docs/design_tab_upstream_portability.md explains the subsystem to a
maintainer; nothing explained it to a user. This is that: what the tab is,
how to get a first solid out of it, every tool grouped the way the toolbar
groups them, and the keyboard shortcuts read out of the source rather than
remembered.
The limitations section is deliberate. Rib needing a sketch with an explicit
open line, Surface Loft and Surface Fill having no hands-on verification, mates
composing transforms instead of solving simultaneously, move-face and
replace-face being absent, and the two quarantined kernel tests are all things
a user would otherwise discover by hitting them.
Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>
Maintainers will ask what the Design tab costs before they will look at the
diff, so measure it rather than assert it.
The headline correction: the OCCT delta is THREE toolkits, not two. The
comment in deps/OCCT/OCCT.cmake claimed "TKFillet + TKOffset (3.77 MiB,
Windows only)". Walking OCCT's own adm/MODULES and each toolkit's EXTERNLIB
shows ModelingAlgorithms holds twelve toolkits, that eight of them are built
either way because DataExchange (the STEP path upstream already ships) depends
on them, and that the true delta is TKFeat, TKFillet, TKOffset and TKXMesh —
of which TKXMesh is never produced. So three archives are built: 7.40, 5.38
and 4.42 MiB.
TKFeat is the interesting one. Nothing in the Design tab references it and it
is absent from the TKFillet/TKOffset dependency closure, so it is built for
nothing — OCCT's module flag is all-or-nothing per module. On static-link
platforms that is build time and zero shipped bytes.
Two numbers are deliberately absent, marked as absent, and not approximated:
the Windows DLL delta needs a Windows build (snaporca-gix), and a clean-build
time delta needs the deps prefix built twice on one machine. The old 3.77 MiB
figure is withdrawn rather than reused — it covered two of the three toolkits.
Also recorded: the vendored solver is 9,339 lines under GPLv3 with its LICENSE
preserved, which combines into this AGPLv3 fork without difficulty (AGPLv3
§13), and it is live code driving every sketch constraint — not a carried
corpse.
Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>
Enumerated from the source rather than from recollection: CadFeatureType and
add_* in CadDocument.hpp, Tool in DesignPanel.hpp, Mode in
DesignSketchTool.hpp, SketchConstraintType + SketchEntity::Type in
SketchEngine.hpp, and the JSON-RPC dispatch in McpControl.cpp.
Findings worth stating up front:
- The 2D sketcher is at or near Onshape parity -- 19 constraints, every entity
type including B-splines and elliptical arcs, trim/extend/offset/mirror and
both array kinds. Very little is missing there.
- The gaps are all breadth beyond sketching: assemblies/mates, surface
modelling, sheet metal, drawings, and variables/configurations.
- The most defensible criticism is the absence of variables and expressions.
Every dimension is a literal double, so the feature tree is parametric in
structure but not in value -- "change one number and the model updates" is
only half delivered. It is also the cheapest Tier 1 item to close.
The doc separates platform capabilities (version control, FeatureScript, FEA,
rendering, cloud PDM) into their own tier rather than counting them as missing
tools: that is Onshape-the-platform, not Onshape-the-modeller, and holding a
slicer tab to it would not be a fair comparison.
One entry is a correctness gap rather than a missing feature: move/rotate body
(m_body_xform) is display-only and never enters the B-rep, so a moved body
exports and booleans at its original position while the viewport shows it
moved.
Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01BVzKmX6Y1aEteit1HTXG4Q
The 2026-06-21 assessment was written before the persistence work landed and
got two load-bearing facts wrong. Both are corrected here against the branch
itself rather than from recollection:
1. It called OCCT "a dependency mainline OrcaSlicer has never carried" and
built its whole conclusion on that. False: deps/OCCT/ exists at the
merge-base, and upstream already links it from Format/STEP.cpp,
Format/svg.cpp and Shape/TextShape.cpp. The real dependency diff is one
line -- BUILD_MODULE_ModelingAlgorithms OFF -> ON -- costing a measured
3.77 MiB of Windows DLLs (TKFillet + TKOffset; TKBool already arrives
transitively via DataExchange).
2. It described the vendored SolveSpace solver as LGPL. False:
src/libslic3r/slvs/LICENSE is GPL-3.0. Harmless for us, but a licence
must not be misstated in a document aimed at upstream.
It also claimed no changes to Model, which stopped being true when 3MF
recipe persistence added a std::string there.
The rewrite replaces prose estimates with counted figures: 138 new files,
23 modified upstream files at +457/-75, nothing deleted, 99.3 % of the diff
in new files. That reframes the ask from "adopt a CAD kernel" to "widen a
build flag you already carry", which is the argument that actually has a
chance upstream.
Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01BVzKmX6Y1aEteit1HTXG4Q
