snapmaker/OrcaSlicer base): - 133 new files: CadDocument/SketchEngine/GeometryEngine/SketchConstraints/ SketchSolver/SketchInference/ThreadStandards + vendored libslvs solver; DesignPanel/DesignCanvas/DesignSketchTool/SketchInlineEditor GUI; GLGizmo Primitive/Sketch; 75 design icons; Catch2 tests. - Integration hooks ported to mainline's diverged versions: Design tab in MainFrame, embedded design viewport + sketch overlay + per-canvas chrome suppression in GLCanvas3D/PartPlate, gizmo registration, Plater accessors, CMake wiring (libslvs subdir, CAD sources, OCCT ModelingAlgorithms=ON). Structural integration complete; build verification pending. Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com> Claude-Session: https://claude.ai/code/session_01BVzKmX6Y1aEteit1HTXG4Q
2026-09-18 14:32:36 +00:00 · 2026-06-28 12:40:38 +02:00
parent 449a4cf9fc
commit 0f4060c0a9
146 changed files with 34845 additions and 17 deletions
@@ -28,7 +28,7 @@ orcaslicer_add_cmake_project(OCCT
        #-DBUILD_MODULE_DataExchange=OFF
        -DBUILD_MODULE_Draw=OFF
        -DBUILD_MODULE_FoundationClasses=OFF
-        -DBUILD_MODULE_ModelingAlgorithms=OFF
+        -DBUILD_MODULE_ModelingAlgorithms=ON
        -DBUILD_MODULE_ModelingData=OFF
        -DBUILD_MODULE_Visualization=OFF
 )
@@ -0,0 +1,58 @@
+# Design (CAD) tab — upstream portability assessment
+
+**Question:** can the SnapOrca *Design tab* (sketch-first parametric CAD: sketch →
+constrain → extrude/revolve/fillet/hole/thread/shell, multi-body, undo) be contributed
+to **mainline OrcaSlicer** (2.4 dev) rather than living only in this Snapmaker fork?
+
+**Short answer: yes, technically clean — the feature is self-contained and vendor-neutral.
+The single real gatekeeper is whether upstream is willing to take on OpenCASCADE (OCCT) as a
+build dependency, i.e. whether OrcaSlicer wants to become a CAD-integrated slicer.**
+
+## Why it is portable
+
+- **Self-contained.** The feature is ~28 kLOC of *new* files (kernel
+  `CadDocument` / `SketchEngine` / `GeometryEngine` / `Sketch*`; GUI
+  `DesignPanel` / `DesignCanvas` / `DesignSketchTool` / `GLGizmoSketch`) plus a
+  vendored, self-contained SolveSpace solver (`src/libslic3r/slvs/`, ~10 kLOC, LGPL).
+- **Tiny, guarded injection into shared code (~2–3 % surface).** The only edits to
+  pre-existing OrcaSlicer files are: a `m_design_sketch_tool` member + a handful of
+  null-checked hooks in `GLCanvas3D` (render overlay, mouse routing, Delete/Esc/Ctrl+Z),
+  a tab member + construction in `MainFrame`, and a few forward declarations. **No
+  changes** to the slicing pipeline (Print/PrintObject/Layer/GCode), Plater, Tab, Model,
+  or the printer-profile/config system.
+- **Zero Snapmaker coupling.** No "Snapmaker" references in any Design/CAD file; icons
+  are generic `resources/images/design_*.svg`; the code is pure wxWidgets/OpenGL/OCCT.
+  It would build and run in any OrcaSlicer fork unchanged.
+- **Orthogonal git history.** The feature lives on `feature/cad-primitives` as a clean,
+  linear series of `Design:` / `C*` / `M*` commits with no interleaved fork-specific
+  work, so it cherry-picks onto a clean OrcaSlicer base without slicing-logic conflicts.
+
+## The real blocker: OCCT
+
+`src/libslic3r/CMakeLists.txt` links ~30 OCCT toolkits (`TKBRep TKFillet TKOffset
+TKBool TKPrim TKTopAlgo TKMath TKernel …`) via `find_package(OpenCASCADE REQUIRED)`.
+OCCT is large (hundreds of MB of binaries, +15–30 min to a clean deps build) and is a
+dependency **mainline OrcaSlicer has never carried**. Accepting it is an architectural
+decision about the project's scope, not a code problem.
+
+## Top work items to upstream (≈3–5 dev-days)
+
+1. **Make OCCT an *optional* dependency.** Add it to `deps/` like the other externals,
+   gate the whole feature behind a CMake option (`-DENABLE_DESIGN_CAD=OFF` by default),
+   and document OCCT install per-platform. Builds without OCCT simply omit the tab.
+2. **Guard the tab construction** in `MainFrame` (and the `GLCanvas3D` hooks) on that
+   same flag so a minimal build links and runs with no Design code at all.
+3. **Tests + docs + license hygiene.** Add regression coverage for the kernel
+   (sketch-solve, extrude, fillet, undo), ship the LGPL notice for the vendored
+   `slvs/`, and add user docs. (libslvs itself is self-contained, no external deps.)
+
+## Verdict
+
+Portability is **high (≈7/10): "needs moderate adaptation," not "deeply entangled."**
+The engineering to upstream is modest and mechanical (optional-dependency plumbing +
+tests/docs). The decision is strategic: **does OrcaSlicer want OCCT and a CAD tab?** If
+yes, this feature is a near-drop-in starting point.
+
+---
+*Generated 2026-06-21 from a read-only analysis of the `feature/cad-primitives` branch.
+Tracking issue: bd `snaporca-frp`.*
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+<svg xmlns="http://www.w3.org/2000/svg" width="40" height="40" viewBox="0 0 40 40">
+  <!-- Pencil body -->
+  <path d="M28.5 6.5l5 5L14 31l-5.5 1.5L10 27 28.5 6.5z" style="fill:#009688"/>
+  <!-- Pencil tip (dark) -->
+  <path d="M8.5 28.5l1.5 1.5 4.5-1L28.5 15l-3.5-3.5L8.5 28z" style="fill:#2b3436"/>
+  <!-- Pencil line -->
+  <line x1="10" y1="26" x2="25" y2="11" stroke="#2b3436" stroke-width="2"/>
+</svg>
@@ -0,0 +1,8 @@
+<svg xmlns="http://www.w3.org/2000/svg" width="40" height="40" viewBox="0 0 40 40">
+  <!-- Pencil body (dark mode colors) -->
+  <path d="M28.5 6.5l5 5L14 31l-5.5 1.5L10 27 28.5 6.5z" style="fill:#4db6ac"/>
+  <!-- Pencil tip -->
+  <path d="M8.5 28.5l1.5 1.5 4.5-1L28.5 15l-3.5-3.5L8.5 28z" style="fill:#e0e0e0"/>
+  <!-- Pencil line -->
+  <line x1="10" y1="26" x2="25" y2="11" stroke="#e0e0e0" stroke-width="2"/>
+</svg>
@@ -0,0 +1,70 @@
+# Deps-only base image for fast iteration on SnapOrca.
+# Identical system+pinned-dependency setup to scripts/Dockerfile, but STOPS after
+# `build_linux.sh -dr` (no slicer/AppImage build). Produces an image with the pinned
+# deps baked at /OrcaSlicer/deps/build/destdir, so the slicer can be rebuilt
+# incrementally via scripts/docker-iter-build.sh without re-running the long deps build.
+#
+# Build once (rebuild only when deps/ changes, e.g. OCCT module flags):
+#   docker build -t snaporca-deps -f scripts/Dockerfile.deps .
+FROM docker.io/ubuntu:24.04
+LABEL maintainer="SnapOrca CAD iteration base"
+
+# Disable interactive package configuration
+RUN apt-get update && \
+    echo 'debconf debconf/frontend select Noninteractive' | debconf-set-selections
+
+# Add a deb-src
+RUN echo deb-src http://archive.ubuntu.com/ubuntu \
+    $(cat /etc/*release | grep VERSION_CODENAME | cut -d= -f2) main universe>> /etc/apt/sources.list
+
+RUN apt-get update && apt-get install  -y \
+    autoconf \
+    build-essential \
+    cmake \
+    curl \
+    eglexternalplatform-dev \
+    extra-cmake-modules \
+    file \
+    git \
+    gstreamer1.0-plugins-bad \
+    gstreamer1.0-libav \
+    libcairo2-dev \
+    libcurl4-openssl-dev \
+    libdbus-1-dev \
+    libglew-dev \
+    libglu1-mesa-dev \
+    libgstreamer1.0-dev \
+    libgstreamerd-3-dev \
+    libgstreamer-plugins-base1.0-dev \
+    libgstreamer-plugins-good1.0-dev \
+    libgtk-3-dev \
+    libsecret-1-dev \
+    libsoup2.4-dev \
+    libssl3 \
+    libssl-dev \
+    libtool \
+    libudev-dev \
+    libwayland-dev \
+    libwebkit2gtk-4.1-dev \
+    libxkbcommon-dev \
+    locales \
+    locales-all \
+    m4 \
+    pkgconf \
+    sudo \
+    wayland-protocols \
+    wget
+
+ENV LC_ALL=en_US.utf8
+RUN locale-gen $LC_ALL
+ENV SSL_CERT_FILE=/etc/ssl/certs/ca-certificates.crt
+
+COPY ./ OrcaSlicer
+WORKDIR OrcaSlicer
+
+# System dependencies
+RUN ./build_linux.sh -u
+
+# Pinned dependencies in ./deps (OCCT 7.6 with ModelingAlgorithms enabled, OpenCV,
+# OpenVDB, Boost, wxWidgets, ...). This is the long step; it is baked into the image.
+RUN ./build_linux.sh -dr
@@ -0,0 +1,35 @@
+#!/usr/bin/env bash
+# Incremental slicer build against the snaporca-deps base image.
+#
+# The deps-baked image (built from scripts/Dockerfile.deps) carries the pinned
+# dependencies at /OrcaSlicer/deps/build/destdir. This script mounts the LIVE source
+# tree and resources over the baked copy so code/CMake edits apply immediately, and
+# persists /OrcaSlicer/build in a named volume so ninja recompiles only what changed.
+#
+# Result: edit -> rebuild in seconds-to-minutes instead of a full Docker rebuild.
+#
+# Usage (run on the build host, e.g. behemoth, from anywhere):
+#   scripts/docker-iter-build.sh
+#   IMAGE=snaporca-deps scripts/docker-iter-build.sh
+#
+# On success the binary is inside the persistent volume at
+# /OrcaSlicer/build/package/bin/snapmaker-orca (copy it out with a follow-up
+# `docker run --rm -v snaporca_buildcache:/b alpine cp ...` or via this script's tail).
+set -euo pipefail
+
+REPO="$(cd "$(dirname "${BASH_SOURCE[0]}")/.." && pwd)"
+IMAGE="${IMAGE:-snaporca-deps}"
+BUILD_VOL="${BUILD_VOL:-snaporca_buildcache}"
+
+echo "REPO=$REPO  IMAGE=$IMAGE  BUILD_VOL=$BUILD_VOL"
+
+docker run --rm \
+  -v "$REPO/src":/OrcaSlicer/src \
+  -v "$REPO/resources":/OrcaSlicer/resources \
+  -v "$BUILD_VOL":/OrcaSlicer/build \
+  "$IMAGE" \
+  bash -lc 'cd /OrcaSlicer && ./build_linux.sh -sr'
+
+echo "=== build finished; checking for binary ==="
+docker run --rm -v "$BUILD_VOL":/b "$IMAGE" \
+  bash -lc 'ls -lh /b/package/bin/snapmaker-orca 2>/dev/null && file /b/package/bin/snapmaker-orca || echo "NO BINARY"'
@@ -20,6 +20,9 @@ endif()

 option(BUILD_SHARED_LIBS "Build shared libs" OFF)

+# Vendored SolveSpace constraint solver (2D sketch solver backbone).
+add_subdirectory(slvs)
+
 set(lisbslic3r_sources
    AABBMesh.cpp
    AABBMesh.hpp
@@ -275,6 +278,8 @@ set(lisbslic3r_sources
    Geometry/VoronoiUtils.cpp
    Geometry/VoronoiUtils.hpp
    Geometry/VoronoiVisualUtils.hpp
+    GeometryEngine.cpp
+    GeometryEngine.hpp
    Int128.hpp
    KDTreeIndirect.hpp
    Layer.cpp
@@ -385,6 +390,20 @@ set(lisbslic3r_sources
    SLA/JobController.hpp
    SLA/Pad.cpp
    SLA/Pad.hpp
+    SketchEngine.cpp
+    SketchEngine.hpp
+    SketchConstraints.cpp
+    SketchConstraints.hpp
+    SketchSolver.cpp
+    SketchSolver.hpp
+    SketchInference.cpp
+    SketchInference.hpp
+    SketchImport.cpp
+    SketchImport.hpp
+    CadDocument.cpp
+    CadDocument.hpp
+    ThreadStandards.cpp
+    ThreadStandards.hpp
    SLAPrint.cpp
    SLAPrint.hpp
    SLAPrintSteps.cpp
@@ -546,6 +565,9 @@ find_package(JPEG REQUIRED)
 find_package(draco REQUIRED)

 set(OCCT_LIBS
+    TKFillet
+    TKOffset
+    TKBool
    TKXDESTEP
    TKSTEP
    TKSTEP209
@@ -591,6 +613,7 @@ target_link_libraries(libslic3r
        clipper
        Clipper2
        draco::draco
+        libslvs
        glu-libtess
        JPEG::JPEG
        libslic3r_cgal
@@ -0,0 +1,355 @@
+#ifndef slic3r_CadDocument_hpp_
+#define slic3r_CadDocument_hpp_
+
+#include "TriangleMesh.hpp"
+#include "SketchEngine.hpp"
+#include "GeometryEngine.hpp"   // FaceGroup
+#include "Color.hpp"            // ColorRGBA (per-body display colour override)
+
+#include <TopoDS_Shape.hxx>
+#include <TopoDS_Wire.hxx>
+#include <string>
+#include <vector>
+#include <utility>
+
+namespace Slic3r {
+
+enum class CadFeatureType { Sketch, Extrude, Fillet, Chamfer, Hole, Thread, Shell, Revolve, Sweep, Pattern, Plane, Loft, Draft, Import, Boolean, Cut };
+enum class SketchShape    { Rectangle, Circle };
+enum class BooleanMode    { New, Add, Cut, Intersect };
+
+enum class ExtrudeEnd { Blind, Symmetric, TwoSided, ThroughAll, UpToFace, UpToVertex };
+
+struct CadFeature {
+    CadFeatureType type{CadFeatureType::Sketch};
+    std::string    name;
+    bool           enabled{true};
+
+    // Sketch params (centered on the plane origin)
+    SketchShape shape{SketchShape::Rectangle};
+    SketchPlane plane{SketchPlane::XY()};
+    double      width{20};
+    double      height{20};
+    double      radius{10};
+
+    // Real 2D sketch geometry (Onshape-style). When non-empty this takes
+    // precedence over the shape/width/height/radius enum path in build_sketch_wire.
+    SketchProfile profile;
+
+    // Onshape-style multi-entity sketch geometry. When non-empty this takes
+    // precedence over both `profile` and the shape-enum path in build_sketch_wire.
+    std::vector<SketchEntity> entities;
+
+    // 2D geometric constraints on `profile` (point indices). Solved in place.
+    std::vector<SketchConstraintDef> constraints;
+
+    // Onshape-style constraints on `entities` (Fase 4.2). Solved in place against
+    // entity endpoints. Used when `entities` is non-empty (the legacy `constraints`
+    // vector applies only to the `profile` path).
+    std::vector<SketchEntityConstraintDef> entity_constraints;
+
+    // Imported rigid 2D art (Text glyphs / SVG vector paths) as filled regions.
+    // Each region: contour[0] = outer loop, contour[1..] = holes; points in
+    // plane (u,v) millimetres. Rendered as a sketch overlay and extruded via a
+    // faces-with-holes path (SketchEngine::make_extrude_regions) — deliberately
+    // NOT solver entities, so imported art contributes zero DoF and never
+    // pollutes the constraint solver / DoF readout. When non-empty it takes
+    // precedence over the entities/profile/shape paths in the Extrude case.
+    std::vector<std::vector<std::vector<Vec2d>>> imported_regions;
+
+    // Imported rigid 3D B-rep solid (STEP). When the feature type is Import this carries
+    // the OCCT shape verbatim — it is adopted as a base body in route_feature (no parametric
+    // recipe). Downstream face/edge features (fillet/chamfer/cut/shell/...) act on it like any
+    // other body. TopoDS_Shape is a cheap handle, so copying it through recompute/checkpoint
+    // snapshots is cheap. In-session only for now (no BRep serialization yet).
+    TopoDS_Shape imported_solid;
+
+    // Non-destructive placement transform for imported_regions (Text/SVG),
+    // applied at display + extrude time as
+    //   p -> (p.x*import_scale_x + import_offset.x, p.y*import_scale_y + import_offset.y).
+    // Lets the art be moved / enlarged / stretched (independent X/Y) repeatedly
+    // without re-vectorising. Identity = no change.
+    Vec2d  import_offset{0, 0};
+    double import_scale_x{1.0};
+    double import_scale_y{1.0};
+    // Text/SVG dropped ONTO a solid face (centred on it): the extrude then defaults to an
+    // inward Cut (engraving) targeting `import_face_body`. False = free art on a plane.
+    bool   import_on_face{false};
+    int    import_face_body{-1};
+
+    // Extrude params
+    int         sketch_ref{-1};   // index into features[] of the consumed sketch
+    double      distance{10};
+    bool        symmetric{false};
+    BooleanMode mode{BooleanMode::New};
+    ExtrudeEnd  extrude_end{ExtrudeEnd::Blind};
+    double      distance2{0};     // second-side depth for TwoSided
+    double      taper_deg{0};     // draft angle (C4-part2)
+    bool        flip{false};      // reverse the extrude direction (negate plane normal)
+    int         up_to_face{-1};   // target solid-face id for UpToFace (C4-part2)
+    int         extrude_src_face{-1}; // global face id on the current body to extrude as a profile; -1 = use sketch wire
+    Vec3d       up_to_point{0,0,0}; // target for UpToVertex (C4-part2)
+    // Multi-body target: which body (index into CadDocument::bodies) this feature acts on.
+    // -1 = auto (last body). A New extrude appends a fresh body; Add/Cut/Intersect, dress-up,
+    // hole and face-extrude(non-New) mutate bodies[target]; face-extrude reads its source
+    // face from bodies[target] too. The source-face owner for face-extrude lives here.
+    int         target_body{-1};
+
+    // Dress-up params (Fillet/Chamfer) — applied to the current body in order
+    double      dressup_size{1.0};         // fillet radius or chamfer distance
+    FaceGroup   face_group{FaceGroup::All};
+    int         dressup_edge{-1};          // global edge id for edge-targeted fillet/chamfer; -1 = use face_group
+
+    // Hole params (positioned circular cut into the current body)
+    double      hole_diameter{5};
+    double      hole_depth{10};
+    bool        hole_through{true};        // true = symmetric through-cut, ignores hole_depth
+    double      hole_x{0};                 // position on the plane (plane u/x axis)
+    double      hole_y{0};                 // position on the plane (plane v/y axis)
+
+    // Thread params (helical thread about the plane normal at a positioned point)
+    double      thread_radius{5};          // nominal cylinder radius
+    double      thread_pitch{2};           // axial advance per turn
+    double      thread_height{10};         // total axial length
+    double      thread_depth{1};           // radial crest depth of the thread profile
+    bool        thread_internal{false};    // false = external threaded rod (New body);
+                                           // true = tapped bore cut into the current body
+    double      thread_x{0};               // axis position on the plane (u/x axis)
+    double      thread_y{0};               // axis position on the plane (v/y axis)
+
+    // Shell params (hollow the current body to a wall thickness, removing one open face)
+    double      shell_thickness{2};        // wall thickness (inward offset)
+    int         shell_face{-1};            // global face id to remove (open the shell); -1 = none
+
+    // Draft params (taper a single solid face about a neutral plane = body bbox bottom, pull +Z)
+    int         draft_face{-1};            // global face id to draft; -1 = none
+    double      draft_angle{5};            // draft angle in degrees (signed: + leans the face inward)
+
+    // Revolve params (sweep a profile about an in-plane axis through the plane origin).
+    // Reuses sketch_ref / entities (profile), flip (direction), mode (boolean) and
+    // target_body. revolve_axis: 0 = plane X axis, 1 = plane Y axis.
+    double      revolve_angle{360};        // sweep angle in degrees (1..360)
+    int         revolve_axis{0};           // 0 = plane X, 1 = plane Y
+
+    // Sweep: profile carried by sketch_ref / entities (like Extrude); the spine is a
+    // second Sketch referenced by sweep_path_ref (an open or closed wire). Reuses
+    // mode (boolean) and target_body.
+    int         sweep_path_ref{-1};        // index into features[] of the path Sketch
+
+    // Loft: build a solid through 2+ closed profile Sketches (loft_profile_refs, in
+    // order, each on its own plane). loft_ruled=false → smooth sections, true → ruled.
+    // Reuses mode (boolean) and target_body.
+    std::vector<int> loft_profile_refs;    // ordered indices into features[] of profile Sketches
+    bool        loft_ruled{false};
+
+    // Pattern: replicate the target body, copies fused into it. pattern_circular=false
+    // → linear (pattern_count instances spaced pattern_spacing along plane axis
+    // pattern_dir: 0=X, 1=Y); true → circular (pattern_count instances over
+    // pattern_angle° total about the plane normal through the plane origin, so a seed
+    // offset from the origin orbits the axis). Reuses target_body + plane.
+    bool        pattern_circular{false};
+    int         pattern_count{3};          // total instances incl. the seed (>=1)
+    double      pattern_spacing{20};       // linear step (mm)
+    int         pattern_dir{0};            // linear direction: 0 = plane X, 1 = plane Y
+    double      pattern_angle{360};        // circular total angle (degrees)
+
+    // Datum/reference plane: a derived SketchPlane the document offers as a selectable
+    // sketch plane (no solid). plane_base selects the reference (0=XY,1=XZ,2=YZ, or 3+N
+    // = the Nth earlier datum plane); plane_offset shifts along the base normal;
+    // plane_angle tilts plane_angle° about the base axis plane_axis (0=base X, 1=base Y).
+    int         plane_base{0};
+    double      plane_offset{20};
+    double      plane_angle_tilt{0};       // degrees (named *_tilt to avoid clash w/ revolve)
+    int         plane_axis{0};             // tilt axis: 0 = base X, 1 = base Y
+
+    // Boolean: combine two EXISTING bodies. `mode` reuses BooleanMode (Add = union,
+    // Cut = subtract tool from target, Intersect = keep overlap; New unused). `target_body`
+    // is the body that survives (result written back to it); `bool_tool_body` is the other
+    // operand, consumed (erased) unless `bool_keep_tool`. `bool_tolerance` = OCCT fuzzy value
+    // (0 = exact). Per-face merge: when both bool_target_face/bool_tool_face are set, the tool
+    // is first snapped so those two faces are coincident (gap closed within bool_tolerance),
+    // then the boolean welds them and coplanar faces are unified into one clean face.
+    int    bool_tool_body{-1};
+    bool   bool_keep_tool{false};
+    double bool_tolerance{0.0};
+    int    bool_target_face{-1};   // global face id on the target body to mate (-1 = none)
+    int    bool_tool_face{-1};     // global face id on the tool body to mate (-1 = none)
+
+    // Cut: split one target body with a plane, keeping the upper half, lower half, or both.
+    // Reuses `plane` for the cut plane and `target_body` for which body is cut.
+    double cut_offset{0.0};       // offset along the cut-plane normal (mm)
+    bool   cut_flip{false};       // flip the normal => swaps which side is "upper"
+    bool   cut_keep_upper{true};  // keep the +normal half
+    bool   cut_keep_lower{false}; // keep the -normal half (both => split into two bodies)
+};
+
+// One independent solid in a multi-body document.
+struct CadBody {
+    TopoDS_Shape shape;
+    std::string  name;
+    // Per-body display colour override (Color tool). When has_color is false the GUI
+    // falls back to the auto body-index palette. Carried across recompute() by body index.
+    bool         has_color{false};
+    ColorRGBA    color;
+};
+
+// OCCT-only feature tree backing the Design tab. No GUI dependencies (lives in libslic3r).
+class CadDocument {
+public:
+    std::vector<CadFeature> features;
+    // Multi-body result of the last replay. A "New" extrude appends a body; other ops
+    // mutate a target body. Empty after a failed/empty recompute.
+    std::vector<CadBody>    bodies;
+    TopoDS_Shape            body;          // compound of all bodies (1 body => that body) — display/compat
+    TriangleMesh            display_mesh;      // tessellation of all bodies, concatenated (picking)
+    std::vector<TriangleMesh> display_body_meshes; // one mesh per body, in `bodies` order (per-body color)
+    std::vector<int>        display_tri_face;  // per-triangle face id WITHIN its source body
+    std::vector<int>        display_tri_body;  // per-triangle source body index (into bodies)
+    std::string             error;             // last recompute error ("" = ok)
+
+    double linear_deflection{0.01};
+    double angular_deflection{0.5};
+
+    int  add_sketch(SketchShape shape, const SketchPlane& plane,
+                    double width, double height, double radius,
+                    const std::string& name);
+    int  add_sketch_profile(const SketchProfile& profile, const SketchPlane& plane,
+                            const std::string& name);
+    // Onshape-style multi-entity sketch: stores the entity list verbatim. When
+    // non-empty it takes precedence over profile/enum in build_sketch_wire.
+    int  add_sketch_entities(const std::vector<SketchEntity>& entities,
+                             const SketchPlane& plane, const std::string& name,
+                             const std::vector<SketchEntityConstraintDef>& constraints = {});
+    // Solve features[index]'s sketch constraints, writing solved coordinates back
+    // into its profile.points. No-op (returns true) if the feature has no
+    // constraints. Returns false if index is invalid / not a Sketch / solve fails.
+    bool solve_sketch_feature(int index);
+    int  add_extrude(int sketch_ref, double distance, bool symmetric,
+                     BooleanMode mode, const std::string& name);
+    // Extrude a single loop given directly as entities (sketch_ref = -1, plane carried).
+    int  add_extrude_entities(const std::vector<SketchEntity>& entities,
+                              const SketchPlane& plane, double distance, bool symmetric,
+                              BooleanMode mode, const std::string& name);
+    // Extrude an existing solid FACE (global face id on the body) as the profile.
+    int  add_extrude_face(int src_face, double distance, bool symmetric,
+                          BooleanMode mode, const std::string& name);
+    int  add_fillet(double radius, FaceGroup faces, const std::string& name);
+    int  add_fillet(double radius, int edge_id, const std::string& name);
+    int  add_chamfer(double distance, FaceGroup faces, const std::string& name);
+    int  add_chamfer(double distance, int edge_id, const std::string& name);
+    int  add_hole(double diameter, double depth, bool through,
+                  double x, double y, const SketchPlane& plane,
+                  const std::string& name);
+    int  add_thread(double radius, double pitch, double height, double depth,
+                    bool internal, double x, double y, const SketchPlane& plane,
+                    const std::string& name);
+    int  add_revolve(int sketch_ref, double angle, int axis, bool flip,
+                     BooleanMode mode, const std::string& name);
+    // Self-contained revolve of a single loop given directly as entities (sketch_ref=-1).
+    int  add_revolve_entities(const std::vector<SketchEntity>& entities,
+                              const SketchPlane& plane, double angle, int axis, bool flip,
+                              BooleanMode mode, const std::string& name);
+    // Sweep the profile Sketch (profile_sketch_ref) along the path Sketch (path_sketch_ref).
+    int  add_pattern(bool circular, int count, double spacing, int dir,
+                     double angle_deg, int target_body, const std::string& name);
+    int  add_sweep(int profile_sketch_ref, int path_sketch_ref, BooleanMode mode,
+                   const std::string& name);
+    // Loft through the ordered profile Sketches (each a closed wire on its own plane).
+    int  add_loft(const std::vector<int>& profile_refs, bool ruled, BooleanMode mode,
+                  const std::string& name);
+    int  add_shell(double thickness, int face, int target_body, const std::string& name);
+    int  add_draft(double angle, int face, int target_body, const std::string& name);
+    // Boolean between two existing bodies. op reuses BooleanMode (Add=union, Cut=subtract,
+    // Intersect=common; New invalid). target survives, tool is consumed unless keep_tool.
+    // tolerance = OCCT fuzzy value; target_face/tool_face (-1 = none) drive the per-face snap+merge.
+    int  add_boolean(BooleanMode op, int target_body, int tool_body, bool keep_tool,
+                     double tolerance, int target_face, int tool_face, const std::string& name);
+    // Plane Cut (Onshape split-by-plane): trim target_body by the plane (origin offset along
+    // its normal by `offset`, normal flipped iff `flip`). keep_upper/keep_lower select the
+    // +normal / -normal half; both => the body is split into two coexisting bodies.
+    int  add_cut(const SketchPlane& plane, double offset, bool flip,
+                 bool keep_upper, bool keep_lower, int target_body, const std::string& name);
+    // Datum plane: derived from base (0=XY/1=XZ/2=YZ/3+N=Nth earlier datum), offset
+    // along its normal, optional tilt about a base axis. Produces no solid.
+    int  add_plane(int base, double offset, double angle_tilt, int axis,
+                   const std::string& name);
+    // Every datum plane currently in the recipe, in feature order, as (name, plane).
+    // Used by the GUI to populate plane pickers (after the 3 base planes).
+    std::vector<std::pair<std::string, SketchPlane>> resolve_datum_planes() const;
+    void clear();
+    bool recompute();   // replay features -> body + display_mesh; false on error
+
+    // Undo/redo of the feature recipe (Onshape-style Ctrl+Z). The caller marks a
+    // user-action boundary by calling checkpoint() BEFORE the mutation(s) for that
+    // action (add/delete/move/replace, or a direct features edit). undo()/redo() then
+    // restore the snapshot and recompute(). Because everything else (bodies/meshes/
+    // body) is derived by recompute(), snapshotting `features` alone is a complete,
+    // exact history; one checkpoint == one Ctrl+Z step.
+    void checkpoint();   // snapshot `features` for undo + invalidate redo
+    bool can_undo() const { return !m_undo.empty(); }
+    bool can_redo() const { return !m_redo.empty(); }
+    size_t undo_depth() const { return m_undo.size(); }
+    size_t redo_depth() const { return m_redo.size(); }
+    bool undo();   // restore the previous feature list + recompute(); false if no history
+    bool redo();   // re-apply the most recently undone change; false if none
+
+    // Feature-tree editing (Onshape-style). All are transactional: they snapshot
+    // features, mutate, recompute(), and roll back to the snapshot (re-recomputing)
+    // if the result is invalid — so a failed edit never leaves a broken body.
+    //
+    // remove_feature: erase features[index]; deleting a Sketch cascades to the
+    //   Extrude(s) that consume it; surviving sketch_ref indices are remapped.
+    // move_feature:   shift features[index] by delta (-1 up / +1 down), clamped;
+    //   sketch_ref indices of the two swapped slots are remapped.
+    // replace_feature: overwrite features[index] with `edited` (its name and, for
+    //   an Extrude, its sketch_ref are preserved from the original).
+    bool remove_feature(int index);
+    bool move_feature(int index, int delta);
+    bool replace_feature(int index, const CadFeature& edited);
+    // replace_sketch_extrude: a box is two linked features (Sketch + Extrude);
+    //   overwrite both slots from one `edited` candidate (sketch params ->
+    //   features[sketch_idx], extrude params -> features[extrude_idx]), keeping
+    //   each slot's name/type and the sketch_ref link. Transactional like above.
+    bool replace_sketch_extrude(int sketch_idx, int extrude_idx, const CadFeature& edited);
+
+    // Apply ONE candidate feature on top of the current committed body and
+    // tessellate the result into out_mesh, WITHOUT modifying features/body/
+    // display_mesh. Returns false (with err set) if the candidate is invalid.
+    // Used by the Design tab to show a translucent ghost before Confirm.
+    bool preview(const CadFeature& candidate, TriangleMesh& out_mesh, std::string& err) const;
+    // Same, but also returns the per-body meshes (in `bodies` order; the candidate may append
+    // one), so the GUI can apply its display-only per-body Move transforms to the ghost and keep
+    // it overlaid on the moved body instead of floating back at the untransformed origin.
+    bool preview(const CadFeature& candidate, TriangleMesh& out_mesh,
+                 std::vector<TriangleMesh>& out_body_meshes, std::string& err) const;
+
+private:
+    TopoDS_Wire build_sketch_wire(const CadFeature& sketch) const;
+    // Apply a single feature to (result, have_body), throwing std::runtime_error on
+    // failure. `context` is the body whose faces/edges the feature reads (face-extrude
+    // source, up-to-face target, dress-up, hole) — it differs from `result` only when the
+    // feature builds a NEW body from an existing one (face-extrude New). Shared by route.
+    void apply_feature(TopoDS_Shape& result, bool& have_body,
+                       const TopoDS_Shape& context, const CadFeature& f) const;
+    // Route one feature into the bodies list: resolve its target body, decide whether it
+    // starts a new body (empty list, or an Extrude with mode New) vs mutates an existing
+    // one, then apply_feature. Shared by recompute() (replay all) and preview() (candidate).
+    void route_feature(std::vector<CadBody>& bodies, const CadFeature& f) const;
+    // Boolean between two existing bodies: resolve target + tool, optionally snap the tool so
+    // the picked faces mate, run the OCCT op (with fuzzy tolerance), write the result back to the
+    // target and erase the consumed tool. Mutates the bodies vector directly (unlike apply_feature,
+    // which works on a single result shape). Throws std::runtime_error on a failed op.
+    void apply_boolean(std::vector<CadBody>& bodies, const CadFeature& f) const;
+    void apply_cut(std::vector<CadBody>& bodies, const CadFeature& f) const;
+
+    // Undo/redo stacks of feature-list snapshots. checkpoint() pushes onto m_undo and
+    // clears m_redo; undo()/redo() shuffle the current state between them. Capped so a
+    // long session can't grow unbounded.
+    std::vector<std::vector<CadFeature>> m_undo;
+    std::vector<std::vector<CadFeature>> m_redo;
+    static constexpr size_t k_undo_cap = 200;
+};
+
+} // namespace Slic3r
+
+#endif // slic3r_CadDocument_hpp_
@@ -0,0 +1,442 @@
+#include "GeometryEngine.hpp"
+
+#include <BRepMesh_IncrementalMesh.hxx>
+#include <BRep_Tool.hxx>
+#include <BRepAdaptor_Surface.hxx>
+#include <BRepLProp_SLProps.hxx>
+#include <gp_Cylinder.hxx>
+#include <BRepFilletAPI_MakeFillet.hxx>
+#include <BRepFilletAPI_MakeChamfer.hxx>
+#include <stdexcept>
+#include <TopExp_Explorer.hxx>
+#include <TopoDS.hxx>
+#include <TopoDS_Face.hxx>
+#include <TopoDS_Edge.hxx>
+#include <TopExp.hxx>
+#include <TopTools.hxx>
+#include <TopTools_IndexedMapOfShape.hxx>
+#include <Poly_Triangulation.hxx>
+#include <gp_Ax2.hxx>
+#include <gp_Dir.hxx>
+#include <gp_Pnt.hxx>
+#include <BRepGProp.hxx>
+#include <GProp_GProps.hxx>
+#include <GeomLProp_SLProps.hxx>
+#include <BRepAdaptor_Curve.hxx>
+#include <GCPnts_TangentialDeflection.hxx>
+#include <STEPControl_Reader.hxx>
+#include <IFSelect_ReturnStatus.hxx>
+#include <Standard_Failure.hxx>
+
+namespace Slic3r {
+
+// ---- STEP import (B-rep, not mesh) ----
+std::vector<TopoDS_Shape> GeometryEngine::read_step_solids(const std::string& path, std::string& err)
+{
+    err.clear();
+    std::vector<TopoDS_Shape> out;
+    try {
+        STEPControl_Reader reader;
+        if (reader.ReadFile(path.c_str()) != IFSelect_RetDone) {
+            err = "cannot read STEP file";
+            return out;
+        }
+        reader.TransferRoots();
+        const TopoDS_Shape shape = reader.OneShape();
+        if (shape.IsNull()) { err = "STEP file has no geometry"; return out; }
+        // One body per top-level solid; fall back to the whole shape (shells/faces) if none.
+        for (TopExp_Explorer ex(shape, TopAbs_SOLID); ex.More(); ex.Next())
+            out.push_back(ex.Current());
+        if (out.empty())
+            out.push_back(shape);
+    } catch (const Standard_Failure& e) {
+        err = e.GetMessageString() ? e.GetMessageString() : "OCCT failed to read STEP";
+        out.clear();
+    }
+    return out;
+}
+
+// ---- Primitive creation ----
+
+TopoDS_Solid GeometryEngine::make_primitive(const PrimitiveParams& params)
+{
+    switch (params.type) {
+    case PrimitiveType::Box:
+        return BRepPrimAPI_MakeBox(gp_Pnt(-params.box_w/2, -params.box_d/2, 0),
+                                   params.box_w, params.box_d, params.box_h).Solid();
+    case PrimitiveType::Cylinder:
+        return BRepPrimAPI_MakeCylinder(gp_Ax2(gp_Pnt(0,0,0), gp_Dir(0,0,1)),
+                                        params.cyl_radius, params.cyl_height).Solid();
+    case PrimitiveType::Sphere:
+        return BRepPrimAPI_MakeSphere(gp_Pnt(0,0,params.sph_radius), params.sph_radius).Solid();
+    case PrimitiveType::Cone:
+        return BRepPrimAPI_MakeCone(gp_Ax2(gp_Pnt(0,0,0), gp_Dir(0,0,1)),
+                                    params.cone_r1, params.cone_r2, params.cone_height).Solid();
+    case PrimitiveType::Torus:
+        return BRepPrimAPI_MakeTorus(gp_Ax2(gp_Pnt(0,0,params.torus_r2), gp_Dir(0,0,1)),
+                                     params.torus_r1, params.torus_r2).Solid();
+    default:
+        return BRepPrimAPI_MakeBox(gp_Pnt(-10,-10,0), 20,20,20).Solid();
+    }
+}
+
+// ---- Face classification ----
+
+FaceGroup GeometryEngine::classify_face(const TopoDS_Face& face, const TopoDS_Shape& /*solid*/)
+{
+    try {
+        BRepAdaptor_Surface surf(face);
+        if (surf.GetType() == GeomAbs_Plane) {
+            // Sample normal at center UV
+            double u = (surf.FirstUParameter() + surf.LastUParameter()) / 2.0;
+            double v = (surf.FirstVParameter() + surf.LastVParameter()) / 2.0;
+            gp_Pnt pt; gp_Vec du, dv;
+            surf.D1(u, v, pt, du, dv);
+            gp_Dir n = du.Crossed(dv);
+            if (face.Orientation() == TopAbs_REVERSED) n.Reverse();
+
+            if (n.Z() > 0.7)  return FaceGroup::Top;
+            if (n.Z() < -0.7) return FaceGroup::Bottom;
+            return FaceGroup::Lateral;
+        }
+    } catch (...) {}
+    return FaceGroup::Lateral;
+}
+
+// ---- Edge collection ----
+
+std::vector<TopoDS_Edge> GeometryEngine::collect_edges(const TopoDS_Shape& solid, FaceGroup target)
+{
+    std::vector<TopoDS_Edge> result;
+    if (target == FaceGroup::All) {
+        for (TopExp_Explorer exp(solid, TopAbs_EDGE); exp.More(); exp.Next())
+            result.push_back(TopoDS::Edge(exp.Current()));
+        return result;
+    }
+
+    // Build edge-to-face map once
+    TopTools_IndexedDataMapOfShapeListOfShape edgeFaceMap;
+    TopExp::MapShapesAndAncestors(solid, TopAbs_EDGE, TopAbs_FACE, edgeFaceMap);
+
+    for (TopExp_Explorer edgeExp(solid, TopAbs_EDGE); edgeExp.More(); edgeExp.Next()) {
+        const TopoDS_Edge& edge = TopoDS::Edge(edgeExp.Current());
+        if (!edgeFaceMap.Contains(edge)) continue;
+        const TopTools_ListOfShape& faces = edgeFaceMap.FindFromKey(edge);
+
+        bool include = false;
+        for (auto it = faces.begin(); it != faces.end(); ++it) {
+            FaceGroup fg = classify_face(TopoDS::Face(*it), solid);
+            if (target == FaceGroup::Top && fg == FaceGroup::Top)       { include = true; break; }
+            if (target == FaceGroup::Bottom && fg == FaceGroup::Bottom) { include = true; break; }
+            if (target == FaceGroup::Lateral && fg == FaceGroup::Lateral) { include = true; break; }
+        }
+
+        if (!include && target == FaceGroup::Top) {
+            for (auto it = faces.begin(); it != faces.end(); ++it) {
+                if (classify_face(TopoDS::Face(*it), solid) == FaceGroup::Top) { include = true; break; }
+            }
+        }
+        if (!include && target == FaceGroup::Bottom) {
+            for (auto it = faces.begin(); it != faces.end(); ++it) {
+                if (classify_face(TopoDS::Face(*it), solid) == FaceGroup::Bottom) { include = true; break; }
+            }
+        }
+        if (target == FaceGroup::Lateral && !include) {
+            int lateralCount = 0;
+            for (auto it = faces.begin(); it != faces.end(); ++it) {
+                if (classify_face(TopoDS::Face(*it), solid) == FaceGroup::Lateral) ++lateralCount;
+            }
+            if (lateralCount >= 2) include = true;
+        }
+
+        if (include) result.push_back(edge);
+    }
+
+    return result;
+}
+
+// ---- Fillet/Chamfer ----
+
+TopoDS_Shape GeometryEngine::apply_fillet(const TopoDS_Shape& solid, double radius, FaceGroup faces)
+{
+    if (radius <= 0.001) return solid;
+
+    std::vector<TopoDS_Edge> edges = collect_edges(solid, faces);
+    if (edges.empty()) return solid;
+
+    BRepFilletAPI_MakeFillet fillet(solid);
+    for (const auto& edge : edges)
+        fillet.Add(radius, edge);
+    fillet.Build();
+
+    // A too-large radius (e.g. >= half the smallest spanned dimension) makes the
+    // operation degenerate; OCCT leaves IsDone() false. Report it instead of
+    // silently returning the unfilleted solid (which reads as a false success).
+    if (!fillet.IsDone()) throw std::runtime_error("fillet radius too large for this geometry");
+    return fillet.Shape();
+}
+
+TopoDS_Shape GeometryEngine::apply_chamfer(const TopoDS_Shape& solid, double distance, FaceGroup faces)
+{
+    if (distance <= 0.001) return solid;
+
+    std::vector<TopoDS_Edge> edges = collect_edges(solid, faces);
+    if (edges.empty()) return solid;
+
+    BRepFilletAPI_MakeChamfer chamfer(solid);
+    for (const auto& edge : edges)
+        chamfer.Add(distance, edge); // symmetric chamfer
+    chamfer.Build();
+
+    if (!chamfer.IsDone()) throw std::runtime_error("chamfer distance too large for this geometry");
+    return chamfer.Shape();
+}
+
+TopoDS_Shape GeometryEngine::apply_fillet(const TopoDS_Shape& solid, double radius, int edge_id)
+{
+    if (radius <= 0.001) return solid;
+
+    TopoDS_Edge edge = edge_by_index(solid, edge_id);
+    if (edge.IsNull()) throw std::runtime_error("apply_fillet: invalid edge id");
+
+    BRepFilletAPI_MakeFillet mk(solid);
+    mk.Add(radius, edge);
+    mk.Build();
+
+    if (!mk.IsDone()) throw std::runtime_error("apply_fillet: OCCT fillet failed");
+    return mk.Shape();
+}
+
+TopoDS_Shape GeometryEngine::apply_chamfer(const TopoDS_Shape& solid, double distance, int edge_id)
+{
+    if (distance <= 0.001) return solid;
+
+    TopoDS_Edge edge = edge_by_index(solid, edge_id);
+    if (edge.IsNull()) throw std::runtime_error("apply_chamfer: invalid edge id");
+
+    BRepFilletAPI_MakeChamfer mk(solid);
+    mk.Add(distance, edge);
+    mk.Build();
+
+    if (!mk.IsDone()) throw std::runtime_error("apply_chamfer: OCCT chamfer failed");
+    return mk.Shape();
+}
+
+// ---- Tessellation ----
+
+TriangleMesh GeometryEngine::tessellate(const TopoDS_Shape& shape,
+                                        double linear_deflection,
+                                        double angular_deflection)
+{
+    BRepMesh_IncrementalMesh mesh(shape, linear_deflection, false, angular_deflection, true);
+
+    int nbNodes = 0, nbTri = 0;
+    for (TopExp_Explorer exp(shape, TopAbs_FACE); exp.More(); exp.Next()) {
+        TopLoc_Location loc;
+        Handle(Poly_Triangulation) tri = BRep_Tool::Triangulation(TopoDS::Face(exp.Current()), loc);
+        if (!tri.IsNull()) { nbNodes += tri->NbNodes(); nbTri += tri->NbTriangles(); }
+    }
+    if (nbTri == 0 || nbNodes == 0) return TriangleMesh{};
+
+    stl_file stl;
+    stl.stats.type = inmemory;
+    stl.stats.number_of_facets = (uint32_t)nbTri;
+    stl.stats.original_num_facets = stl.stats.number_of_facets;
+    stl_allocate(&stl);
+
+    std::vector<Vec3f> pts; pts.reserve(nbNodes);
+    int ndOff = 0, trOff = 0;
+    for (TopExp_Explorer exp(shape, TopAbs_FACE); exp.More(); exp.Next()) {
+        const TopoDS_Shape& F = exp.Current();
+        TopLoc_Location loc;
+        Handle(Poly_Triangulation) tri = BRep_Tool::Triangulation(TopoDS::Face(F), loc);
+        if (tri.IsNull()) continue;
+        gp_Trsf T = loc.Transformation();
+        for (int i = 1; i <= tri->NbNodes(); ++i) {
+            gp_Pnt p = tri->Node(i); p.Transform(T);
+            pts.emplace_back(Vec3f(p.X(), p.Y(), p.Z()));
+        }
+        auto orient = exp.Current().Orientation();
+        int ids[3];
+        for (int i = 1; i <= tri->NbTriangles(); ++i) {
+            Poly_Triangle t = tri->Triangle(i); t.Get(ids[0], ids[1], ids[2]);
+            if (orient == TopAbs_REVERSED) std::swap(ids[1], ids[2]);
+            stl_facet f;
+            f.vertex[0] = pts[ids[0]+ndOff-1].cast<float>();
+            f.vertex[1] = pts[ids[1]+ndOff-1].cast<float>();
+            f.vertex[2] = pts[ids[2]+ndOff-1].cast<float>();
+            f.extra[0]=0; f.extra[1]=0;
+            stl_normal n; stl_calculate_normal(n,&f); stl_normalize_vector(n);
+            f.normal=n; stl.facet_start[trOff+i-1]=f;
+        }
+        ndOff += tri->NbNodes(); trOff += tri->NbTriangles();
+    }
+    TriangleMesh result; result.from_stl(stl); return result;
+}
+
+std::string GeometryEngine::primitive_name(PrimitiveType type)
+{
+    switch (type) {
+    case PrimitiveType::Box:      return "Box";
+    case PrimitiveType::Cylinder: return "Cylinder";
+    case PrimitiveType::Sphere:   return "Sphere";
+    case PrimitiveType::Cone:     return "Cone";
+    case PrimitiveType::Torus:    return "Torus";
+    default:                      return "Unknown";
+    }
+}
+
+// ---- Topology accessors ----
+
+int GeometryEngine::face_count(const TopoDS_Shape& shape)
+{
+    int n = 0;
+    for (TopExp_Explorer e(shape, TopAbs_FACE); e.More(); e.Next())
+        ++n;
+    return n;
+}
+
+TopoDS_Face GeometryEngine::face_by_index(const TopoDS_Shape& shape, int index)
+{
+    if (index < 0) return TopoDS_Face();
+    int ordinal = 0;
+    for (TopExp_Explorer e(shape, TopAbs_FACE); e.More(); e.Next()) {
+        if (ordinal == index)
+            return TopoDS::Face(e.Current());
+        ++ordinal;
+    }
+    return TopoDS_Face();
+}
+
+std::vector<TopoDS_Edge> GeometryEngine::edges_of_face(const TopoDS_Face& face)
+{
+    std::vector<TopoDS_Edge> result;
+    TopTools_IndexedMapOfShape map;
+    TopExp::MapShapes(face, TopAbs_EDGE, map);
+    for (int i = 1; i <= map.Extent(); ++i)
+        result.push_back(TopoDS::Edge(map(i)));
+    return result;
+}
+
+std::vector<Vec3d> GeometryEngine::sample_edge_world(const TopoDS_Edge& edge, double chord_tol)
+{
+    if (BRep_Tool::Degenerated(edge))
+        return {};
+
+    BRepAdaptor_Curve curve(edge);
+    GCPnts_TangentialDeflection disc(curve, 0.1, chord_tol);
+
+    std::vector<Vec3d> pts;
+    if (disc.NbPoints() >= 2) {
+        for (int i = 1; i <= disc.NbPoints(); ++i) {
+            gp_Pnt p = disc.Value(i);
+            pts.emplace_back(p.X(), p.Y(), p.Z());
+        }
+    } else {
+        gp_Pnt p0 = curve.Value(curve.FirstParameter());
+        gp_Pnt p1 = curve.Value(curve.LastParameter());
+        pts.emplace_back(p0.X(), p0.Y(), p0.Z());
+        pts.emplace_back(p1.X(), p1.Y(), p1.Z());
+    }
+    return pts;
+}
+
+Vec3d GeometryEngine::face_centroid_world(const TopoDS_Face& face)
+{
+    GProp_GProps props;
+    BRepGProp::SurfaceProperties(face, props);
+    gp_Pnt c = props.CentreOfMass();
+    return Vec3d(c.X(), c.Y(), c.Z());
+}
+
+Vec3d GeometryEngine::face_normal_world(const TopoDS_Face& face)
+{
+    BRepAdaptor_Surface surf(face);
+    const double u = 0.5 * (surf.FirstUParameter() + surf.LastUParameter());
+    const double v = 0.5 * (surf.FirstVParameter() + surf.LastVParameter());
+    BRepLProp_SLProps props(surf, u, v, 1, 1e-6);
+    gp_Dir n(0.0, 0.0, 1.0);
+    if (props.IsNormalDefined()) n = props.Normal();
+    if (face.Orientation() == TopAbs_REVERSED) n.Reverse();   // outward (account for face winding)
+    return Vec3d(n.X(), n.Y(), n.Z());
+}
+
+GeometryEngine::CylinderFace GeometryEngine::cylinder_of_face(const TopoDS_Face& face)
+{
+    CylinderFace cf;
+    if (face.IsNull()) return cf;
+    BRepAdaptor_Surface surf(face);
+    if (surf.GetType() != GeomAbs_Cylinder) return cf;
+
+    const gp_Cylinder cyl = surf.Cylinder();
+    const gp_Ax1      ax  = cyl.Axis();
+    const Vec3d axis(ax.Direction().X(), ax.Direction().Y(), ax.Direction().Z());
+    const Vec3d apt (ax.Location().X(),  ax.Location().Y(),  ax.Location().Z());
+    cf.radius = cyl.Radius();
+
+    // Axial extent: V is the axial parameter on a cylinder; bound the face's two ends and
+    // order them so `axis` points base -> top.
+    const double umid = 0.5 * (surf.FirstUParameter() + surf.LastUParameter());
+    const gp_Pnt e0 = surf.Value(umid, surf.FirstVParameter());
+    const gp_Pnt e1 = surf.Value(umid, surf.LastVParameter());
+    double t0 = (Vec3d(e0.X(), e0.Y(), e0.Z()) - apt).dot(axis);
+    double t1 = (Vec3d(e1.X(), e1.Y(), e1.Z()) - apt).dot(axis);
+    if (t1 < t0) std::swap(t0, t1);
+    cf.base   = apt + axis * t0;
+    cf.axis   = axis;
+    cf.height = t1 - t0;
+
+    // Internal (bore) vs external: compare the face's outward normal at its centre to the
+    // outward radial direction. A bore's normal points toward the axis (dot < 0).
+    const gp_Pnt sp = surf.Value(umid, 0.5 * (surf.FirstVParameter() + surf.LastVParameter()));
+    const Vec3d  S(sp.X(), sp.Y(), sp.Z());
+    const Vec3d  axpt   = cf.base + axis * (S - cf.base).dot(axis);
+    const Vec3d  radial = (S - axpt).normalized();
+    cf.internal = face_normal_world(face).dot(radial) < 0.0;
+    cf.ok = true;
+    return cf;
+}
+
+bool GeometryEngine::face_plane_bounds(const TopoDS_Face& face, const Vec3d& origin,
+                                       const Vec3d& x_axis, const Vec3d& y_axis,
+                                       double& umin, double& umax, double& vmin, double& vmax)
+{
+    umin = vmin = 1e30; umax = vmax = -1e30;
+    bool any = false;
+    for (TopExp_Explorer ex(face, TopAbs_VERTEX); ex.More(); ex.Next()) {
+        const gp_Pnt p = BRep_Tool::Pnt(TopoDS::Vertex(ex.Current()));
+        const Vec3d P(p.X(), p.Y(), p.Z());
+        const double u = (P - origin).dot(x_axis);
+        const double v = (P - origin).dot(y_axis);
+        umin = std::min(umin, u); umax = std::max(umax, u);
+        vmin = std::min(vmin, v); vmax = std::max(vmax, v);
+        any = true;
+    }
+    return any;
+}
+
+int GeometryEngine::edge_count(const TopoDS_Shape& shape)
+{
+    TopTools_IndexedMapOfShape map;
+    TopExp::MapShapes(shape, TopAbs_EDGE, map);
+    return map.Extent();
+}
+
+TopoDS_Edge GeometryEngine::edge_by_index(const TopoDS_Shape& shape, int index)
+{
+    TopTools_IndexedMapOfShape map;
+    TopExp::MapShapes(shape, TopAbs_EDGE, map);
+    if (index < 0 || index >= map.Extent())
+        return TopoDS_Edge();
+    return TopoDS::Edge(map(index + 1));
+}
+
+int GeometryEngine::edge_index_of(const TopoDS_Shape& shape, const TopoDS_Edge& edge)
+{
+    TopTools_IndexedMapOfShape map;
+    TopExp::MapShapes(shape, TopAbs_EDGE, map);
+    int idx = map.FindIndex(edge);
+    return (idx > 0) ? (idx - 1) : -1;
+}
+
+} // namespace Slic3r
@@ -0,0 +1,121 @@
+#ifndef slic3r_GeometryEngine_hpp_
+#define slic3r_GeometryEngine_hpp_
+
+#include "TriangleMesh.hpp"
+
+#include <BRepPrimAPI_MakeBox.hxx>
+#include <BRepPrimAPI_MakeCylinder.hxx>
+#include <BRepPrimAPI_MakeSphere.hxx>
+#include <BRepPrimAPI_MakeCone.hxx>
+#include <BRepPrimAPI_MakeTorus.hxx>
+#include <gp_Ax2.hxx>
+#include <TopoDS_Solid.hxx>
+#include <TopoDS_Face.hxx>
+#include <TopoDS_Edge.hxx>
+#include <vector>
+#include <string>
+
+namespace Slic3r {
+
+enum class PrimitiveType { Box, Cylinder, Sphere, Cone, Torus, COUNT };
+enum class DressUpType   { Fillet, Chamfer };
+enum class FaceGroup     { Top, Bottom, Lateral, All };
+
+struct PrimitiveParams {
+    PrimitiveType type{PrimitiveType::Box};
+    double box_w{20}, box_h{20}, box_d{20};
+    double cyl_radius{10}, cyl_height{20};
+    double sph_radius{10};
+    double cone_r1{10}, cone_r2{5}, cone_height{20};
+    double torus_r1{10}, torus_r2{3};
+
+    // Dress-up
+    bool   dressup_enabled{false};
+    DressUpType dressup_type{DressUpType::Fillet};
+    FaceGroup   dressup_faces{FaceGroup::All};
+    double dressup_radius{1.0};    // fillet radius
+    double dressup_chamfer_dist{1.0}; // chamfer distance (symmetric)
+
+    // Mesh quality
+    double linear_deflection{0.01};
+    double angular_deflection{0.5};
+
+    template<class Archive>
+    void serialize(Archive& ar) {
+        ar(type, box_w, box_h, box_d, cyl_radius, cyl_height, sph_radius,
+           cone_r1, cone_r2, cone_height, torus_r1, torus_r2,
+           dressup_enabled, dressup_type, dressup_faces, dressup_radius, dressup_chamfer_dist,
+           linear_deflection, angular_deflection);
+    }
+};
+
+class GeometryEngine
+{
+public:
+    static TopoDS_Solid make_primitive(const PrimitiveParams& params);
+
+    // Read a STEP file into its top-level solids (one TopoDS_Shape per solid; falls back to
+    // the whole shape if it contains no closed solids). Reuses OCCT's STEPControl_Reader,
+    // already linked via Format/STEP.cpp — no new dependency. err is set on failure (empty result).
+    static std::vector<TopoDS_Shape> read_step_solids(const std::string& path, std::string& err);
+
+    static TopoDS_Shape apply_fillet(const TopoDS_Shape& solid, double radius,
+                                     FaceGroup faces = FaceGroup::All);
+    static TopoDS_Shape apply_fillet(const TopoDS_Shape& solid, double radius,
+                                     int edge_id);
+    static TopoDS_Shape apply_chamfer(const TopoDS_Shape& solid, double distance,
+                                       FaceGroup faces = FaceGroup::All);
+    static TopoDS_Shape apply_chamfer(const TopoDS_Shape& solid, double distance,
+                                       int edge_id);
+
+    static TriangleMesh tessellate(const TopoDS_Shape& shape,
+                                   double linear_deflection = 0.01,
+                                   double angular_deflection = 0.5);
+    static std::string  primitive_name(PrimitiveType type);
+
+    // Topology accessors for in-viewport face/edge picking (Design tab). Face index is the
+    // TopExp_Explorer(shape, TopAbs_FACE) ordinal — identical to SketchEngine::tessellate's
+    // per-triangle face id, so a picked triangle's id maps back to a face here.
+    static TopoDS_Face face_by_index(const TopoDS_Shape& shape, int index);  // null if out of range
+    static int         face_count(const TopoDS_Shape& shape);
+    static std::vector<TopoDS_Edge> edges_of_face(const TopoDS_Face& face);
+    // Centre of mass (world) of a face — used to compute the extrude length for "up to face".
+    static Vec3d face_centroid_world(const TopoDS_Face& face);
+    // Outward unit normal of a face at its UV midpoint (orientation-aware) — for the shell gizmo.
+    static Vec3d face_normal_world(const TopoDS_Face& face);
+    // Sample an edge into a world-space polyline (>=2 pts) for pick-distance + highlight.
+    static std::vector<Vec3d> sample_edge_world(const TopoDS_Edge& edge, double chord_tol = 0.05);
+    // 0-based edge index into TopExp::MapShapes(shape, TopAbs_EDGE, map).
+    static int          edge_count(const TopoDS_Shape& shape);
+    static TopoDS_Edge  edge_by_index(const TopoDS_Shape& shape, int index);
+    static int          edge_index_of(const TopoDS_Shape& shape, const TopoDS_Edge& edge);
+
+    // Analysis of a cylindrical face for the Thread tool (a hole bore or a cylinder's lateral
+    // surface): axis (base at the lower axial end + unit direction), radius, axial extent, and
+    // whether it is a bore (face normal points toward the axis = internal thread). ok=false if
+    // the face is not a cylinder.
+    struct CylinderFace {
+        bool   ok{false};
+        Vec3d  base{0, 0, 0};
+        Vec3d  axis{0, 0, 1};
+        double radius{0};
+        double height{0};
+        bool   internal{false};
+    };
+    static CylinderFace cylinder_of_face(const TopoDS_Face& face);
+
+    // Plane-coordinate (u,v) bounding box of a face's vertices, measured from `origin` along
+    // `x_axis`/`y_axis`. Lets the Hole tool dimension the hole from the face SIDES (umin/vmin =
+    // two adjacent edges) instead of from the centre. Returns false if the face has no vertices.
+    static bool face_plane_bounds(const TopoDS_Face& face, const Vec3d& origin,
+                                  const Vec3d& x_axis, const Vec3d& y_axis,
+                                  double& umin, double& umax, double& vmin, double& vmax);
+
+private:
+    static std::vector<TopoDS_Edge> collect_edges(const TopoDS_Shape& solid, FaceGroup faces);
+    static FaceGroup classify_face(const TopoDS_Face& face, const TopoDS_Shape& solid);
+};
+
+} // namespace Slic3r
+
+#endif // slic3r_GeometryEngine_hpp_
@@ -0,0 +1,307 @@
+#include "SketchConstraints.hpp"
+#include <Eigen/Dense>
+#include <cmath>
+
+namespace Slic3r {
+
+int SketchConstraints::add_point(double x, double y)
+{
+    m_vars.push_back(x);
+    m_vars.push_back(y);
+    return static_cast<int>(m_vars.size() / 2) - 1;
+}
+
+void SketchConstraints::set_point(int id, double x, double y)
+{
+    size_t idx = 2 * id;
+    m_vars[idx]     = x;
+    m_vars[idx + 1] = y;
+}
+
+Vec2d SketchConstraints::get_point(int id) const
+{
+    size_t idx = 2 * id;
+    return Vec2d(m_vars[idx], m_vars[idx + 1]);
+}
+
+int SketchConstraints::point_count() const
+{
+    return static_cast<int>(m_vars.size() / 2);
+}
+
+void SketchConstraints::fix_point(int id)
+{
+    size_t idx = 2 * id;
+    Con c;
+    c.type = FIX_POINT;
+    c.a    = id;
+    c.b = c.c = c.d = 0;
+    c.k0   = m_vars[idx];
+    c.k1   = m_vars[idx + 1];
+    m_cons.push_back(c);
+}
+
+void SketchConstraints::coincident(int a, int b)
+{
+    Con c;
+    c.type = COINCIDENT;
+    c.a = a; c.b = b; c.c = c.d = 0;
+    c.k0 = c.k1 = 0;
+    m_cons.push_back(c);
+}
+
+void SketchConstraints::horizontal(int a, int b)
+{
+    Con c;
+    c.type = HORIZONTAL;
+    c.a = a; c.b = b; c.c = c.d = 0;
+    c.k0 = c.k1 = 0;
+    m_cons.push_back(c);
+}
+
+void SketchConstraints::vertical(int a, int b)
+{
+    Con c;
+    c.type = VERTICAL;
+    c.a = a; c.b = b; c.c = c.d = 0;
+    c.k0 = c.k1 = 0;
+    m_cons.push_back(c);
+}
+
+void SketchConstraints::distance(int a, int b, double d)
+{
+    Con c;
+    c.type = DISTANCE;
+    c.a = a; c.b = b; c.c = c.d = 0;
+    c.k0 = d; c.k1 = 0;
+    m_cons.push_back(c);
+}
+
+void SketchConstraints::lock_x(int id, double x)
+{
+    Con c;
+    c.type = LOCK_X;
+    c.a = id;
+    c.b = c.c = c.d = 0;
+    c.k0 = x; c.k1 = 0;
+    m_cons.push_back(c);
+}
+
+void SketchConstraints::lock_y(int id, double y)
+{
+    Con c;
+    c.type = LOCK_Y;
+    c.a = id;
+    c.b = c.c = c.d = 0;
+    c.k0 = y; c.k1 = 0;
+    m_cons.push_back(c);
+}
+
+void SketchConstraints::equal_length(int a, int b, int c, int d)
+{
+    Con con;
+    con.type = EQUAL_LENGTH;
+    con.a = a; con.b = b; con.c = c; con.d = d;
+    con.k0 = con.k1 = 0;
+    m_cons.push_back(con);
+}
+
+void SketchConstraints::parallel(int a, int b, int c, int d)
+{
+    Con con;
+    con.type = PARALLEL;
+    con.a = a; con.b = b; con.c = c; con.d = d;
+    con.k0 = con.k1 = 0;
+    m_cons.push_back(con);
+}
+
+void SketchConstraints::perpendicular(int a, int b, int c, int d)
+{
+    Con con;
+    con.type = PERPENDICULAR;
+    con.a = a; con.b = b; con.c = c; con.d = d;
+    con.k0 = con.k1 = 0;
+    m_cons.push_back(con);
+}
+
+void SketchConstraints::midpoint(int m, int a, int b)
+{
+    Con con;
+    con.type = MIDPOINT;
+    con.a = m; con.b = a; con.c = b; con.d = -1;
+    con.k0 = con.k1 = 0;
+    m_cons.push_back(con);
+}
+
+void SketchConstraints::symmetric(int a, int b, int c, int d)
+{
+    Con con;
+    con.type = SYMMETRIC;
+    con.a = a; con.b = b; con.c = c; con.d = d;
+    con.k0 = con.k1 = 0;
+    m_cons.push_back(con);
+}
+
+void SketchConstraints::angle(int a, int b, int c, int d, double radians)
+{
+    Con con;
+    con.type = ANGLE;
+    con.a = a; con.b = b; con.c = c; con.d = d;
+    con.k0 = radians; con.k1 = 0;
+    m_cons.push_back(con);
+}
+
+void SketchConstraints::point_line_distance(int p, int a, int b, double dist)
+{
+    Con con;
+    con.type = PT_LINE_DIST;
+    con.a = p; con.b = a; con.c = b; con.d = -1;
+    con.k0 = dist; con.k1 = 0;
+    m_cons.push_back(con);
+}
+
+Eigen::VectorXd SketchConstraints::residuals(const std::vector<double>& v) const
+{
+    auto X = [&](int i) { return v[2 * i]; };
+    auto Y = [&](int i) { return v[2 * i + 1]; };
+
+    std::vector<double> res;
+    for (const auto& c : m_cons) {
+        switch (c.type) {
+        case FIX_POINT:
+            res.push_back(X(c.a) - c.k0);
+            res.push_back(Y(c.a) - c.k1);
+            break;
+        case COINCIDENT:
+            res.push_back(X(c.a) - X(c.b));
+            res.push_back(Y(c.a) - Y(c.b));
+            break;
+        case HORIZONTAL:
+            res.push_back(Y(c.a) - Y(c.b));
+            break;
+        case VERTICAL:
+            res.push_back(X(c.a) - X(c.b));
+            break;
+        case DISTANCE:
+            res.push_back(std::hypot(X(c.a) - X(c.b), Y(c.a) - Y(c.b)) - c.k0);
+            break;
+        case LOCK_X:
+            res.push_back(X(c.a) - c.k0);
+            break;
+        case LOCK_Y:
+            res.push_back(Y(c.a) - c.k0);
+            break;
+        case EQUAL_LENGTH:
+            res.push_back(std::hypot(X(c.a) - X(c.b), Y(c.a) - Y(c.b)) -
+                          std::hypot(X(c.c) - X(c.d), Y(c.c) - Y(c.d)));
+            break;
+        case PARALLEL:
+            res.push_back((X(c.b) - X(c.a)) * (Y(c.d) - Y(c.c)) -
+                          (Y(c.b) - Y(c.a)) * (X(c.d) - X(c.c)));
+            break;
+        case PERPENDICULAR:
+            res.push_back((X(c.b) - X(c.a)) * (X(c.d) - X(c.c)) +
+                          (Y(c.b) - Y(c.a)) * (Y(c.d) - Y(c.c)));
+            break;
+        case MIDPOINT:
+            res.push_back(X(c.a) - 0.5 * (X(c.b) + X(c.c)));
+            res.push_back(Y(c.a) - 0.5 * (Y(c.b) + Y(c.c)));
+            break;
+        case SYMMETRIC: {
+            const double abx = X(c.b) - X(c.a), aby = Y(c.b) - Y(c.a);
+            const double cdx = X(c.d) - X(c.c), cdy = Y(c.d) - Y(c.c);
+            res.push_back(abx * cdx + aby * cdy);
+            const double mx = 0.5 * (X(c.a) + X(c.b));
+            const double my = 0.5 * (Y(c.a) + Y(c.b));
+            res.push_back((mx - X(c.c)) * cdy - (my - Y(c.c)) * cdx);
+            break;
+        }
+        case ANGLE: {
+            const double ux = X(c.b) - X(c.a), uy = Y(c.b) - Y(c.a);
+            const double wx = X(c.d) - X(c.c), wy = Y(c.d) - Y(c.c);
+            const double cross = ux * wy - uy * wx;
+            const double dot   = ux * wx + uy * wy;
+            res.push_back(std::atan2(cross, dot) - c.k0);
+            break;
+        }
+        case PT_LINE_DIST: {
+            const double bx = X(c.b), by = Y(c.b);
+            const double cx = X(c.c), cy = Y(c.c);
+            const double L  = std::hypot(cx - bx, cy - by);
+            const double num = (X(c.a) - bx) * (cy - by) - (Y(c.a) - by) * (cx - bx);
+            res.push_back((L > 1e-12 ? std::abs(num) / L : 0.0) - c.k0);
+            break;
+        }
+        }
+    }
+
+    Eigen::VectorXd r(static_cast<Eigen::Index>(res.size()));
+    for (size_t i = 0; i < res.size(); ++i)
+        r(static_cast<Eigen::Index>(i)) = res[i];
+    return r;
+}
+
+Eigen::MatrixXd SketchConstraints::jacobian(const std::vector<double>& v) const
+{
+    int m = static_cast<int>(residuals(v).size());
+    int n = static_cast<int>(v.size());
+    Eigen::MatrixXd J(m, n);
+    const double eps = 1e-7;
+
+    std::vector<double> vp = v;
+    std::vector<double> vm = v;
+
+    for (int j = 0; j < n; ++j) {
+        vp[j] = v[j] + eps;
+        vm[j] = v[j] - eps;
+        Eigen::VectorXd rp = residuals(vp);
+        Eigen::VectorXd rm = residuals(vm);
+        vp[j] = v[j];
+        vm[j] = v[j];
+        J.col(j) = (rp - rm) / (2.0 * eps);
+    }
+
+    return J;
+}
+
+bool SketchConstraints::solve(int max_iter, double tol)
+{
+    if (m_cons.empty()) return true;
+    double lambda = 1e-3;
+    Eigen::VectorXd r = residuals(m_vars);
+    for (int it = 0; it < max_iter; ++it) {
+        double rn = r.norm();
+        if (rn < tol) return true;
+        Eigen::MatrixXd J = jacobian(m_vars);
+        Eigen::MatrixXd A = J.transpose() * J;
+        Eigen::VectorXd g = J.transpose() * r;
+        bool stepped = false;
+        for (int t = 0; t < 12; ++t) {
+            Eigen::MatrixXd Ad = A;
+            for (int i = 0; i < Ad.rows(); ++i)
+                Ad(i, i) += lambda * (1.0 + Ad(i, i));
+            Eigen::VectorXd dx = Ad.ldlt().solve(-g);
+            std::vector<double> cand = m_vars;
+            for (size_t i = 0; i < cand.size(); ++i)
+                cand[i] += dx[static_cast<Eigen::Index>(i)];
+            Eigen::VectorXd rc = residuals(cand);
+            if (rc.norm() < rn) {
+                m_vars = cand;
+                r      = rc;
+                lambda = std::max(lambda * 0.4, 1e-12);
+                stepped = true;
+                break;
+            }
+            lambda *= 3.0;
+        }
+        if (!stepped) break;
+    }
+    return r.norm() < tol * 100;
+}
+
+double SketchConstraints::residual_norm() const
+{
+    return residuals(m_vars).norm();
+}
+
+} // namespace Slic3r
@@ -0,0 +1,68 @@
+#ifndef slic3r_SketchConstraints_hpp_
+#define slic3r_SketchConstraints_hpp_
+
+#include "libslic3r/Point.hpp"
+#include <vector>
+#include <Eigen/Dense>
+
+namespace Slic3r {
+
+class SketchConstraints {
+public:
+    int   add_point(double x, double y);
+    void  set_point(int id, double x, double y);
+    Vec2d get_point(int id) const;
+    int   point_count() const;
+
+    void fix_point(int id);
+    void coincident(int a, int b);
+    void horizontal(int a, int b);
+    void vertical(int a, int b);
+    void distance(int a, int b, double d);
+    void lock_x(int id, double x);
+    void lock_y(int id, double y);
+    void equal_length(int a, int b, int c, int d);
+    void parallel(int a, int b, int c, int d);
+    void perpendicular(int a, int b, int c, int d);
+    void midpoint(int m, int a, int b);
+    void symmetric(int a, int b, int c, int d);
+    void angle(int a, int b, int c, int d, double radians);
+    void point_line_distance(int p, int a, int b, double dist);
+
+    bool   solve(int max_iter = 200, double tol = 1e-10);
+    double residual_norm() const;
+
+private:
+    std::vector<double> m_vars;
+
+    enum ConType : int {
+        FIX_POINT = 0,
+        COINCIDENT,
+        HORIZONTAL,
+        VERTICAL,
+        DISTANCE,
+        LOCK_X,
+        LOCK_Y,
+        EQUAL_LENGTH,
+        PARALLEL,
+        PERPENDICULAR,
+        MIDPOINT,
+        SYMMETRIC,
+        ANGLE,
+        PT_LINE_DIST
+    };
+
+    struct Con {
+        int    type;
+        int    a, b, c, d;
+        double k0, k1;
+    };
+    std::vector<Con> m_cons;
+
+    Eigen::VectorXd residuals(const std::vector<double>& v) const;
+    Eigen::MatrixXd jacobian(const std::vector<double>& v) const;
+};
+
+} // namespace Slic3r
+
+#endif // slic3r_SketchConstraints_hpp_
@@ -0,0 +1,257 @@
+#ifndef slic3r_SketchEngine_hpp_
+#define slic3r_SketchEngine_hpp_
+
+#include "TriangleMesh.hpp"
+#include "libslic3r/Point.hpp"
+#include "GeometryEngine.hpp"
+
+#include <gp_Pln.hxx>
+#include <gp_Ax3.hxx>
+#include <TopoDS_Wire.hxx>
+#include <TopoDS_Shape.hxx>
+#include <TopoDS_Face.hxx>
+#include <vector>
+
+namespace Slic3r {
+
+struct SketchSegment {
+    enum Type { Line, Arc, Circle, Rectangle, Polygon };
+    Type type{Line};
+    Vec2d p0{0,0}, p1{0,0};
+    Vec2d center{0,0};
+    double radius{0}, start_angle{0}, end_angle{0};
+    std::vector<Vec2d> points;
+    template<class Archive>
+    void serialize(Archive& ar) { ar(type, p0, p1, center, radius, start_angle, end_angle, points); }
+};
+
+struct SketchEntity {
+    enum class Type { Line, Arc, Circle, Point, Ellipse, EllipseArc, BSpline };
+    Type   type{Type::Line};
+    Vec2d  p0{0,0};            // Line: start; Arc/EllipseArc: start; Circle/Point/Ellipse: center; BSpline: first pole
+    Vec2d  p1{0,0};            // Line: end;   Arc/EllipseArc: end;   (unused for Circle/Point/Ellipse); BSpline: last pole
+    Vec2d  center{0,0};        // Arc/Circle/Ellipse(Arc) center
+    double radius{0};          // Circle/Arc radius; Ellipse(Arc): semi-major axis (a)
+    double start_angle{0};     // Arc sweep start; Ellipse(Arc): parametric start angle (radians)
+    double end_angle{0};       // Arc sweep end;   Ellipse(Arc): parametric end angle
+    bool   construction{false};
+    double rminor{0};          // Ellipse(Arc): semi-minor axis (b)
+    double rotation{0};        // Ellipse(Arc): major-axis angle phi (radians, about center)
+    std::vector<Vec2d> ctrl;   // BSpline: control points (poles); p0/p1 mirror first/last pole
+    template<class Archive>
+    void serialize(Archive& ar) {
+        // Append-only: rminor/rotation added for Ellipse(Arc) (P2 Tier-B.1); ctrl for BSpline (B.2).
+        ar(type, p0, p1, center, radius, start_angle, end_angle, construction, rminor, rotation, ctrl);
+    }
+};
+
+struct SketchPlane {
+    Vec3d origin{0,0,0};
+    Vec3d normal{0,0,1};
+    Vec3d x_axis{1,0,0};
+    Vec3d y_axis{0,1,0};
+
+    gp_Pln to_occt() const;
+    static SketchPlane from_face(const TopoDS_Face& face);
+    static SketchPlane XY() { return {}; }
+    static SketchPlane XZ() { return {{0,0,0}, {0,1,0}, {1,0,0}, {0,0,1}}; }
+    static SketchPlane YZ() { return {{0,0,0}, {1,0,0}, {0,1,0}, {0,0,1}}; }
+
+    Vec2d project(const Vec3d& ray_origin, const Vec3d& ray_dir) const;
+    Vec3d to_world(const Vec2d& pt) const;
+
+    template<class Archive>
+    void serialize(Archive& ar) { ar(origin, normal, x_axis, y_axis); }
+};
+
+struct SketchProfile {
+    std::vector<Vec2d> points;
+    bool closed{false};
+
+    bool is_closed(double tolerance = 0.5) const;
+    bool try_close(double tolerance = 0.5);
+    void clear() { points.clear(); closed = false; }
+    TopoDS_Wire to_occt_wire(const SketchPlane& plane) const;
+
+    template<class Archive>
+    void serialize(Archive& ar) { ar(points, closed); }
+};
+
+enum class SketchConstraintType {
+    Fix, Coincident, Horizontal, Vertical, Distance,
+    LockX, LockY, EqualLength, Parallel, Perpendicular,
+    Concentric,
+    Tangent, Midpoint, Symmetric, Angle,
+    Radius, Diameter,
+    PointOnLine,  // a point lies on a line (or at signed perpendicular distance `value`)
+    PointOnObject // a point lies on an entity edge (line -> PT_ON_LINE, circle -> PT_ON_CIRCLE)
+};
+
+// Constraint on a SketchProfile, referencing profile point indices (a,b,c,d).
+// `value` carries the target for Distance/LockX/LockY (ignored otherwise).
+struct SketchConstraintDef {
+    SketchConstraintType type{SketchConstraintType::Coincident};
+    int    a{-1}, b{-1}, c{-1}, d{-1};
+    double value{0.0};
+    template<class Archive> void serialize(Archive& ar) { ar(type, a, b, c, d, value); }
+};
+
+// Which point of an entity a constraint reference names.
+//   P0 = SketchEntity::p0 (Line start / Point position)
+//   P1 = SketchEntity::p1 (Line end)
+//   Center = SketchEntity::center (Arc/Circle center)
+enum class SketchPointRole { P0, P1, Center };
+
+// Constraint on coexisting SketchEntity objects (Fase 4.2). Each reference is an
+// (entity index, point role) pair. Point-form constraints
+// (Fix/Coincident/Horizontal/Vertical/Distance/LockX/LockY) use refs A and B as
+// individual points. Segment-form constraints (Parallel/Perpendicular/EqualLength)
+// use entity indices `ea`/`eb` as whole line segments (their P0->P1); roles are
+// ignored for those. `value` carries the target for Distance/LockX/LockY.
+struct SketchEntityConstraintDef {
+    SketchConstraintType type{SketchConstraintType::Coincident};
+    int             ea{-1}, eb{-1};                     // entity indices
+    SketchPointRole ra{SketchPointRole::P0};            // role within ea
+    SketchPointRole rb{SketchPointRole::P0};            // role within eb
+    double          value{0.0};
+    int             ec{-1};                             // third entity ref (Symmetric axis)
+    SketchPointRole rc{SketchPointRole::P0};            // role within ec
+    template<class Archive> void serialize(Archive& ar) { ar(type, ea, eb, ra, rb, value, ec, rc); }
+};
+
+// Solve a bare entity list in place against entity-form constraints. Shared by
+// CadDocument::solve_sketch_feature (committed features) and the in-session GUI
+// sketch tool (live solving as dimensions/constraints are added). Returns true on
+// convergence; an empty constraint list is a no-op that returns true.
+bool solve_sketch_entities(std::vector<SketchEntity>& entities,
+                           const std::vector<SketchEntityConstraintDef>& constraints);
+
+struct SketchParams {
+    // Extrude/Revolve
+    double extrude_len{10}; bool extrude_sym{false}; double extrude_taper{0};
+    double revolve_deg{360};
+    bool   is_pocket{false}; // cut into selected object instead of new
+
+    // Dress-up
+    bool        dressup_enabled{false};
+    DressUpType dressup_type{DressUpType::Fillet};
+    FaceGroup   dressup_faces{FaceGroup::All};
+    double      dressup_radius{1.0};
+    double      dressup_chamfer_dist{1.0};
+
+    // Mesh
+    double linear_deflection{0.01};
+
+    template<class Archive>
+    void serialize(Archive& ar) {
+        ar(extrude_len, extrude_sym, extrude_taper, revolve_deg, is_pocket,
+           dressup_enabled, dressup_type, dressup_faces, dressup_radius, dressup_chamfer_dist,
+           linear_deflection);
+    }
+};
+
+class SketchEngine
+{
+public:
+    static TopoDS_Shape make_extrude(const TopoDS_Wire& wire, const SketchPlane& plane,
+                                     double length, bool symmetric = false, double taper_deg = 0.0);
+    // Asymmetric two-sided prism: extrude the wire's face by `up` along +normal and `down`
+    // along -normal, fused into one solid. up/down are non-negative magnitudes.
+    // Tapered (draft) extrude of a planar wire: the top profile is the base wire offset in its
+    // plane by length*tan(taper_deg), lofted from base to top. Falls back to a straight prism on
+    // any failure (self-intersecting offset / loft error). taper_deg>0 widens the top.
+    static TopoDS_Shape make_extrude_taper(const TopoDS_Wire& wire, const SketchPlane& plane,
+                                           double length, double taper_deg);
+    static TopoDS_Shape make_extrude_two_sided(const TopoDS_Wire& wire, const SketchPlane& plane,
+                                               double up, double down);
+    static TopoDS_Shape make_extrude_face(const TopoDS_Face& face, const SketchPlane& plane,
+                                          double length, bool symmetric = false, double taper_deg = 0.0);
+
+    // Extrude a set of imported rigid regions (Text/SVG). Each region is
+    // contour[0]=outer loop + contour[1..]=hole loops, in plane (u,v) mm. Builds
+    // one planar face-with-holes per region, extrudes it, and fuses all region
+    // solids into a single shape. Empty/degenerate contours are skipped.
+    static TopoDS_Shape make_extrude_regions(
+        const std::vector<std::vector<std::vector<Vec2d>>>& regions,
+        const SketchPlane& plane, double length, bool symmetric = false);
+
+    // Revolve a planar profile wire about an axis lying in the sketch plane and
+    // passing through the plane origin: axis_sel 0 = plane X axis, 1 = plane Y axis.
+    // A negative angle_deg sweeps the opposite direction (Flip). The profile must
+    // lie to one side of the axis (Onshape rule); a straddling profile self-intersects.
+    static TopoDS_Shape make_revolve(const TopoDS_Wire& wire, const SketchPlane& plane,
+                                     double angle_deg = 360.0, int axis_sel = 0);
+
+    // Sweep a planar profile wire along a path (spine) wire. The profile is turned
+    // into a face and swept with BRepOffsetAPI_MakePipe, which keeps the profile
+    // perpendicular to the spine along its length. The path may be open or closed;
+    // for a clean solid the path's first point should sit on/near the profile plane.
+    static TopoDS_Shape make_sweep(const TopoDS_Wire& profile, const TopoDS_Wire& path);
+
+    // Loft a solid through 2+ closed profile wires (each on its own plane), in the
+    // given order. ruled=true => straight (ruled) sections; false => smooth (C2).
+    static TopoDS_Shape make_loft(const std::vector<TopoDS_Wire>& profiles, bool ruled);
+
+    static TopoDS_Shape make_pocket(const TopoDS_Wire& wire, const SketchPlane& plane,
+                                    const TopoDS_Shape& target, double depth);
+
+    static TriangleMesh tessellate(const TopoDS_Shape& shape,
+                                   double linear_deflection = 0.01,
+                                   double angular_deflection = 0.5);
+
+    static TriangleMesh tessellate(const TopoDS_Shape& shape,
+                                   std::vector<int>& tri_face,
+                                   double linear_deflection = 0.01,
+                                   double angular_deflection = 0.5);
+
+    static TopoDS_Wire entities_to_wire(const std::vector<SketchEntity>& entities,
+                                        const SketchPlane& plane);
+
+    static std::vector<SketchEntity> mirror_entities(
+        const std::vector<SketchEntity>& src, const Vec2d& a, const Vec2d& b);
+
+    static std::vector<SketchEntity> offset_entities(
+        const std::vector<SketchEntity>& src, double d);
+
+    // Rigid-transform array. Returns the (count-1) copies for instance i=1..count-1
+    // (the originals in `src` are NOT included). Each copy i is `src` rigidly
+    // transformed by: rotate by i*angle_step about `pivot`, then translate by i*step.
+    //   Rectangular/linear array: angle_step = 0, step = spacing*direction (pivot unused).
+    //   Polar array:              step = (0,0), angle_step = sweep/count, pivot = centre.
+    // Orientation-preserving, so arc/ellipse parametric angles shift by i*angle_step.
+    static std::vector<SketchEntity> array_entities(
+        const std::vector<SketchEntity>& src, int count,
+        const Vec2d& step, double angle_step, const Vec2d& pivot);
+
+    // General affine transform (move / rotate / scale), applied IN PLACE: returns
+    // the SAME entities (same count and order), each mapped by
+    //   p -> pivot + scale * R(angle) * (p - pivot) + move
+    // (radii scale by |scale|; arc/ellipse parametric/rotation angles shift by
+    // `angle`). Unlike array_entities this mutates the subjects rather than adding
+    // copies. Move: angle=0, scale=1. Rotate-in-place: move=(0,0), scale=1,
+    // pivot=centroid. Scale: angle=0.
+    static std::vector<SketchEntity> transform_entities(
+        const std::vector<SketchEntity>& src,
+        const Vec2d& move, double angle, double scale, const Vec2d& pivot);
+
+    static bool fillet_lines(const SketchEntity& a, const SketchEntity& b, double r,
+                             SketchEntity& a_out, SketchEntity& b_out, SketchEntity& arc_out);
+
+    // Symmetric chamfer between two lines meeting at a corner: trims each line back
+    // by setback distance `d` from the shared corner and returns the connecting
+    // straight segment (seg_out) in place of the corner. a_out/b_out are the trimmed
+    // lines; seg_out goes seg_out.p0 (on a) -> seg_out.p1 (on b). False if the lines
+    // are parallel or `d` overruns either line.
+    static bool chamfer_lines(const SketchEntity& a, const SketchEntity& b, double d,
+                              SketchEntity& a_out, SketchEntity& b_out, SketchEntity& seg_out);
+
+    static bool trim_entity(SketchEntity& e, const std::vector<SketchEntity>& others,
+                            const Vec2d& pick);
+
+    static bool extend_entity(SketchEntity& e, const std::vector<SketchEntity>& others,
+                              const Vec2d& pick);
+};
+
+} // namespace Slic3r
+
+#endif // slic3r_SketchEngine_hpp_
@@ -0,0 +1,145 @@
+#include "SketchImport.hpp"
+
+#include "Emboss.hpp"
+#include "NSVGUtils.hpp"
+#include "ExPolygon.hpp"
+#include "TextConfiguration.hpp"   // FontProp
+#include "libslic3r.h"             // SCALING_FACTOR
+#include "Utils.hpp"               // resources_dir
+
+#include <algorithm>
+#include <limits>
+
+namespace Slic3r {
+
+// Convert one ExPolygon (outer contour + CW holes) into an ImportRegion,
+// mapping each integer Point to plane (u,v) mm via `to_mm`.
+template<class ToMm>
+static ImportRegion expoly_to_region(const ExPolygon& ex, ToMm to_mm)
+{
+    auto contour_pts = [&](const Polygon& poly) {
+        std::vector<Vec2d> c;
+        c.reserve(poly.points.size());
+        for (const Point& p : poly.points)
+            c.push_back(to_mm(p));
+        return c;
+    };
+    ImportRegion region;
+    region.push_back(contour_pts(ex.contour));
+    for (const Polygon& h : ex.holes)
+        region.push_back(contour_pts(h));
+    return region;
+}
+
+// Shift all regions so their common bounding-box centre sits on the origin
+// (Onshape/typical CAD insert places imported art centred on the sketch).
+static void center_regions(ImportRegions& regs)
+{
+    double lo_x =  std::numeric_limits<double>::max();
+    double lo_y =  std::numeric_limits<double>::max();
+    double hi_x = -std::numeric_limits<double>::max();
+    double hi_y = -std::numeric_limits<double>::max();
+    bool any = false;
+    for (const auto& region : regs)
+        for (const auto& contour : region)
+            for (const Vec2d& p : contour) {
+                lo_x = std::min(lo_x, p.x()); hi_x = std::max(hi_x, p.x());
+                lo_y = std::min(lo_y, p.y()); hi_y = std::max(hi_y, p.y());
+                any = true;
+            }
+    if (!any) return;
+    const Vec2d c(0.5 * (lo_x + hi_x), 0.5 * (lo_y + hi_y));
+    for (auto& region : regs)
+        for (auto& contour : region)
+            for (Vec2d& p : contour)
+                p -= c;
+}
+
+static std::string default_font_path()
+{
+    return resources_dir() + "/fonts/HarmonyOS_Sans_SC_Regular.ttf";
+}
+
+ImportRegions text_to_regions(const std::string& utf8, double size_mm,
+                              const std::string& font_path)
+{
+    if (utf8.empty() || size_mm <= 0.0)
+        return {};
+
+    const std::string path = font_path.empty() ? default_font_path() : font_path;
+    std::unique_ptr<Emboss::FontFile> ff = Emboss::create_font_file(path.c_str());
+    if (!ff)
+        return {};
+    Emboss::FontFileWithCache fwc(std::move(ff));
+    if (!fwc.has_value())
+        return {};
+
+    FontProp prop(static_cast<float>(size_mm));   // per_glyph=false
+    HealedExPolygons healed = Emboss::text2shapes(fwc, utf8.c_str(), prop);
+    if (healed.expolygons.empty())
+        return {};
+
+    // Shape points are integers scaled by 1/SHAPE_SCALE in font units;
+    // get_text_shape_scale collapses (size_in_mm / unit_per_em) * SHAPE_SCALE
+    // into a single mm-per-shape-unit factor. FreeType y is up already.
+    const double s = Emboss::get_text_shape_scale(prop, *fwc.font_file);
+    auto to_mm = [s](const Point& p) { return Vec2d(p.x() * s, p.y() * s); };
+
+    ImportRegions regs;
+    regs.reserve(healed.expolygons.size());
+    for (const ExPolygon& ex : healed.expolygons)
+        regs.push_back(expoly_to_region(ex, to_mm));
+
+    center_regions(regs);
+    return regs;
+}
+
+ImportRegions svg_to_regions(const std::string& svg_path, double scale)
+{
+    if (svg_path.empty() || scale <= 0.0)
+        return {};
+
+    NSVGimage_ptr image = nsvgParseFromFile(svg_path, "mm", 96.0f);
+    if (!image)
+        return {};
+
+    // A filled shape that also carries a stroke would import the stroke as a
+    // thick outline band wrapped around the fill (the reported "too large line
+    // width"). For CAD import the fill silhouette is what's wanted, so drop the
+    // stroke on any shape that has a fill; stroke-only line art is kept.
+    for (NSVGshape* s = image->shapes; s != nullptr; s = s->next)
+        if (s->fill.type != NSVG_PAINT_NONE)
+            s->stroke.type = NSVG_PAINT_NONE;
+
+    // tesselation tolerance is in image (mm) scale; 0.3 mm keeps curves smooth
+    // without exploding the contour count. is_y_negative (default) flips SVG's
+    // y-down to the sketch's y-up.
+    NSVGLineParams param(0.3);
+    ExPolygonsWithIds ids = create_shape_with_ids(*image, param);
+
+    // NSVG points are integers scaled by 1/SCALING_FACTOR (param.scale default):
+    // mm = point * SCALING_FACTOR, then the user scale factor.
+    const double s = SCALING_FACTOR * scale;
+    auto to_mm = [s](const Point& p) { return Vec2d(p.x() * s, p.y() * s); };
+
+    ImportRegions regs;
+    for (const ExPolygonsWithId& w : ids)
+        for (const ExPolygon& ex : w.expoly)
+            regs.push_back(expoly_to_region(ex, to_mm));
+
+    center_regions(regs);
+    return regs;
+}
+
+ImportRegions transform_regions(const ImportRegions& src, const Vec2d& offset,
+                                double scale_x, double scale_y)
+{
+    ImportRegions out = src;
+    for (auto& region : out)
+        for (auto& contour : region)
+            for (Vec2d& p : contour)
+                p = Vec2d(p.x() * scale_x + offset.x(), p.y() * scale_y + offset.y());
+    return out;
+}
+
+} // namespace Slic3r
@@ -0,0 +1,37 @@
+#ifndef slic3r_SketchImport_hpp_
+#define slic3r_SketchImport_hpp_
+
+#include "Point.hpp"   // Vec2d
+
+#include <string>
+#include <vector>
+
+namespace Slic3r {
+
+// A rigid imported region: contour[0] = outer loop, contour[1..] = holes;
+// points in plane (u,v) millimetres. The nested vector type matches
+// CadFeature::imported_regions exactly, so results assign directly.
+using ImportRegion  = std::vector<std::vector<Vec2d>>;
+using ImportRegions = std::vector<ImportRegion>;
+
+// Vectorize UTF-8 text into filled regions (mm), centred on the origin.
+// `size_mm` is the cap/line height. `font_path` empty -> a bundled default
+// font (resources/fonts). Returns an empty vector on any failure.
+ImportRegions text_to_regions(const std::string& utf8, double size_mm,
+                              const std::string& font_path = std::string());
+
+// Parse an SVG file's filled paths into regions (mm), centred on the origin.
+// `scale` multiplies the authored size (1.0 = as authored). Returns an empty
+// vector on any failure.
+ImportRegions svg_to_regions(const std::string& svg_path, double scale = 1.0);
+
+// Apply an axis-aligned placement transform to regions:
+//   p -> ( p.x * scale_x + offset.x,  p.y * scale_y + offset.y )
+// Used to move / enlarge / stretch imported art non-destructively (the
+// feature keeps the centred source regions + this transform).
+ImportRegions transform_regions(const ImportRegions& src, const Vec2d& offset,
+                                double scale_x, double scale_y);
+
+} // namespace Slic3r
+
+#endif // slic3r_SketchImport_hpp_
@@ -0,0 +1,120 @@
+#include "SketchInference.hpp"
+
+#include <cmath>
+
+namespace Slic3r {
+
+// Candidate target collected during the scan; we keep the closest within each
+// priority tier and resolve ties by tier then distance.
+namespace {
+struct Cand {
+    InferenceSnap::Kind kind{InferenceSnap::Kind::None};
+    int                 entity{-1};
+    SketchPointRole     role{SketchPointRole::P0};
+    Vec2d               point{0, 0};
+    double              dist{0.0};
+};
+
+// Lower number = higher priority.
+int tier(InferenceSnap::Kind k)
+{
+    switch (k) {
+    case InferenceSnap::Kind::Endpoint: return 0;
+    case InferenceSnap::Kind::Center:   return 1;
+    case InferenceSnap::Kind::Origin:   return 2;
+    case InferenceSnap::Kind::Midpoint: return 3;
+    case InferenceSnap::Kind::OnEdge:   return 4;
+    default:                            return 9;
+    }
+}
+} // namespace
+
+InferenceSnap infer_point_snap(const std::vector<SketchEntity>& entities,
+                               const Vec2d& query, double tol,
+                               bool include_origin)
+{
+    Cand best;
+    best.kind = InferenceSnap::Kind::None;
+    best.point = query;
+
+    auto offer = [&](InferenceSnap::Kind k, int ent, SketchPointRole r, const Vec2d& q) {
+        const double d = (q - query).norm();
+        if (d > tol) return;
+        const bool better = (best.kind == InferenceSnap::Kind::None) ||
+                            (tier(k) < tier(best.kind)) ||
+                            (tier(k) == tier(best.kind) && d < best.dist);
+        if (better) { best.kind = k; best.entity = ent; best.role = r; best.point = q; best.dist = d; }
+    };
+
+    for (size_t i = 0; i < entities.size(); ++i) {
+        const SketchEntity& e = entities[i];
+        const int ei = int(i);
+        switch (e.type) {
+        case SketchEntity::Type::Line: {
+            offer(InferenceSnap::Kind::Endpoint, ei, SketchPointRole::P0, e.p0);
+            offer(InferenceSnap::Kind::Endpoint, ei, SketchPointRole::P1, e.p1);
+            offer(InferenceSnap::Kind::Midpoint, ei, SketchPointRole::P0, 0.5 * (e.p0 + e.p1));
+            // Projection onto the segment interior (PointOnObject candidate).
+            const Vec2d d = e.p1 - e.p0;
+            const double L2 = d.squaredNorm();
+            if (L2 > 1e-12) {
+                double t = (query - e.p0).dot(d) / L2;
+                if (t > 0.02 && t < 0.98)
+                    offer(InferenceSnap::Kind::OnEdge, ei, SketchPointRole::P0, e.p0 + t * d);
+            }
+            break;
+        }
+        case SketchEntity::Type::Arc:
+            offer(InferenceSnap::Kind::Endpoint, ei, SketchPointRole::P0, e.p0);
+            offer(InferenceSnap::Kind::Endpoint, ei, SketchPointRole::P1, e.p1);
+            offer(InferenceSnap::Kind::Center,   ei, SketchPointRole::Center, e.center);
+            break;
+        case SketchEntity::Type::Circle: {
+            offer(InferenceSnap::Kind::Center, ei, SketchPointRole::Center, e.center);
+            // Nearest point on the circle rim (PointOnObject candidate).
+            const Vec2d v = query - e.center;
+            const double n = v.norm();
+            if (n > 1e-9 && e.radius > 1e-9)
+                offer(InferenceSnap::Kind::OnEdge, ei, SketchPointRole::Center,
+                      e.center + v * (e.radius / n));
+            break;
+        }
+        case SketchEntity::Type::Point:
+            offer(InferenceSnap::Kind::Endpoint, ei, SketchPointRole::P0, e.p0);
+            break;
+        case SketchEntity::Type::EllipseArc:
+            offer(InferenceSnap::Kind::Endpoint, ei, SketchPointRole::P0, e.p0);
+            offer(InferenceSnap::Kind::Endpoint, ei, SketchPointRole::P1, e.p1);
+            offer(InferenceSnap::Kind::Center,   ei, SketchPointRole::Center, e.center);
+            break;
+        case SketchEntity::Type::Ellipse:
+            offer(InferenceSnap::Kind::Center, ei, SketchPointRole::Center, e.center);
+            break;
+        case SketchEntity::Type::BSpline:
+            // Endpoints (first/last pole) snap for loop closure.
+            offer(InferenceSnap::Kind::Endpoint, ei, SketchPointRole::P0, e.p0);
+            offer(InferenceSnap::Kind::Endpoint, ei, SketchPointRole::P1, e.p1);
+            break;
+        }
+    }
+
+    if (include_origin)
+        offer(InferenceSnap::Kind::Origin, -1, SketchPointRole::P0, Vec2d(0, 0));
+
+    InferenceSnap r;
+    r.kind = best.kind; r.entity = best.entity; r.role = best.role; r.point = best.point;
+    return r;
+}
+
+std::optional<SketchConstraintType>
+infer_axis_constraint(const Vec2d& anchor, const Vec2d& tip, double ang_tol_rad)
+{
+    const Vec2d d = tip - anchor;
+    if (d.squaredNorm() < 1e-12) return std::nullopt;
+    const double ang = std::atan2(std::abs(d.y()), std::abs(d.x())); // 0=horizontal, pi/2=vertical
+    if (ang <= ang_tol_rad)                 return SketchConstraintType::Horizontal;
+    if (ang >= M_PI / 2.0 - ang_tol_rad)    return SketchConstraintType::Vertical;
+    return std::nullopt;
+}
+
+} // namespace Slic3r
@@ -0,0 +1,44 @@
+#ifndef slic3r_SketchInference_hpp_
+#define slic3r_SketchInference_hpp_
+
+#include "SketchEngine.hpp"
+#include <vector>
+#include <optional>
+#include <cmath>
+
+namespace Slic3r {
+
+// Result of snapping a free cursor point onto the most relevant inference target
+// among the committed sketch entities and the sketch origin. This is the backbone
+// that lets geometry self-constrain as it is drawn: the GUI records the returned
+// target at click time and, once the entity it belongs to exists, emits the
+// matching constraint (Coincident onto an endpoint/centre, Fix onto the origin,
+// PointOnObject onto an edge) so the relation survives a re-solve.
+struct InferenceSnap {
+    enum class Kind { None, Endpoint, Center, Midpoint, OnEdge, Origin };
+    Kind            kind{Kind::None};
+    int             entity{-1};                       // hit entity index (-1 = origin/none)
+    SketchPointRole role{SketchPointRole::P0};         // which point of `entity` (Endpoint/Center)
+    Vec2d           point{0, 0};                       // snapped coordinate (== query when None)
+
+    bool snapped() const { return kind != Kind::None; }
+};
+
+// Snap `query` onto the best inference target within `tol` plane units. Priority,
+// highest first: Endpoint, Center, Origin, Midpoint, OnEdge. Construction entities
+// participate (you constrain to them too). Returns {None, query} when nothing is in
+// range. Pure — no GUI / GL dependencies, so it is unit-testable in libslic3r.
+InferenceSnap infer_point_snap(const std::vector<SketchEntity>& entities,
+                               const Vec2d& query, double tol,
+                               bool include_origin = true);
+
+// Relational inference for an in-progress segment anchor->tip. If its direction is
+// within `ang_tol_rad` of an axis, returns Horizontal or Vertical (the constraint to
+// auto-emit on the committed segment); std::nullopt otherwise. Degenerate (near-zero
+// length) segments return nullopt.
+std::optional<SketchConstraintType>
+infer_axis_constraint(const Vec2d& anchor, const Vec2d& tip, double ang_tol_rad = 3.0 * M_PI / 180.0);
+
+} // namespace Slic3r
+
+#endif // slic3r_SketchInference_hpp_
@@ -0,0 +1,361 @@
+#include "SketchSolver.hpp"
+
+#include <slvs.h>
+
+#include <cmath>
+#include <cstring>
+#include <unordered_map>
+
+namespace Slic3r {
+
+using CT = SketchConstraintType;
+using Role = SketchPointRole;
+
+namespace {
+
+constexpr Slvs_hGroup G_FIXED = 1;   // workplane / reference: held constant
+constexpr Slvs_hGroup G_SK    = 2;   // sketch geometry: the group we solve
+
+// Per-entity slvs handles. p0/p1/center are point2d entity handles; prim is the
+// line/arc/circle entity; rparam is the circle radius param.
+struct Slots {
+    Slvs_hEntity prim{0}, p0{0}, p1{0}, center{0};
+    Slvs_hParam  rparam{0};
+    std::vector<Slvs_hEntity> pts;   // BSpline control points (point2d handles)
+};
+
+struct Build {
+    std::vector<Slvs_Param>      params;
+    std::vector<Slvs_Entity>     ents;
+    std::vector<Slvs_Constraint> cons;
+    Slvs_hParam      ph{0};
+    Slvs_hEntity     eh{0};
+    Slvs_hConstraint ch{0};
+    Slvs_hEntity     wp{0}, normal{0};
+
+    Slvs_hParam  P(Slvs_hGroup g, double v) { params.push_back(Slvs_MakeParam(++ph, g, v)); return ph; }
+    Slvs_hEntity E(Slvs_Entity e)           { ents.push_back(e); return e.h; }
+    Slvs_hEntity pt2d(Slvs_hGroup g, double u, double v)
+        { return E(Slvs_MakePoint2d(++eh, g, wp, P(g, u), P(g, v))); }
+
+    // Generic constraint (entityC unused by Slvs_MakeConstraint — set it manually below).
+    void C(int type, double val, Slvs_hEntity ptA, Slvs_hEntity ptB,
+           Slvs_hEntity eA, Slvs_hEntity eB, Slvs_hEntity eC = 0, int other = 0)
+    {
+        Slvs_Constraint c = Slvs_MakeConstraint(++ch, G_SK, type, wp, val, ptA, ptB, eA, eB);
+        c.entityC = eC;
+        c.other   = other;
+        cons.push_back(c);
+    }
+};
+
+inline int role_idx(Role r) { return int(r); }
+
+} // namespace
+
+static SketchSolveResult solve_impl(std::vector<SketchEntity>& entities,
+                                    const std::vector<SketchEntityConstraintDef>& constraints,
+                                    int dragged_ei, Role dragged_role)
+{
+    SketchSolveResult out;
+    if (constraints.empty()) { out.ok = true; out.dof = -1; return out; }
+
+    Build b;
+
+    // ---- Fixed 2D XY workplane (origin at 0,0,0; identity normal) -------------------
+    Slvs_hEntity origin = b.E(Slvs_MakePoint3d(++b.eh, G_FIXED,
+                              b.P(G_FIXED, 0.0), b.P(G_FIXED, 0.0), b.P(G_FIXED, 0.0)));
+    double qw, qx, qy, qz;
+    Slvs_MakeQuaternion(1, 0, 0,  0, 1, 0,  &qw, &qx, &qy, &qz);
+    b.normal = b.E(Slvs_MakeNormal3d(++b.eh, G_FIXED,
+                   b.P(G_FIXED, qw), b.P(G_FIXED, qx), b.P(G_FIXED, qy), b.P(G_FIXED, qz)));
+    b.wp = b.E(Slvs_MakeWorkplane(++b.eh, G_FIXED, origin, b.normal));
+
+    // ---- Entities -------------------------------------------------------------------
+    std::vector<Slots> slot(entities.size());
+    for (size_t i = 0; i < entities.size(); ++i) {
+        const SketchEntity& e = entities[i];
+        Slots s;
+        switch (e.type) {
+        case SketchEntity::Type::Line:
+            s.p0   = b.pt2d(G_SK, e.p0.x(), e.p0.y());
+            s.p1   = b.pt2d(G_SK, e.p1.x(), e.p1.y());
+            s.prim = b.E(Slvs_MakeLineSegment(++b.eh, G_SK, b.wp, s.p0, s.p1));
+            break;
+        case SketchEntity::Type::Point:
+            s.p0 = b.pt2d(G_SK, e.p0.x(), e.p0.y());
+            break;
+        case SketchEntity::Type::Circle: {
+            s.center = b.pt2d(G_SK, e.center.x(), e.center.y());
+            s.p0     = s.center;                          // p0 mirrors centre for circles
+            s.rparam = b.P(G_SK, e.radius > 1e-9 ? e.radius : 1.0);
+            Slvs_hEntity dist = b.E(Slvs_MakeDistance(++b.eh, G_SK, b.wp, s.rparam));
+            s.prim   = b.E(Slvs_MakeCircle(++b.eh, G_SK, b.wp, s.center, b.normal, dist));
+            break;
+        }
+        case SketchEntity::Type::Arc:
+            s.center = b.pt2d(G_SK, e.center.x(), e.center.y());
+            s.p0     = b.pt2d(G_SK, e.p0.x(), e.p0.y());   // start
+            s.p1     = b.pt2d(G_SK, e.p1.x(), e.p1.y());   // end
+            s.prim   = b.E(Slvs_MakeArcOfCircle(++b.eh, G_SK, b.wp, b.normal, s.center, s.p0, s.p1));
+            break;
+        // libslvs has no conic entity (scope note): register the ellipse's defining
+        // points only (center + arc endpoints) so center/endpoint constraints solve;
+        // the a/b/phi shape params pass through unsolved.
+        case SketchEntity::Type::Ellipse:
+            s.center = b.pt2d(G_SK, e.center.x(), e.center.y());
+            s.p0     = s.center;                          // p0 mirrors centre (circle convention)
+            break;
+        case SketchEntity::Type::EllipseArc:
+            s.center = b.pt2d(G_SK, e.center.x(), e.center.y());
+            s.p0     = b.pt2d(G_SK, e.p0.x(), e.p0.y());   // start
+            s.p1     = b.pt2d(G_SK, e.p1.x(), e.p1.y());   // end
+            break;
+        // No native slvs curve for an arbitrary-degree spline: register the control
+        // poles as point2d so endpoints (and any pole-targeted constraint) solve. The
+        // OCCT curve is rebuilt from the solved poles. p0/p1 mirror first/last pole so
+        // Coincident at the spline ends closes loops just like a Line.
+        case SketchEntity::Type::BSpline:
+            s.pts.reserve(e.ctrl.size());
+            for (const Vec2d& cp : e.ctrl)
+                s.pts.push_back(b.pt2d(G_SK, cp.x(), cp.y()));
+            if (!s.pts.empty()) { s.p0 = s.pts.front(); s.p1 = s.pts.back(); }
+            break;
+        }
+        slot[i] = s;
+    }
+
+    auto valid = [&](int ei) { return ei >= 0 && ei < int(entities.size()); };
+    auto ptOf  = [&](int ei, Role r) -> Slvs_hEntity {
+        if (!valid(ei)) return 0;
+        const Slots& s = slot[ei];
+        switch (r) {
+        case Role::P0:     return s.p0;
+        case Role::P1:     return s.p1;
+        case Role::Center: return s.center ? s.center : s.p0;
+        }
+        return 0;
+    };
+    auto primOf = [&](int ei) -> Slvs_hEntity { return valid(ei) ? slot[ei].prim : 0; };
+    auto coordOf = [&](int ei, Role r) -> Vec2d {
+        if (!valid(ei)) return Vec2d(0, 0);
+        const SketchEntity& e = entities[ei];
+        switch (r) { case Role::P0: return e.p0; case Role::P1: return e.p1; case Role::Center: return e.center; }
+        return e.p0;
+    };
+    // A fixed reference point at (x,y) — used to pin coordinates (Fix / LockX / LockY).
+    auto fixedRef = [&](double x, double y) -> Slvs_hEntity { return b.pt2d(G_FIXED, x, y); };
+
+    // ---- Constraints ----------------------------------------------------------------
+    for (const auto& c : constraints) {
+        // Robustness: never feed libslvs a null handle. A constraint that references an
+        // entity which produced no solver primitive (Point/Ellipse/EllipseArc/BSpline get
+        // no `prim`) or no point for the requested role would make Slvs FindById abort the
+        // whole process. Skip such a constraint instead of crashing.
+        bool ref_ok = true;
+        switch (c.type) {
+        case CT::Coincident: case CT::Horizontal: case CT::Vertical: case CT::Distance:
+            ref_ok = ptOf(c.ea, c.ra) && ptOf(c.eb, c.rb); break;
+        case CT::Concentric:
+            ref_ok = ptOf(c.ea, Role::Center) && ptOf(c.eb, Role::Center); break;
+        case CT::Fix: case CT::LockX: case CT::LockY:
+            ref_ok = ptOf(c.ea, c.ra) != 0; break;
+        case CT::EqualLength: case CT::Parallel: case CT::Perpendicular:
+        case CT::Angle: case CT::Tangent:
+            ref_ok = primOf(c.ea) && primOf(c.eb); break;
+        case CT::Radius: case CT::Diameter:
+            ref_ok = primOf(c.ea) != 0; break;
+        case CT::Midpoint:
+            ref_ok = ptOf(c.ea, c.ra) && primOf(c.eb); break;
+        case CT::Symmetric:
+            ref_ok = ptOf(c.ea, c.ra) && ptOf(c.eb, c.rb) && primOf(c.ec); break;
+        case CT::PointOnLine: case CT::PointOnObject:
+            ref_ok = ptOf(c.ea, c.ra) && primOf(c.eb); break;
+        }
+        if (!ref_ok) continue;
+        switch (c.type) {
+        case CT::Coincident:
+            b.C(SLVS_C_POINTS_COINCIDENT, 0, ptOf(c.ea, c.ra), ptOf(c.eb, c.rb), 0, 0);
+            break;
+        case CT::Concentric:
+            b.C(SLVS_C_POINTS_COINCIDENT, 0, ptOf(c.ea, Role::Center), ptOf(c.eb, Role::Center), 0, 0);
+            break;
+        case CT::Horizontal:
+            b.C(SLVS_C_HORIZONTAL, 0, ptOf(c.ea, c.ra), ptOf(c.eb, c.rb), 0, 0);
+            break;
+        case CT::Vertical:
+            b.C(SLVS_C_VERTICAL, 0, ptOf(c.ea, c.ra), ptOf(c.eb, c.rb), 0, 0);
+            break;
+        case CT::Distance:
+            b.C(SLVS_C_PT_PT_DISTANCE, c.value, ptOf(c.ea, c.ra), ptOf(c.eb, c.rb), 0, 0);
+            break;
+        case CT::Fix: {
+            const Vec2d p = coordOf(c.ea, c.ra);
+            b.C(SLVS_C_POINTS_COINCIDENT, 0, ptOf(c.ea, c.ra), fixedRef(p.x(), p.y()), 0, 0);
+            break;
+        }
+        case CT::LockX: {
+            const Vec2d p = coordOf(c.ea, c.ra);
+            b.C(SLVS_C_VERTICAL, 0, ptOf(c.ea, c.ra), fixedRef(c.value, p.y()), 0, 0);
+            break;
+        }
+        case CT::LockY: {
+            const Vec2d p = coordOf(c.ea, c.ra);
+            b.C(SLVS_C_HORIZONTAL, 0, ptOf(c.ea, c.ra), fixedRef(p.x(), c.value), 0, 0);
+            break;
+        }
+        case CT::EqualLength:
+            b.C(SLVS_C_EQUAL_LENGTH_LINES, 0, 0, 0, primOf(c.ea), primOf(c.eb));
+            break;
+        case CT::Parallel:
+            b.C(SLVS_C_PARALLEL, 0, 0, 0, primOf(c.ea), primOf(c.eb));
+            break;
+        case CT::Perpendicular:
+            b.C(SLVS_C_PERPENDICULAR, 0, 0, 0, primOf(c.ea), primOf(c.eb));
+            break;
+        case CT::Midpoint:
+            b.C(SLVS_C_AT_MIDPOINT, 0, ptOf(c.ea, c.ra), 0, primOf(c.eb), 0);
+            break;
+        case CT::Symmetric:
+            // ptA, ptB symmetric about the axis line (ec).
+            b.C(SLVS_C_SYMMETRIC_LINE, 0, ptOf(c.ea, c.ra), ptOf(c.eb, c.rb), primOf(c.ec), 0);
+            break;
+        case CT::Angle:
+            // model stores radians; slvs angle is in degrees.
+            b.C(SLVS_C_ANGLE, c.value * 180.0 / M_PI, 0, 0, primOf(c.ea), primOf(c.eb));
+            break;
+        case CT::Radius:
+            b.C(SLVS_C_DIAMETER, 2.0 * c.value, 0, 0, primOf(c.ea), 0);
+            break;
+        case CT::Diameter:
+            b.C(SLVS_C_DIAMETER, c.value, 0, 0, primOf(c.ea), 0);
+            break;
+        case CT::Tangent: {
+            const bool aCurve = valid(c.ea) && entities[c.ea].type != SketchEntity::Type::Line;
+            const bool bCurve = valid(c.eb) && entities[c.eb].type != SketchEntity::Type::Line;
+            if (aCurve && bCurve)
+                b.C(SLVS_C_CURVE_CURVE_TANGENT, 0, 0, 0, primOf(c.ea), primOf(c.eb));
+            else {
+                const Slvs_hEntity arc  = aCurve ? primOf(c.ea) : primOf(c.eb);
+                const Slvs_hEntity line = aCurve ? primOf(c.eb) : primOf(c.ea);
+                b.C(SLVS_C_ARC_LINE_TANGENT, 0, 0, 0, arc, line);
+            }
+            break;
+        }
+        case CT::PointOnLine:
+            if (std::abs(c.value) < 1e-9)
+                b.C(SLVS_C_PT_ON_LINE, 0, ptOf(c.ea, c.ra), 0, primOf(c.eb), 0);
+            else
+                b.C(SLVS_C_PT_LINE_DISTANCE, std::abs(c.value), ptOf(c.ea, c.ra), 0, primOf(c.eb), 0);
+            break;
+        case CT::PointOnObject:
+            // Point (ea,ra) lies on entity edge eb: a circle rim -> PT_ON_CIRCLE,
+            // otherwise the segment line -> PT_ON_LINE.
+            if (valid(c.eb) && entities[c.eb].type == SketchEntity::Type::Circle)
+                b.C(SLVS_C_PT_ON_CIRCLE, 0, ptOf(c.ea, c.ra), 0, primOf(c.eb), 0);
+            else
+                b.C(SLVS_C_PT_ON_LINE, 0, ptOf(c.ea, c.ra), 0, primOf(c.eb), 0);
+            break;
+        }
+    }
+
+    // ---- Solve ----------------------------------------------------------------------
+    Slvs_System sys;
+    std::memset(&sys, 0, sizeof(sys));
+    sys.param       = b.params.data();      sys.params      = int(b.params.size());
+    sys.entity      = b.ents.data();        sys.entities    = int(b.ents.size());
+    sys.constraint  = b.cons.data();        sys.constraints = int(b.cons.size());
+    std::vector<Slvs_hConstraint> failed(b.cons.size() + 1, 0);
+    sys.failed = failed.data();
+    sys.faileds = int(failed.size());
+    sys.calculateFaileds = 1;
+
+    // Drag pin: feed the dragged point's two params into sys.dragged[] so the solver
+    // favours keeping that point at the cursor and re-solves the rest around it.
+    if (dragged_ei >= 0) {
+        const Slvs_hEntity h = ptOf(dragged_ei, dragged_role);
+        for (const Slvs_Entity& en : b.ents)
+            if (en.h == h) { sys.dragged[0] = en.param[0]; sys.dragged[1] = en.param[1]; break; }
+    }
+
+    Slvs_Solve(&sys, G_SK);
+
+    out.result = sys.result;
+    out.dof    = sys.dof;
+    out.ok     = (sys.result == SLVS_RESULT_OKAY);
+
+    // Map solved param handles -> values, then read points back.
+    std::unordered_map<Slvs_hParam, double> pv;
+    pv.reserve(sys.params * 2);
+    for (int i = 0; i < sys.params; ++i) pv[sys.param[i].h] = sys.param[i].val;
+    std::unordered_map<Slvs_hEntity, const Slvs_Entity*> byH;
+    byH.reserve(sys.entities * 2);
+    for (int i = 0; i < sys.entities; ++i) byH[sys.entity[i].h] = &sys.entity[i];
+    auto coord = [&](Slvs_hEntity h) -> Vec2d {
+        auto it = byH.find(h);
+        if (it == byH.end()) return Vec2d(0, 0);
+        return Vec2d(pv[it->second->param[0]], pv[it->second->param[1]]);
+    };
+
+    // Map failed constraint handles back to indices into `constraints`.
+    if (!out.ok && sys.faileds > 0) {
+        std::unordered_map<Slvs_hConstraint, int> chToIdx;
+        // constraint handles were assigned in order starting after the fixed group; the
+        // i-th sketch constraint in b.cons has handle = its position. Rebuild by scanning.
+        for (size_t k = 0; k < b.cons.size(); ++k) chToIdx[b.cons[k].h] = int(k);
+        for (int i = 0; i < sys.faileds; ++i) {
+            auto it = chToIdx.find(failed[i]);
+            if (it != chToIdx.end() && it->second < int(constraints.size()))
+                out.bad.push_back(it->second);
+        }
+    }
+
+    // ---- Read solved geometry back --------------------------------------------------
+    for (size_t i = 0; i < entities.size(); ++i) {
+        SketchEntity& e = entities[i];
+        const Slots&  s = slot[i];
+        if (s.p0)     e.p0     = coord(s.p0);
+        if (s.p1)     e.p1     = coord(s.p1);
+        if (s.center) e.center = coord(s.center);
+
+        if (e.type == SketchEntity::Type::BSpline) {
+            for (size_t k = 0; k < s.pts.size() && k < e.ctrl.size(); ++k)
+                e.ctrl[k] = coord(s.pts[k]);
+            if (!e.ctrl.empty()) { e.p0 = e.ctrl.front(); e.p1 = e.ctrl.back(); }
+        } else if (e.type == SketchEntity::Type::Circle) {
+            if (s.rparam) { auto it = pv.find(s.rparam); if (it != pv.end()) e.radius = it->second; }
+            e.p0 = e.center;
+        } else if (e.type == SketchEntity::Type::Arc && s.center) {
+            // Reflow arc angles from solved centre + endpoints, preserving sweep sign.
+            const double old_sweep = e.end_angle - e.start_angle;
+            const double ns = std::atan2(e.p0.y() - e.center.y(), e.p0.x() - e.center.x());
+            const double ne = std::atan2(e.p1.y() - e.center.y(), e.p1.x() - e.center.x());
+            double sweep = ne - ns;
+            const double TWO_PI = 2.0 * M_PI;
+            while (sweep <= -TWO_PI) sweep += TWO_PI;
+            while (sweep >=  TWO_PI) sweep -= TWO_PI;
+            if (old_sweep >= 0.0 && sweep < 0.0) sweep += TWO_PI;
+            if (old_sweep <  0.0 && sweep > 0.0) sweep -= TWO_PI;
+            e.start_angle = ns;
+            e.end_angle   = ns + sweep;
+            e.radius = 0.5 * ((e.p0 - e.center).norm() + (e.p1 - e.center).norm());
+        }
+    }
+
+    return out;
+}
+
+SketchSolveResult sketch_solve(std::vector<SketchEntity>& entities,
+                               const std::vector<SketchEntityConstraintDef>& constraints)
+{
+    return solve_impl(entities, constraints, -1, Role::P0);
+}
+
+SketchSolveResult sketch_solve_drag(std::vector<SketchEntity>& entities,
+                                    const std::vector<SketchEntityConstraintDef>& constraints,
+                                    int dragged_ei, SketchPointRole dragged_role)
+{
+    return solve_impl(entities, constraints, dragged_ei, dragged_role);
+}
+
+} // namespace Slic3r
@@ -0,0 +1,37 @@
+#ifndef slic3r_SketchSolver_hpp_
+#define slic3r_SketchSolver_hpp_
+
+// Bridge from SnapOrca's SketchEntity / SketchEntityConstraintDef model onto the
+// vendored SolveSpace constraint solver (src/libslic3r/slvs, libslvs). Replaces the
+// hand-rolled SketchConstraints: full constraint set, real DoF counting, and
+// over-constrained (bad-constraint) detection. Solves on a fixed 2D XY workplane.
+
+#include "SketchEngine.hpp"
+#include <vector>
+
+namespace Slic3r {
+
+struct SketchSolveResult {
+    bool             ok{false};   // solver converged & consistent
+    int              dof{-1};     // remaining degrees of freedom (>0 under-constrained)
+    int              result{0};   // raw SLVS_RESULT_* code
+    std::vector<int> bad;         // indices (into `constraints`) of conflicting constraints
+};
+
+// Solve `constraints` over `entities` in place (writes solved coordinates back into the
+// entities; arc angles are reflowed preserving sweep direction). No-op success when
+// `constraints` is empty.
+SketchSolveResult sketch_solve(std::vector<SketchEntity>& entities,
+                               const std::vector<SketchEntityConstraintDef>& constraints);
+
+// Drag-aware solve: pins the (dragged_ei, dragged_role) point's parameters via the
+// solver's `dragged[]` priority list so the solver keeps that point where the cursor
+// placed it (caller must have moved it first) and moves the OTHER free geometry to
+// re-satisfy the constraints. dragged_ei < 0 behaves identically to sketch_solve.
+SketchSolveResult sketch_solve_drag(std::vector<SketchEntity>& entities,
+                                    const std::vector<SketchEntityConstraintDef>& constraints,
+                                    int dragged_ei, SketchPointRole dragged_role);
+
+} // namespace Slic3r
+
+#endif
@@ -0,0 +1,95 @@
+#include "ThreadStandards.hpp"
+
+namespace Slic3r {
+
+// Imperial helpers: convert nominal inch diameter / threads-per-inch to mm.
+static constexpr double IN  = 25.4;
+static inline double tpi_pitch(double tpi) { return IN / tpi; }
+
+const std::vector<ThreadSpec>& thread_standards()
+{
+    using S = ThreadSpec::Series;
+    static const std::vector<ThreadSpec> table = {
+        // --- ISO metric, coarse pitch (ISO 261 preferred series) ---
+        {"M1",    1.0,  0.25, S::MetricCoarse},
+        {"M1.2",  1.2,  0.25, S::MetricCoarse},
+        {"M1.6",  1.6,  0.35, S::MetricCoarse},
+        {"M2",    2.0,  0.40, S::MetricCoarse},
+        {"M2.5",  2.5,  0.45, S::MetricCoarse},
+        {"M3",    3.0,  0.50, S::MetricCoarse},
+        {"M4",    4.0,  0.70, S::MetricCoarse},
+        {"M5",    5.0,  0.80, S::MetricCoarse},
+        {"M6",    6.0,  1.00, S::MetricCoarse},
+        {"M8",    8.0,  1.25, S::MetricCoarse},
+        {"M10",  10.0,  1.50, S::MetricCoarse},
+        {"M12",  12.0,  1.75, S::MetricCoarse},
+        {"M14",  14.0,  2.00, S::MetricCoarse},
+        {"M16",  16.0,  2.00, S::MetricCoarse},
+        {"M20",  20.0,  2.50, S::MetricCoarse},
+        {"M24",  24.0,  3.00, S::MetricCoarse},
+        {"M30",  30.0,  3.50, S::MetricCoarse},
+        {"M36",  36.0,  4.00, S::MetricCoarse},
+        {"M42",  42.0,  4.50, S::MetricCoarse},
+        {"M48",  48.0,  5.00, S::MetricCoarse},
+        {"M56",  56.0,  5.50, S::MetricCoarse},
+        {"M64",  64.0,  6.00, S::MetricCoarse},
+
+        // --- ISO metric, common fine pitches (ISO 261 fine series) ---
+        {"M8x1",      8.0,  1.00, S::MetricFine},
+        {"M10x1.25", 10.0,  1.25, S::MetricFine},
+        {"M10x1",    10.0,  1.00, S::MetricFine},
+        {"M12x1.5",  12.0,  1.50, S::MetricFine},
+        {"M12x1.25", 12.0,  1.25, S::MetricFine},
+        {"M16x1.5",  16.0,  1.50, S::MetricFine},
+        {"M20x1.5",  20.0,  1.50, S::MetricFine},
+        {"M24x2",    24.0,  2.00, S::MetricFine},
+
+        // --- Unified National Coarse (UTS / ASME B1.1) ---
+        {"#1-64 UNC",   0.073 * IN, tpi_pitch(64), S::UNC},
+        {"#2-56 UNC",   0.086 * IN, tpi_pitch(56), S::UNC},
+        {"#3-48 UNC",   0.099 * IN, tpi_pitch(48), S::UNC},
+        {"#4-40 UNC",   0.112 * IN, tpi_pitch(40), S::UNC},
+        {"#5-40 UNC",   0.125 * IN, tpi_pitch(40), S::UNC},
+        {"#6-32 UNC",   0.138 * IN, tpi_pitch(32), S::UNC},
+        {"#8-32 UNC",   0.164 * IN, tpi_pitch(32), S::UNC},
+        {"#10-24 UNC",  0.190 * IN, tpi_pitch(24), S::UNC},
+        {"#12-24 UNC",  0.216 * IN, tpi_pitch(24), S::UNC},
+        {"1/4-20 UNC",  0.250 * IN, tpi_pitch(20), S::UNC},
+        {"5/16-18 UNC", 0.3125 * IN, tpi_pitch(18), S::UNC},
+        {"3/8-16 UNC",  0.375 * IN, tpi_pitch(16), S::UNC},
+        {"7/16-14 UNC", 0.4375 * IN, tpi_pitch(14), S::UNC},
+        {"1/2-13 UNC",  0.500 * IN, tpi_pitch(13), S::UNC},
+        {"9/16-12 UNC", 0.5625 * IN, tpi_pitch(12), S::UNC},
+        {"5/8-11 UNC",  0.625 * IN, tpi_pitch(11), S::UNC},
+        {"3/4-10 UNC",  0.750 * IN, tpi_pitch(10), S::UNC},
+        {"7/8-9 UNC",   0.875 * IN, tpi_pitch(9),  S::UNC},
+        {"1-8 UNC",     1.000 * IN, tpi_pitch(8),  S::UNC},
+
+        // --- Unified National Fine (UTS / ASME B1.1) ---
+        {"#2-64 UNF",   0.086 * IN, tpi_pitch(64), S::UNF},
+        {"#4-48 UNF",   0.112 * IN, tpi_pitch(48), S::UNF},
+        {"#6-40 UNF",   0.138 * IN, tpi_pitch(40), S::UNF},
+        {"#8-36 UNF",   0.164 * IN, tpi_pitch(36), S::UNF},
+        {"#10-32 UNF",  0.190 * IN, tpi_pitch(32), S::UNF},
+        {"1/4-28 UNF",  0.250 * IN, tpi_pitch(28), S::UNF},
+        {"5/16-24 UNF", 0.3125 * IN, tpi_pitch(24), S::UNF},
+        {"3/8-24 UNF",  0.375 * IN, tpi_pitch(24), S::UNF},
+        {"7/16-20 UNF", 0.4375 * IN, tpi_pitch(20), S::UNF},
+        {"1/2-20 UNF",  0.500 * IN, tpi_pitch(20), S::UNF},
+        {"9/16-18 UNF", 0.5625 * IN, tpi_pitch(18), S::UNF},
+        {"5/8-18 UNF",  0.625 * IN, tpi_pitch(18), S::UNF},
+        {"3/4-16 UNF",  0.750 * IN, tpi_pitch(16), S::UNF},
+        {"1-12 UNF",    1.000 * IN, tpi_pitch(12), S::UNF},
+    };
+    return table;
+}
+
+const ThreadSpec* find_thread_standard(const std::string& name)
+{
+    for (const ThreadSpec& s : thread_standards())
+        if (s.name == name)
+            return &s;
+    return nullptr;
+}
+
+} // namespace Slic3r
@@ -0,0 +1,39 @@
+#ifndef slic3r_ThreadStandards_hpp_
+#define slic3r_ThreadStandards_hpp_
+
+#include <string>
+#include <vector>
+
+namespace Slic3r {
+
+// Canonical mechanical thread specifications (ISO metric + Unified imperial).
+// All dimensions are stored in millimetres so the CAD kernel can consume them
+// directly. The profile is the common 60deg V shared by ISO 261/965 and ASME
+// B1.1 (UTS), so the cut/ridge depth used by the Design-tab Thread tool is the
+// basic external thread height h = 0.6134 * pitch, and the internal (tapped)
+// minor diameter is D1 = D - 1.0825 * pitch (= D - 2*5H/8).
+struct ThreadSpec {
+    enum class Series { MetricCoarse, MetricFine, UNC, UNF };
+
+    std::string name;              // designation, e.g. "M6", "1/4-20 UNC"
+    double      major_diameter_mm; // nominal (crest) diameter
+    double      pitch_mm;          // axial advance per turn
+    Series      series;
+
+    // 60deg basic external thread height (radial crest-to-root engagement).
+    double thread_depth_mm() const { return 0.6134 * pitch_mm; }
+    // Internal/tapped minor (tap-drill) diameter for the same nominal thread.
+    double minor_diameter_mm() const { return major_diameter_mm - 1.0825 * pitch_mm; }
+
+    bool imperial() const { return series == Series::UNC || series == Series::UNF; }
+};
+
+// Full ordered table (metric coarse, metric fine, UNC, UNF) for GUI listing.
+const std::vector<ThreadSpec>& thread_standards();
+
+// Exact case-sensitive designation lookup; nullptr if not a known standard.
+const ThreadSpec* find_thread_standard(const std::string& name);
+
+} // namespace Slic3r
+
+#endif
@@ -0,0 +1,30 @@
+# Vendored SolveSpace geometric constraint solver (libslvs), isolated solver core.
+# Source: github.com/JacobStoren/SolveSpaceLib (extraction of solvespace.com libslvs).
+# GPLv3 — compatible with this AGPL fork. Built as a self-contained STATIC lib; only
+# include/slvs.h (+ SolveSpaceSystem.h C++ wrapper) is exposed to libslic3r.
+# No external deps: it ships its own dense linear solver (no Eigen).
+
+add_library(libslvs STATIC
+    constrainteq.cpp
+    entity.cpp
+    expr.cpp
+    system.cpp
+    util.cpp
+    platform/unixutil.cpp
+    lib.cpp
+    SolveSpaceSystem.cpp)
+
+target_compile_definitions(libslvs PRIVATE -DLIBRARY)
+
+# Public API headers (include/slvs.h, include/SolveSpaceSystem.h) propagate to consumers;
+# the internal solvespace headers stay PRIVATE so they never leak into libslic3r TUs.
+target_include_directories(libslvs
+    PUBLIC  ${CMAKE_CURRENT_SOURCE_DIR}/include
+    PRIVATE ${CMAKE_CURRENT_SOURCE_DIR})
+
+# libslic3r is linked into shared targets → PIC required. Silence warnings for this
+# vendored code (it predates the project's -Wall/-Werror=return-type cleanliness).
+set_target_properties(libslvs PROPERTIES POSITION_INDEPENDENT_CODE ON)
+if (CMAKE_CXX_COMPILER_ID STREQUAL "GNU" OR CMAKE_CXX_COMPILER_ID MATCHES "Clang")
+    target_compile_options(libslvs PRIVATE -w -fno-strict-aliasing)
+endif()
@@ -0,0 +1,675 @@
+
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+
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+
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+possible use to the public, the best way to achieve this is to make it
+free software which everyone can redistribute and change under these terms.
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+    it under the terms of the GNU General Public License as published by
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+
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+    but WITHOUT ANY WARRANTY; without even the implied warranty of
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+    along with this program.  If not, see <http://www.gnu.org/licenses/>.
+
+Also add information on how to contact you by electronic and paper mail.
+
+  If the program does terminal interaction, make it output a short
+notice like this when it starts in an interactive mode:
+
+    <program>  Copyright (C) <year>  <name of author>
+    This program comes with ABSOLUTELY NO WARRANTY; for details type `show w'.
+    This is free software, and you are welcome to redistribute it
+    under certain conditions; type `show c' for details.
+
+The hypothetical commands `show w' and `show c' should show the appropriate
+parts of the General Public License.  Of course, your program's commands
+might be different; for a GUI interface, you would use an "about box".
+
+  You should also get your employer (if you work as a programmer) or school,
+if any, to sign a "copyright disclaimer" for the program, if necessary.
+For more information on this, and how to apply and follow the GNU GPL, see
+<http://www.gnu.org/licenses/>.
+
+  The GNU General Public License does not permit incorporating your program
+into proprietary programs.  If your program is a subroutine library, you
+may consider it more useful to permit linking proprietary applications with
+the library.  If this is what you want to do, use the GNU Lesser General
+Public License instead of this License.  But first, please read
+<http://www.gnu.org/philosophy/why-not-lgpl.html>.
@@ -0,0 +1,177 @@
+
+#define EXPORT_DLL
+#include "SolveSpaceSystem.h"
+#include <assert.h>
+
+
+
+//--------------------------------------------------------------------------------------------------
+/// 
+//--------------------------------------------------------------------------------------------------
+SolveSpaceSystem::SolveSpaceSystem()
+    : m_paramsMemory     (new std::vector<Slvs_Param>       ())
+    , m_entityMemory      (new std::vector<Slvs_Entity>     ())
+    , m_constraintMemory  (new std::vector<Slvs_Constraint> ())
+    , m_failedConstrMemory(new std::vector<Slvs_hConstraint>())
+
+{
+    m_paramsMemory    ->reserve(100);
+    m_entityMemory    ->reserve(100);
+    m_constraintMemory->reserve(100);
+}
+
+//--------------------------------------------------------------------------------------------------
+/// 
+//--------------------------------------------------------------------------------------------------
+Slvs_hParam SolveSpaceSystem::addParam(Slvs_Param parameter)
+{
+
+    parameter.h = static_cast<Slvs_hParam>(m_paramsMemory->size()+1);
+    m_paramsMemory->push_back(parameter);
+
+    m_slvsSystem.param  =  m_paramsMemory->data();
+    m_slvsSystem.params =  static_cast<int>(m_paramsMemory->size());
+
+    return parameter.h;
+}
+
+//--------------------------------------------------------------------------------------------------
+/// 
+//--------------------------------------------------------------------------------------------------
+Slvs_hEntity SolveSpaceSystem::addEntity(Slvs_Entity entity)
+{
+    entity.h = static_cast<Slvs_hEntity>(m_entityMemory->size()+1);
+    m_entityMemory->push_back(entity);
+
+    m_slvsSystem.entity   =  m_entityMemory->data();
+    m_slvsSystem.entities = static_cast<int>(m_entityMemory->size());
+
+    return entity.h;
+}
+
+//--------------------------------------------------------------------------------------------------
+/// 
+//--------------------------------------------------------------------------------------------------
+Slvs_hConstraint SolveSpaceSystem::addConstr(Slvs_Constraint constr)
+{
+    constr.h = static_cast<Slvs_hConstraint>(m_constraintMemory->size()+1);
+    m_constraintMemory->push_back(constr);
+
+    m_slvsSystem.constraint  =  m_constraintMemory->data();
+    m_slvsSystem.constraints = static_cast<int>(m_constraintMemory->size());
+
+    return constr.h;
+}
+
+//--------------------------------------------------------------------------------------------------
+/// 
+//--------------------------------------------------------------------------------------------------
+SolveSpaceSystem::ResultStatus SolveSpaceSystem::solve(Slvs_hGroup groupId, bool reportFailedConstraints /*= true*/)
+{
+    m_failedConstrMemory->resize(m_constraintMemory->size());
+
+    m_slvsSystem.failed  =  m_failedConstrMemory->data();
+    m_slvsSystem.faileds = static_cast<int>(m_failedConstrMemory->size());
+
+    m_slvsSystem.calculateFaileds = reportFailedConstraints;
+
+    Slvs_Solve(&m_slvsSystem, groupId);
+
+    m_failedConstrMemory->resize(m_slvsSystem.faileds);
+
+    return static_cast<ResultStatus>(m_slvsSystem.result);
+}
+
+//--------------------------------------------------------------------------------------------------
+/// 
+//--------------------------------------------------------------------------------------------------
+double SolveSpaceSystem::parameterValue(Slvs_hParam paramId)
+{
+    return (*m_paramsMemory)[paramId-1].val;
+}
+
+//--------------------------------------------------------------------------------------------------
+/// 
+//--------------------------------------------------------------------------------------------------
+void SolveSpaceSystem::setParameterValue(Slvs_hParam paramId, double value)
+{
+    (*m_paramsMemory)[paramId-1].val = value;
+}
+
+//--------------------------------------------------------------------------------------------------
+/// 
+//--------------------------------------------------------------------------------------------------
+std::tuple< std::valarray<double>,
+    std::valarray<double>,
+    std::valarray<double> > SolveSpaceSystem::orientationMx(Slvs_hEntity normalIn3dEntityId)
+{
+    Slvs_Entity e_CS = (*m_entityMemory)[normalIn3dEntityId -1];
+    if ( e_CS.type == SLVS_E_NORMAL_IN_3D )
+    {
+        std::valarray<double> quat ={ 0.0, 0.0, 0.0, 0.0 };
+        quat[0] =  parameterValue(e_CS.param[0]);
+        quat[1] =  parameterValue(e_CS.param[1]);
+        quat[2] =  parameterValue(e_CS.param[2]);
+        quat[3] =  parameterValue(e_CS.param[3]);
+        std::valarray<double> Ex ={ 0.0,0.0,0.0 };
+        std::valarray<double> Ey ={ 0.0,0.0,0.0 };
+        std::valarray<double> Ez ={ 0.0,0.0,0.0 };
+
+        Slvs_QuaternionU(quat[0], quat[1], quat[2], quat[3],
+                         &Ex[0], &Ex[1], &Ex[2]);
+        Slvs_QuaternionV(quat[0], quat[1], quat[2], quat[3],
+                         &Ey[0], &Ey[1], &Ey[2]);
+        Slvs_QuaternionN(quat[0], quat[1], quat[2], quat[3],
+                         &Ez[0], &Ez[1], &Ez[2]);
+
+        return std::make_tuple(Ex, Ey, Ez);
+    }
+    assert(false);
+    return std::make_tuple(std::valarray<double>(), std::valarray<double>(), std::valarray<double>());
+}
+
+//--------------------------------------------------------------------------------------------------
+/// 
+//--------------------------------------------------------------------------------------------------
+std::valarray<double> SolveSpaceSystem::global3DPos(Slvs_hEntity pointEntityId)
+{
+    std::valarray<double> point ={ 0.0,0.0,0.0 };
+
+    Slvs_Entity pointEntity = (*m_entityMemory)[pointEntityId -1];
+    if ( pointEntity.type == SLVS_E_POINT_IN_2D )
+    {
+        std::valarray<double> locPoint ={ 0.0,0.0,0.0 };
+        locPoint[0] = parameterValue(pointEntity.param[0]);
+        locPoint[1] = parameterValue(pointEntity.param[1]);
+
+        Slvs_Entity e_Plane = (*m_entityMemory)[pointEntity.wrkpl - 1];
+        std::valarray<double> origin = global3DPos(e_Plane.point[0]);
+        auto mx = orientationMx(e_Plane.normal);
+        point = origin + std::get<0>(mx)*locPoint[0] + std::get<1>(mx)*locPoint[1];
+
+    }
+    else if ( pointEntity.type == SLVS_E_POINT_IN_3D )
+    {
+        point[0] = parameterValue(pointEntity.param[0]);
+        point[1] = parameterValue(pointEntity.param[1]);
+        point[2] = parameterValue(pointEntity.param[2]);
+    }
+
+    return point;
+}
+
+//--------------------------------------------------------------------------------------------------
+/// 
+//--------------------------------------------------------------------------------------------------
+Slvs_Constraint& SolveSpaceSystem::constraint(Slvs_hConstraint constraintId)
+{
+    return (*m_constraintMemory)[constraintId-1];
+}
+
+//--------------------------------------------------------------------------------------------------
+/// 
+//--------------------------------------------------------------------------------------------------
+ std::vector<Slvs_hConstraint> SolveSpaceSystem::failedConstraints() const
+{
+    return (*m_failedConstrMemory);
+}
@@ -0,0 +1,799 @@
+//-----------------------------------------------------------------------------
+// Given a constraint, generate one or more equations in our symbolic algebra
+// system to represent that constraint; also various geometric helper
+// functions for that.
+//
+// Copyright 2008-2013 Jonathan Westhues.
+//-----------------------------------------------------------------------------
+#include "solvespace.h"
+
+const hConstraint ConstraintBase::NO_CONSTRAINT = { 0 };
+
+bool ConstraintBase::HasLabel() const {
+    switch(type) {
+        case Type::PT_LINE_DISTANCE:
+        case Type::PT_PLANE_DISTANCE:
+        case Type::PT_FACE_DISTANCE:
+        case Type::PT_PT_DISTANCE:
+        case Type::PROJ_PT_DISTANCE:
+        case Type::DIAMETER:
+        case Type::LENGTH_RATIO:
+        case Type::LENGTH_DIFFERENCE:
+        case Type::ANGLE:
+        case Type::COMMENT:
+            return true;
+
+        default:
+            return false;
+    }
+}
+
+ExprVector ConstraintBase::VectorsParallel3d(ExprVector a, ExprVector b, hParam p) {
+    return a.Minus(b.ScaledBy(Expr::From(p)));
+}
+
+Expr *ConstraintBase::PointLineDistance(hEntity wrkpl, hEntity hpt, hEntity hln)
+{
+    EntityBase *ln = SK.GetEntity(hln);
+    EntityBase *a = SK.GetEntity(ln->point[0]);
+    EntityBase *b = SK.GetEntity(ln->point[1]);
+
+    EntityBase *p = SK.GetEntity(hpt);
+
+    if(wrkpl.v == EntityBase::FREE_IN_3D.v) {
+        ExprVector ep = p->PointGetExprs();
+
+        ExprVector ea = a->PointGetExprs();
+        ExprVector eb = b->PointGetExprs();
+        ExprVector eab = ea.Minus(eb);
+        Expr *m = eab.Magnitude();
+
+        return ((eab.Cross(ea.Minus(ep))).Magnitude())->Div(m);
+    } else {
+        Expr *ua, *va, *ub, *vb;
+        a->PointGetExprsInWorkplane(wrkpl, &ua, &va);
+        b->PointGetExprsInWorkplane(wrkpl, &ub, &vb);
+
+        Expr *du = ua->Minus(ub);
+        Expr *dv = va->Minus(vb);
+
+        Expr *u, *v;
+        p->PointGetExprsInWorkplane(wrkpl, &u, &v);
+
+        Expr *m = ((du->Square())->Plus(dv->Square()))->Sqrt();
+
+        Expr *proj = (dv->Times(ua->Minus(u)))->Minus(
+                     (du->Times(va->Minus(v))));
+
+        return proj->Div(m);
+    }
+}
+
+Expr *ConstraintBase::PointPlaneDistance(ExprVector p, hEntity hpl) {
+    ExprVector n;
+    Expr *d;
+    SK.GetEntity(hpl)->WorkplaneGetPlaneExprs(&n, &d);
+    return (p.Dot(n))->Minus(d);
+}
+
+Expr *ConstraintBase::Distance(hEntity wrkpl, hEntity hpa, hEntity hpb) {
+    EntityBase *pa = SK.GetEntity(hpa);
+    EntityBase *pb = SK.GetEntity(hpb);
+    ssassert(pa->IsPoint() && pb->IsPoint(),
+             "Expected two points to measure projected distance between");
+
+    if(wrkpl.v == EntityBase::FREE_IN_3D.v) {
+        // This is true distance
+        ExprVector ea, eb, eab;
+        ea = pa->PointGetExprs();
+        eb = pb->PointGetExprs();
+        eab = ea.Minus(eb);
+
+        return eab.Magnitude();
+    } else {
+        // This is projected distance, in the given workplane.
+        Expr *au, *av, *bu, *bv;
+
+        pa->PointGetExprsInWorkplane(wrkpl, &au, &av);
+        pb->PointGetExprsInWorkplane(wrkpl, &bu, &bv);
+
+        Expr *du = au->Minus(bu);
+        Expr *dv = av->Minus(bv);
+
+        return ((du->Square())->Plus(dv->Square()))->Sqrt();
+    }
+}
+
+//-----------------------------------------------------------------------------
+// Return the cosine of the angle between two vectors. If a workplane is
+// specified, then it's the cosine of their projections into that workplane.
+//-----------------------------------------------------------------------------
+Expr *ConstraintBase::DirectionCosine(hEntity wrkpl,
+                                      ExprVector ae, ExprVector be)
+{
+    if(wrkpl.v == EntityBase::FREE_IN_3D.v) {
+        Expr *mags = (ae.Magnitude())->Times(be.Magnitude());
+        return (ae.Dot(be))->Div(mags);
+    } else {
+        EntityBase *w = SK.GetEntity(wrkpl);
+        ExprVector u = w->Normal()->NormalExprsU();
+        ExprVector v = w->Normal()->NormalExprsV();
+        Expr *ua = u.Dot(ae);
+        Expr *va = v.Dot(ae);
+        Expr *ub = u.Dot(be);
+        Expr *vb = v.Dot(be);
+        Expr *maga = (ua->Square()->Plus(va->Square()))->Sqrt();
+        Expr *magb = (ub->Square()->Plus(vb->Square()))->Sqrt();
+        Expr *dot = (ua->Times(ub))->Plus(va->Times(vb));
+        return dot->Div(maga->Times(magb));
+    }
+}
+
+ExprVector ConstraintBase::PointInThreeSpace(hEntity workplane,
+                                             Expr *u, Expr *v)
+{
+    EntityBase *w = SK.GetEntity(workplane);
+
+    ExprVector ub = w->Normal()->NormalExprsU();
+    ExprVector vb = w->Normal()->NormalExprsV();
+    ExprVector ob = w->WorkplaneGetOffsetExprs();
+
+    return (ub.ScaledBy(u)).Plus(vb.ScaledBy(v)).Plus(ob);
+}
+
+void ConstraintBase::ModifyToSatisfy() {
+    if(type == Type::ANGLE) {
+        Vector a = SK.GetEntity(entityA)->VectorGetNum();
+        Vector b = SK.GetEntity(entityB)->VectorGetNum();
+        if(other) a = a.ScaledBy(-1);
+        if(workplane.v != EntityBase::FREE_IN_3D.v) {
+            a = a.ProjectVectorInto(workplane);
+            b = b.ProjectVectorInto(workplane);
+        }
+        double c = (a.Dot(b))/(a.Magnitude() * b.Magnitude());
+        valA = acos(c)*180/PI;
+    } else if(type == Type::PT_ON_LINE) {
+        EntityBase *eln = SK.GetEntity(entityA);
+        EntityBase *ea = SK.GetEntity(eln->point[0]);
+        EntityBase *eb = SK.GetEntity(eln->point[1]);
+        EntityBase *ep = SK.GetEntity(ptA);
+        ExprVector exp = ep->PointGetExprsInWorkplane(workplane);
+        ExprVector exa = ea->PointGetExprsInWorkplane(workplane);
+        ExprVector exb = eb->PointGetExprsInWorkplane(workplane);
+        ExprVector exba = exb.Minus(exa);
+        SK.GetParam(valP)->val = exba.Dot(exp.Minus(exa))->Eval() / exba.Dot(exba)->Eval();
+    } else {
+        // We'll fix these ones up by looking at their symbolic equation;
+        // that means no extra work.
+        IdList<Equation,hEquation> l = {};
+        // Generate the equations even if this is a reference dimension
+        GenerateEquations(&l, /*forReference=*/true);
+        ssassert(l.n == 1, "Expected constraint to generate a single equation");
+
+        // These equations are written in the form f(...) - d = 0, where
+        // d is the value of the valA.
+        valA += (l.elem[0].e)->Eval();
+
+        l.Clear();
+    }
+}
+
+void ConstraintBase::AddEq(IdList<Equation,hEquation> *l, Expr *expr, int index) const
+{
+    Equation eq;
+    eq.e = expr;
+    eq.h = h.equation(index);
+    l->Add(&eq);
+}
+
+void ConstraintBase::AddEq(IdList<Equation,hEquation> *l, const ExprVector &v,
+                           int baseIndex) const {
+    AddEq(l, v.x, baseIndex);
+    AddEq(l, v.y, baseIndex + 1);
+    if(workplane.v == EntityBase::FREE_IN_3D.v) {
+        AddEq(l, v.z, baseIndex + 2);
+    }
+}
+
+void ConstraintBase::Generate(IdList<Param,hParam> *l) {
+    switch(type) {
+        case Type::PARALLEL:
+        case Type::CUBIC_LINE_TANGENT:
+            // Add new parameter only when we operate in 3d space
+            if(workplane.v != EntityBase::FREE_IN_3D.v) break;
+            // fallthrough
+        case Type::SAME_ORIENTATION:
+        case Type::PT_ON_LINE: {
+            Param p = {};
+            valP = h.param(0);
+            p.h = valP;
+            l->Add(&p);
+            break;
+        }
+
+        default:
+            break;
+    }
+}
+
+void ConstraintBase::GenerateEquations(IdList<Equation,hEquation> *l,
+                                       bool forReference) const {
+    if(reference && !forReference) return;
+
+    Expr *exA = Expr::From(valA);
+    switch(type) {
+        case Type::PT_PT_DISTANCE:
+            AddEq(l, Distance(workplane, ptA, ptB)->Minus(exA), 0);
+            return;
+
+        case Type::PROJ_PT_DISTANCE: {
+            ExprVector pA = SK.GetEntity(ptA)->PointGetExprs(),
+                       pB = SK.GetEntity(ptB)->PointGetExprs(),
+                       dp = pB.Minus(pA);
+
+            ExprVector pp = SK.GetEntity(entityA)->VectorGetExprs();
+            pp = pp.WithMagnitude(Expr::From(1.0));
+
+            AddEq(l, (dp.Dot(pp))->Minus(exA), 0);
+            return;
+        }
+
+        case Type::PT_LINE_DISTANCE:
+            AddEq(l,
+                PointLineDistance(workplane, ptA, entityA)->Minus(exA), 0);
+            return;
+
+        case Type::PT_PLANE_DISTANCE: {
+            ExprVector pt = SK.GetEntity(ptA)->PointGetExprs();
+            AddEq(l, (PointPlaneDistance(pt, entityA))->Minus(exA), 0);
+            return;
+        }
+
+        case Type::PT_FACE_DISTANCE: {
+            ExprVector pt = SK.GetEntity(ptA)->PointGetExprs();
+            EntityBase *f = SK.GetEntity(entityA);
+            ExprVector p0 = f->FaceGetPointExprs();
+            ExprVector n = f->FaceGetNormalExprs();
+            AddEq(l, (pt.Minus(p0)).Dot(n)->Minus(exA), 0);
+            return;
+        }
+
+        case Type::EQUAL_LENGTH_LINES: {
+            EntityBase *a = SK.GetEntity(entityA);
+            EntityBase *b = SK.GetEntity(entityB);
+            AddEq(l, Distance(workplane, a->point[0], a->point[1])->Minus(
+                     Distance(workplane, b->point[0], b->point[1])), 0);
+            return;
+        }
+
+        // These work on distance squared, since the pt-line distances are
+        // signed, and we want the absolute value.
+        case Type::EQ_LEN_PT_LINE_D: {
+            EntityBase *forLen = SK.GetEntity(entityA);
+            Expr *d1 = Distance(workplane, forLen->point[0], forLen->point[1]);
+            Expr *d2 = PointLineDistance(workplane, ptA, entityB);
+            AddEq(l, (d1->Square())->Minus(d2->Square()), 0);
+            return;
+        }
+        case Type::EQ_PT_LN_DISTANCES: {
+            Expr *d1 = PointLineDistance(workplane, ptA, entityA);
+            Expr *d2 = PointLineDistance(workplane, ptB, entityB);
+            AddEq(l, (d1->Square())->Minus(d2->Square()), 0);
+            return;
+        }
+
+        case Type::LENGTH_RATIO: {
+            EntityBase *a = SK.GetEntity(entityA);
+            EntityBase *b = SK.GetEntity(entityB);
+            Expr *la = Distance(workplane, a->point[0], a->point[1]);
+            Expr *lb = Distance(workplane, b->point[0], b->point[1]);
+            AddEq(l, (la->Div(lb))->Minus(exA), 0);
+            return;
+        }
+
+        case Type::LENGTH_DIFFERENCE: {
+            EntityBase *a = SK.GetEntity(entityA);
+            EntityBase *b = SK.GetEntity(entityB);
+            Expr *la = Distance(workplane, a->point[0], a->point[1]);
+            Expr *lb = Distance(workplane, b->point[0], b->point[1]);
+            AddEq(l, (la->Minus(lb))->Minus(exA), 0);
+            return;
+        }
+
+        case Type::DIAMETER: {
+            EntityBase *circle = SK.GetEntity(entityA);
+            Expr *r = circle->CircleGetRadiusExpr();
+            AddEq(l, (r->Times(Expr::From(2)))->Minus(exA), 0);
+            return;
+        }
+
+        case Type::EQUAL_RADIUS: {
+            EntityBase *c1 = SK.GetEntity(entityA);
+            EntityBase *c2 = SK.GetEntity(entityB);
+            AddEq(l, (c1->CircleGetRadiusExpr())->Minus(
+                      c2->CircleGetRadiusExpr()), 0);
+            return;
+        }
+
+        case Type::EQUAL_LINE_ARC_LEN: {
+            EntityBase *line = SK.GetEntity(entityA),
+                       *arc  = SK.GetEntity(entityB);
+
+            // Get the line length
+            ExprVector l0 = SK.GetEntity(line->point[0])->PointGetExprs(),
+                       l1 = SK.GetEntity(line->point[1])->PointGetExprs();
+            Expr *ll = (l1.Minus(l0)).Magnitude();
+
+            // And get the arc radius, and the cosine of its angle
+            EntityBase *ao = SK.GetEntity(arc->point[0]),
+                       *as = SK.GetEntity(arc->point[1]),
+                       *af = SK.GetEntity(arc->point[2]);
+
+            ExprVector aos = (as->PointGetExprs()).Minus(ao->PointGetExprs()),
+                       aof = (af->PointGetExprs()).Minus(ao->PointGetExprs());
+            Expr *r = aof.Magnitude();
+
+            ExprVector n = arc->Normal()->NormalExprsN();
+            ExprVector u = aos.WithMagnitude(Expr::From(1.0));
+            ExprVector v = n.Cross(u);
+            // so in our new csys, we start at (1, 0, 0)
+            Expr *costheta = aof.Dot(u)->Div(r);
+            Expr *sintheta = aof.Dot(v)->Div(r);
+
+            double thetas, thetaf, dtheta;
+            arc->ArcGetAngles(&thetas, &thetaf, &dtheta);
+            Expr *theta;
+            if(dtheta < 3*PI/4) {
+                theta = costheta->ACos();
+            } else if(dtheta < 5*PI/4) {
+                // As the angle crosses pi, cos theta is not invertible;
+                // so use the sine to stop blowing up
+                theta = Expr::From(PI)->Minus(sintheta->ASin());
+            } else {
+                theta = (Expr::From(2*PI))->Minus(costheta->ACos());
+            }
+
+            // And write the equation; r*theta = L
+            AddEq(l, (r->Times(theta))->Minus(ll), 0);
+            return;
+        }
+
+        case Type::POINTS_COINCIDENT: {
+            EntityBase *a = SK.GetEntity(ptA);
+            EntityBase *b = SK.GetEntity(ptB);
+            if(workplane.v == EntityBase::FREE_IN_3D.v) {
+                ExprVector pa = a->PointGetExprs();
+                ExprVector pb = b->PointGetExprs();
+                AddEq(l, pa.x->Minus(pb.x), 0);
+                AddEq(l, pa.y->Minus(pb.y), 1);
+                AddEq(l, pa.z->Minus(pb.z), 2);
+            } else {
+                Expr *au, *av;
+                Expr *bu, *bv;
+                a->PointGetExprsInWorkplane(workplane, &au, &av);
+                b->PointGetExprsInWorkplane(workplane, &bu, &bv);
+                AddEq(l, au->Minus(bu), 0);
+                AddEq(l, av->Minus(bv), 1);
+            }
+            return;
+        }
+
+        case Type::PT_IN_PLANE:
+            // This one works the same, whether projected or not.
+            AddEq(l, PointPlaneDistance(
+                        SK.GetEntity(ptA)->PointGetExprs(), entityA), 0);
+            return;
+
+        case Type::PT_ON_FACE: {
+            // a plane, n dot (p - p0) = 0
+            ExprVector p = SK.GetEntity(ptA)->PointGetExprs();
+            EntityBase *f = SK.GetEntity(entityA);
+            ExprVector p0 = f->FaceGetPointExprs();
+            ExprVector n = f->FaceGetNormalExprs();
+            AddEq(l, (p.Minus(p0)).Dot(n), 0);
+            return;
+        }
+
+        case Type::PT_ON_LINE: {
+            EntityBase *ln = SK.GetEntity(entityA);
+            EntityBase *a = SK.GetEntity(ln->point[0]);
+            EntityBase *b = SK.GetEntity(ln->point[1]);
+            EntityBase *p = SK.GetEntity(ptA);
+
+            ExprVector ep = p->PointGetExprsInWorkplane(workplane);
+            ExprVector ea = a->PointGetExprsInWorkplane(workplane);
+            ExprVector eb = b->PointGetExprsInWorkplane(workplane);
+
+            ExprVector ptOnLine = ea.Plus(eb.Minus(ea).ScaledBy(Expr::From(valP)));
+            ExprVector eq = ptOnLine.Minus(ep);
+
+            AddEq(l, eq);
+            return;
+        }
+
+        case Type::PT_ON_CIRCLE: {
+            // This actually constrains the point to lie on the cylinder.
+            EntityBase *circle = SK.GetEntity(entityA);
+            ExprVector center = SK.GetEntity(circle->point[0])->PointGetExprs();
+            ExprVector pt     = SK.GetEntity(ptA)->PointGetExprs();
+            EntityBase *normal = SK.GetEntity(circle->normal);
+            ExprVector u = normal->NormalExprsU(),
+                       v = normal->NormalExprsV();
+
+            Expr *du = (center.Minus(pt)).Dot(u),
+                 *dv = (center.Minus(pt)).Dot(v);
+
+            Expr *r = circle->CircleGetRadiusExpr();
+
+            AddEq(l, du->Square()->Plus(dv->Square())->Sqrt()->Minus(r), 0);
+            return;
+        }
+
+        case Type::AT_MIDPOINT:
+            if(workplane.v == EntityBase::FREE_IN_3D.v) {
+                EntityBase *ln = SK.GetEntity(entityA);
+                ExprVector a = SK.GetEntity(ln->point[0])->PointGetExprs();
+                ExprVector b = SK.GetEntity(ln->point[1])->PointGetExprs();
+                ExprVector m = (a.Plus(b)).ScaledBy(Expr::From(0.5));
+
+                if(ptA.v) {
+                    ExprVector p = SK.GetEntity(ptA)->PointGetExprs();
+                    AddEq(l, (m.x)->Minus(p.x), 0);
+                    AddEq(l, (m.y)->Minus(p.y), 1);
+                    AddEq(l, (m.z)->Minus(p.z), 2);
+                } else {
+                    AddEq(l, PointPlaneDistance(m, entityB), 0);
+                }
+            } else {
+                EntityBase *ln = SK.GetEntity(entityA);
+                EntityBase *a = SK.GetEntity(ln->point[0]);
+                EntityBase *b = SK.GetEntity(ln->point[1]);
+
+                Expr *au, *av, *bu, *bv;
+                a->PointGetExprsInWorkplane(workplane, &au, &av);
+                b->PointGetExprsInWorkplane(workplane, &bu, &bv);
+                Expr *mu = Expr::From(0.5)->Times(au->Plus(bu));
+                Expr *mv = Expr::From(0.5)->Times(av->Plus(bv));
+
+                if(ptA.v) {
+                    EntityBase *p = SK.GetEntity(ptA);
+                    Expr *pu, *pv;
+                    p->PointGetExprsInWorkplane(workplane, &pu, &pv);
+                    AddEq(l, pu->Minus(mu), 0);
+                    AddEq(l, pv->Minus(mv), 1);
+                } else {
+                    ExprVector m = PointInThreeSpace(workplane, mu, mv);
+                    AddEq(l, PointPlaneDistance(m, entityB), 0);
+                }
+            }
+            return;
+
+        case Type::SYMMETRIC:
+            if(workplane.v == EntityBase::FREE_IN_3D.v) {
+                EntityBase *plane = SK.GetEntity(entityA);
+                EntityBase *ea = SK.GetEntity(ptA);
+                EntityBase *eb = SK.GetEntity(ptB);
+                ExprVector a = ea->PointGetExprs();
+                ExprVector b = eb->PointGetExprs();
+
+                // The midpoint of the line connecting the symmetric points
+                // lies on the plane of the symmetry.
+                ExprVector m = (a.Plus(b)).ScaledBy(Expr::From(0.5));
+                AddEq(l, PointPlaneDistance(m, plane->h), 0);
+
+                // And projected into the plane of symmetry, the points are
+                // coincident.
+                Expr *au, *av, *bu, *bv;
+                ea->PointGetExprsInWorkplane(plane->h, &au, &av);
+                eb->PointGetExprsInWorkplane(plane->h, &bu, &bv);
+                AddEq(l, au->Minus(bu), 1);
+                AddEq(l, av->Minus(bv), 2);
+            } else {
+                EntityBase *plane = SK.GetEntity(entityA);
+                EntityBase *a = SK.GetEntity(ptA);
+                EntityBase *b = SK.GetEntity(ptB);
+
+                Expr *au, *av, *bu, *bv;
+                a->PointGetExprsInWorkplane(workplane, &au, &av);
+                b->PointGetExprsInWorkplane(workplane, &bu, &bv);
+                Expr *mu = Expr::From(0.5)->Times(au->Plus(bu));
+                Expr *mv = Expr::From(0.5)->Times(av->Plus(bv));
+
+                ExprVector m = PointInThreeSpace(workplane, mu, mv);
+                AddEq(l, PointPlaneDistance(m, plane->h), 0);
+
+                // Construct a vector within the workplane that is normal
+                // to the symmetry pane's normal (i.e., that lies in the
+                // plane of symmetry). The line connecting the points is
+                // perpendicular to that constructed vector.
+                EntityBase *w = SK.GetEntity(workplane);
+                ExprVector u = w->Normal()->NormalExprsU();
+                ExprVector v = w->Normal()->NormalExprsV();
+
+                ExprVector pa = a->PointGetExprs();
+                ExprVector pb = b->PointGetExprs();
+                ExprVector n;
+                Expr *d;
+                plane->WorkplaneGetPlaneExprs(&n, &d);
+                AddEq(l, (n.Cross(u.Cross(v))).Dot(pa.Minus(pb)), 1);
+            }
+            return;
+
+        case Type::SYMMETRIC_HORIZ:
+        case Type::SYMMETRIC_VERT: {
+            ssassert(workplane.v != Entity::FREE_IN_3D.v,
+                     "Unexpected horizontal/vertical symmetric constraint in 3d");
+
+            EntityBase *a = SK.GetEntity(ptA);
+            EntityBase *b = SK.GetEntity(ptB);
+
+            Expr *au, *av, *bu, *bv;
+            a->PointGetExprsInWorkplane(workplane, &au, &av);
+            b->PointGetExprsInWorkplane(workplane, &bu, &bv);
+
+            if(type == Type::SYMMETRIC_HORIZ) {
+                AddEq(l, av->Minus(bv), 0);
+                AddEq(l, au->Plus(bu), 1);
+            } else {
+                AddEq(l, au->Minus(bu), 0);
+                AddEq(l, av->Plus(bv), 1);
+            }
+            return;
+        }
+
+        case Type::SYMMETRIC_LINE: {
+            EntityBase *pa = SK.GetEntity(ptA);
+            EntityBase *pb = SK.GetEntity(ptB);
+
+            Expr *pau, *pav, *pbu, *pbv;
+            pa->PointGetExprsInWorkplane(workplane, &pau, &pav);
+            pb->PointGetExprsInWorkplane(workplane, &pbu, &pbv);
+
+            EntityBase *ln = SK.GetEntity(entityA);
+            EntityBase *la = SK.GetEntity(ln->point[0]);
+            EntityBase *lb = SK.GetEntity(ln->point[1]);
+            Expr *lau, *lav, *lbu, *lbv;
+            la->PointGetExprsInWorkplane(workplane, &lau, &lav);
+            lb->PointGetExprsInWorkplane(workplane, &lbu, &lbv);
+
+            Expr *dpu = pbu->Minus(pau), *dpv = pbv->Minus(pav);
+            Expr *dlu = lbu->Minus(lau), *dlv = lbv->Minus(lav);
+
+            // The line through the points is perpendicular to the line
+            // of symmetry.
+            AddEq(l, (dlu->Times(dpu))->Plus(dlv->Times(dpv)), 0);
+
+            // And the signed distances of the points to the line are
+            // equal in magnitude and opposite in sign, so sum to zero
+            Expr *dista = (dlv->Times(lau->Minus(pau)))->Minus(
+                          (dlu->Times(lav->Minus(pav))));
+            Expr *distb = (dlv->Times(lau->Minus(pbu)))->Minus(
+                          (dlu->Times(lav->Minus(pbv))));
+            AddEq(l, dista->Plus(distb), 1);
+
+            return;
+        }
+
+        case Type::HORIZONTAL:
+        case Type::VERTICAL: {
+            ssassert(workplane.v != Entity::FREE_IN_3D.v,
+                     "Unexpected horizontal/vertical constraint in 3d");
+
+            hEntity ha, hb;
+            if(entityA.v) {
+                EntityBase *e = SK.GetEntity(entityA);
+                ha = e->point[0];
+                hb = e->point[1];
+            } else {
+                ha = ptA;
+                hb = ptB;
+            }
+            EntityBase *a = SK.GetEntity(ha);
+            EntityBase *b = SK.GetEntity(hb);
+
+            Expr *au, *av, *bu, *bv;
+            a->PointGetExprsInWorkplane(workplane, &au, &av);
+            b->PointGetExprsInWorkplane(workplane, &bu, &bv);
+
+            AddEq(l, (type == Type::HORIZONTAL) ? av->Minus(bv) : au->Minus(bu), 0);
+            return;
+        }
+
+        case Type::SAME_ORIENTATION: {
+            EntityBase *a = SK.GetEntity(entityA);
+            EntityBase *b = SK.GetEntity(entityB);
+
+            ExprVector au = a->NormalExprsU(),
+                       an = a->NormalExprsN();
+            ExprVector bu = b->NormalExprsU(),
+                       bv = b->NormalExprsV(),
+                       bn = b->NormalExprsN();
+
+            ExprVector eq = VectorsParallel3d(an, bn, valP);
+            AddEq(l, eq.x, 0);
+            AddEq(l, eq.y, 1);
+            AddEq(l, eq.z, 2);
+            Expr *d1 = au.Dot(bv);
+            Expr *d2 = au.Dot(bu);
+            // Allow either orientation for the coordinate system, depending
+            // on how it was drawn.
+            if(fabs(d1->Eval()) < fabs(d2->Eval())) {
+                AddEq(l, d1, 3);
+            } else {
+                AddEq(l, d2, 3);
+            }
+            return;
+        }
+
+        case Type::PERPENDICULAR:
+        case Type::ANGLE: {
+            EntityBase *a = SK.GetEntity(entityA);
+            EntityBase *b = SK.GetEntity(entityB);
+            ExprVector ae = a->VectorGetExprs();
+            ExprVector be = b->VectorGetExprs();
+            if(other) ae = ae.ScaledBy(Expr::From(-1));
+            Expr *c = DirectionCosine(workplane, ae, be);
+
+            if(type == Type::ANGLE) {
+                // The direction cosine is equal to the cosine of the
+                // specified angle
+                Expr *rads = exA->Times(Expr::From(PI/180)),
+                     *rc   = rads->Cos();
+                double arc = fabs(rc->Eval());
+                // avoid false detection of inconsistent systems by gaining
+                // up as the difference in dot products gets small at small
+                // angles; doubles still have plenty of precision, only
+                // problem is that rank test
+                Expr *mult = Expr::From(arc > 0.99 ? 0.01/(1.00001 - arc) : 1);
+                AddEq(l, (c->Minus(rc))->Times(mult), 0);
+            } else {
+                // The dot product (and therefore the direction cosine)
+                // is equal to zero, perpendicular.
+                AddEq(l, c, 0);
+            }
+            return;
+        }
+
+        case Type::EQUAL_ANGLE: {
+            EntityBase *a = SK.GetEntity(entityA);
+            EntityBase *b = SK.GetEntity(entityB);
+            EntityBase *c = SK.GetEntity(entityC);
+            EntityBase *d = SK.GetEntity(entityD);
+            ExprVector ae = a->VectorGetExprs();
+            ExprVector be = b->VectorGetExprs();
+            ExprVector ce = c->VectorGetExprs();
+            ExprVector de = d->VectorGetExprs();
+
+            if(other) ae = ae.ScaledBy(Expr::From(-1));
+
+            Expr *cab = DirectionCosine(workplane, ae, be);
+            Expr *ccd = DirectionCosine(workplane, ce, de);
+
+            AddEq(l, cab->Minus(ccd), 0);
+            return;
+        }
+
+        case Type::ARC_LINE_TANGENT: {
+            EntityBase *arc  = SK.GetEntity(entityA);
+            EntityBase *line = SK.GetEntity(entityB);
+
+            ExprVector ac = SK.GetEntity(arc->point[0])->PointGetExprs();
+            ExprVector ap =
+                SK.GetEntity(arc->point[other ? 2 : 1])->PointGetExprs();
+
+            ExprVector ld = line->VectorGetExprs();
+
+            // The line is perpendicular to the radius
+            AddEq(l, ld.Dot(ac.Minus(ap)), 0);
+            return;
+        }
+
+        case Type::CUBIC_LINE_TANGENT: {
+            EntityBase *cubic = SK.GetEntity(entityA);
+            EntityBase *line  = SK.GetEntity(entityB);
+
+            ExprVector a;
+            if(other) {
+                a = cubic->CubicGetFinishTangentExprs();
+            } else {
+                a = cubic->CubicGetStartTangentExprs();
+            }
+
+            ExprVector b = line->VectorGetExprs();
+
+            if(workplane.v == EntityBase::FREE_IN_3D.v) {
+                ExprVector eq = VectorsParallel3d(a, b, valP);
+                AddEq(l, eq);
+            } else {
+                EntityBase *w = SK.GetEntity(workplane);
+                ExprVector wn = w->Normal()->NormalExprsN();
+                AddEq(l, (a.Cross(b)).Dot(wn), 0);
+            }
+            return;
+        }
+
+        case Type::CURVE_CURVE_TANGENT: {
+            bool parallel = true;
+            int i;
+            ExprVector dir[2];
+            for(i = 0; i < 2; i++) {
+                EntityBase *e = SK.GetEntity((i == 0) ? entityA : entityB);
+                bool oth = (i == 0) ? other : other2;
+
+                if(e->type == Entity::Type::ARC_OF_CIRCLE) {
+                    ExprVector center, endpoint;
+                    center = SK.GetEntity(e->point[0])->PointGetExprs();
+                    endpoint =
+                        SK.GetEntity(e->point[oth ? 2 : 1])->PointGetExprs();
+                    dir[i] = endpoint.Minus(center);
+                    // We're using the vector from the center of the arc to
+                    // an endpoint; so that's normal to the tangent, not
+                    // parallel.
+                    parallel = !parallel;
+                } else if(e->type == Entity::Type::CUBIC) { // BRANCH_ALWAYS_TAKEN
+                    if(oth) {
+                        dir[i] = e->CubicGetFinishTangentExprs();
+                    } else {
+                        dir[i] = e->CubicGetStartTangentExprs();
+                    }
+                } else {
+                    ssassert(false, "Unexpected entity types for CURVE_CURVE_TANGENT");
+                }
+            }
+            if(parallel) {
+                EntityBase *w = SK.GetEntity(workplane);
+                ExprVector wn = w->Normal()->NormalExprsN();
+                AddEq(l, ((dir[0]).Cross(dir[1])).Dot(wn), 0);
+            } else {
+                AddEq(l, (dir[0]).Dot(dir[1]), 0);
+            }
+            return;
+        }
+
+        case Type::PARALLEL: {
+            EntityBase *ea = SK.GetEntity(entityA), *eb = SK.GetEntity(entityB);
+            ExprVector a = ea->VectorGetExprsInWorkplane(workplane);
+            ExprVector b = eb->VectorGetExprsInWorkplane(workplane);
+
+            if(workplane.v == EntityBase::FREE_IN_3D.v) {
+                ExprVector eq = VectorsParallel3d(a, b, valP);
+                AddEq(l, eq);
+            } else {
+                // We use expressions written in workplane csys, so we can assume the workplane
+                // normal is (0, 0, 1). We can write the equation as:
+                //   Expr *eq = a.Cross(b).Dot(ExprVector::From(0.0, 0.0, 1.0));
+                // but this will just result in elimination of x and y terms after dot product.
+                // We can only use the z expression:
+                //   Expr *eq = a.Cross(b).z;
+                // but it's more efficient to write it in the terms of pseudo-scalar product:
+                Expr *eq = (a.x->Times(b.y))->Minus(a.y->Times(b.x));
+                AddEq(l, eq, 0);
+            }
+
+            return;
+        }
+
+        case Type::WHERE_DRAGGED: {
+            EntityBase *ep = SK.GetEntity(ptA);
+            if(workplane.v == EntityBase::FREE_IN_3D.v) {
+                ExprVector ev = ep->PointGetExprs();
+                Vector v = ep->PointGetNum();
+
+                AddEq(l, ev.x->Minus(Expr::From(v.x)), 0);
+                AddEq(l, ev.y->Minus(Expr::From(v.y)), 1);
+                AddEq(l, ev.z->Minus(Expr::From(v.z)), 2);
+            } else {
+                Expr *u, *v;
+                ep->PointGetExprsInWorkplane(workplane, &u, &v);
+                AddEq(l, u->Minus(Expr::From(u->Eval())), 0);
+                AddEq(l, v->Minus(Expr::From(v->Eval())), 1);
+            }
+            return;
+        }
+
+        case Type::COMMENT:
+            return;
+    }
+    ssassert(false, "Unexpected constraint ID");
+}
+
--- a/Show More
+++ b/Show More
				`@@ -0,0 +1 @@`
				`<svg xmlns="http://www.w3.org/2000/svg" width="24" height="24" viewBox="0 0 24 24" fill="none" stroke="#b6b6b6" stroke-width="0.85" stroke-linecap="round" stroke-linejoin="round"><path d="M4 17 A11 11 0 0 1 20 17"/><circle cx="4" cy="17" r="1.5" fill="#b6b6b6" stroke="none"/><circle cx="12" cy="7" r="1.5" fill="#b6b6b6" stroke="none"/><circle cx="20" cy="17" r="1.5" fill="#b6b6b6" stroke="none"/></svg>`
				`@@ -0,0 +1 @@`
				<svg xmlns="http://www.w3.org/2000/svg" width="24" height="24" viewBox="0 0 24 24" fill="none" stroke="#b6b6b6" stroke-width="0.85" stroke-linecap="round" stroke-linejoin="round"><circle cx="12" cy="12" r="8" stroke-dasharray="2.5 2.5" opacity="0.5"/><circle cx="12" cy="12" r="1.4" fill="#b6b6b6" stroke="none"/><circle cx="12" cy="4" r="1.8" fill="#b6b6b6" stroke="none"/><circle cx="18.9" cy="8" r="1.8" fill="#b6b6b6" stroke="none"/><circle cx="18.9" cy="16" r="1.8" fill="#b6b6b6" stroke="none"/><circle cx="12" cy="20" r="1.8" fill="#b6b6b6" stroke="none"/><circle cx="5.1" cy="16" r="1.8" fill="#b6b6b6" stroke="none"/><circle cx="5.1" cy="8" r="1.8" fill="#b6b6b6" stroke="none"/></svg>