M7c: SurfaceLoft + SurfaceFill (open skins from profiles / a boundary)

The two remaining ways to create a sheet body. SurfaceLoft skins 2+ profile
sketches without end caps via a new SketchEngine::make_loft_surface — a
sibling of make_loft with the ThruSections solid flag false, so no existing
call site changes. SurfaceFill patches a single closed boundary wire into a
smooth face with BRepOffsetAPI_MakeFilling, adding each boundary edge as a
C0 constraint.

Purely additive: two enum values appended to CadFeatureType, reusing the
existing loft_profile_refs/loft_ruled and sketch_ref fields. No new cereal
fields, recipe stays v2, golden fixture unchanged (30773). MCP
surface_loft/surface_fill added as pure additions. Suite 107 cases / 1553
assertions green, including a test contrasting the open skin against the
solid loft of the same profiles.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01BVzKmX6Y1aEteit1HTXG4Q

src/libslic3r/CadDocument.cpp

@@ -19,6 +19,7 @@
 #include <BRepOffsetAPI_MakePipeShell.hxx>
 #include <BRepOffsetAPI_MakeThickSolid.hxx>
 #include <BRepOffsetAPI_MakeOffsetShape.hxx>
+#include <BRepOffsetAPI_MakeFilling.hxx>
 #include <BRepOffsetAPI_DraftAngle.hxx>
 #include <Bnd_Box.hxx>
 #include <BRepBndLib.hxx>
@@ -36,6 +37,7 @@
 #include <Geom_CylindricalSurface.hxx>
 #include <Geom_ConicalSurface.hxx>
 #include <Geom2d_TrimmedCurve.hxx>
+#include <GeomAbs_Shape.hxx>        // SurfaceFill: GeomAbs_C0
 #include <GCE2d_MakeSegment.hxx>
 #include <TopoDS_Edge.hxx>
 #include <TopoDS_Face.hxx>
@@ -44,6 +46,7 @@
 #include <TopoDS_Compound.hxx>      // multi-body: compound of bodies for display/compat
 #include <BRep_Builder.hxx>
 #include <TopAbs_Orientation.hxx>   // outward-normal orientation for face-extrude
+#include <TopoDS.hxx>               // TopoDS::Edge for SurfaceFill
 #include <TopExp_Explorer.hxx>      // is_sheet_shape
 #include <gp_Circ.hxx>
 #include <gp_Ax2.hxx>
@@ -2076,6 +2079,44 @@ void CadDocument::apply_feature(TopoDS_Shape& result, bool& have_body,
         result = rev.Shape(); have_body = true;
         break;
     }
+    case CadFeatureType::SurfaceLoft: {
+        std::vector<TopoDS_Wire> profiles;
+        for (int ref : f.loft_profile_refs) {
+            if (ref < 0 || ref >= int(features.size())
+                || (features[ref].type != CadFeatureType::Sketch
+                    && features[ref].type != CadFeatureType::Project))
+                continue;
+            profiles.push_back(build_sketch_wire(features[ref]));
+        }
+        if (profiles.size() < 2)
+            throw std::runtime_error("surface-loft needs 2+ valid profile sketches");
+        TopoDS_Shape skin = SketchEngine::make_loft_surface(profiles, f.loft_ruled);
+        if (skin.IsNull()) throw std::runtime_error("surface-loft: loft failed");
+        result = skin; have_body = true;
+        break;
+    }
+    case CadFeatureType::SurfaceFill: {
+        if (f.sketch_ref < 0 || f.sketch_ref >= int(features.size()))
+            throw std::runtime_error("surface-fill: bad sketch ref");
+        const CadFeature& sk = features[f.sketch_ref];
+        if (sk.type != CadFeatureType::Sketch && sk.type != CadFeatureType::Project)
+            throw std::runtime_error("surface-fill: ref is not a sketch");
+        TopoDS_Wire wire = build_sketch_wire(sk);
+        if (wire.IsNull()) throw std::runtime_error("surface-fill: empty boundary");
+        BRepOffsetAPI_MakeFilling fill;
+        int nedges = 0;
+        for (TopExp_Explorer ex(wire, TopAbs_EDGE); ex.More(); ex.Next()) {
+            fill.Add(TopoDS::Edge(ex.Current()), GeomAbs_C0);
+            ++nedges;
+        }
+        if (nedges == 0) throw std::runtime_error("surface-fill: boundary has no edges");
+        fill.Build();
+        if (!fill.IsDone()) throw std::runtime_error("surface-fill: fill failed");
+        TopoDS_Shape face = fill.Shape();
+        if (face.IsNull()) throw std::runtime_error("surface-fill: produced no geometry");
+        result = face; have_body = true;
+        break;
+    }
     case CadFeatureType::Sweep: {
         const CadFeature& sk = (f.sketch_ref >= 0 && f.sketch_ref < int(features.size())
                                 && (features[f.sketch_ref].type == CadFeatureType::Sketch
@@ -2855,6 +2896,7 @@ void CadDocument::route_feature(std::vector<CadBody>& bodies, const CadFeature&
         || f.type == CadFeatureType::Import   // an imported solid is always its own base body
         || f.type == CadFeatureType::SurfaceExtrude || f.type == CadFeatureType::SurfaceRevolve
         || f.type == CadFeatureType::ThickenSurface || f.type == CadFeatureType::SurfaceOffset
+        || f.type == CadFeatureType::SurfaceLoft || f.type == CadFeatureType::SurfaceFill
         || ((f.type == CadFeatureType::Extrude || f.type == CadFeatureType::Revolve
              || f.type == CadFeatureType::Sweep || f.type == CadFeatureType::Loft)
             && f.mode == BooleanMode::New);
@@ -3112,6 +3154,29 @@ int CadDocument::add_surface_revolve(int sketch_ref, double angle_deg, int axis,
     return int(features.size()) - 1;
 }
 
+int CadDocument::add_surface_loft(const std::vector<int>& profile_refs, bool ruled, const std::string& name)
+{
+    CadFeature f;
+    f.type              = CadFeatureType::SurfaceLoft;
+    f.name              = name;
+    f.loft_profile_refs = profile_refs;
+    f.loft_ruled        = ruled;
+    f.mode              = BooleanMode::New;
+    features.push_back(f);
+    return int(features.size()) - 1;
+}
+
+int CadDocument::add_surface_fill(int sketch_ref, const std::string& name)
+{
+    CadFeature f;
+    f.type       = CadFeatureType::SurfaceFill;
+    f.name       = name;
+    f.sketch_ref = sketch_ref;
+    f.mode       = BooleanMode::New;
+    features.push_back(f);
+    return int(features.size()) - 1;
+}
+
 // ponytail: derived from the OCCT shape type; no stored flag, bodies aren't serialized anyway.
 bool CadDocument::is_sheet_shape(const TopoDS_Shape& s)
 {

src/libslic3r/CadDocument.hpp

@@ -19,7 +19,7 @@
 
 namespace Slic3r {
 
-enum class CadFeatureType { Sketch, Extrude, Fillet, Chamfer, Hole, Thread, Shell, Revolve, Sweep, Pattern, Plane, Loft, Draft, Import, Boolean, Cut, Mirror, Axis, CoordSys, Helix, Transform, Thicken, Project, DeleteFace, Rib, SurfaceExtrude, SurfaceRevolve, ThickenSurface, SurfaceOffset };
+enum class CadFeatureType { Sketch, Extrude, Fillet, Chamfer, Hole, Thread, Shell, Revolve, Sweep, Pattern, Plane, Loft, Draft, Import, Boolean, Cut, Mirror, Axis, CoordSys, Helix, Transform, Thicken, Project, DeleteFace, Rib, SurfaceExtrude, SurfaceRevolve, ThickenSurface, SurfaceOffset, SurfaceLoft, SurfaceFill };
 enum class SketchShape    { Rectangle, Circle };
 enum class PlaneType      { Offset, Angle, Midplane, Tangent, TwoEdges, Coincident };
 enum class AxisType       { TwoPoints, FaceNormal, CylinderCenterline, PlaneIntersection, AlongEdge };
@@ -479,6 +479,10 @@ public:
     // 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);
+    // Skin 2+ profile sketches open (no end caps) -> a sheet body.
+    int  add_surface_loft(const std::vector<int>& profile_refs, bool ruled, const std::string& name);
+    // Fill sketch sketch_ref's closed boundary wire with a smooth face -> a one-face sheet body.
+    int  add_surface_fill(int sketch_ref, const std::string& name);
     int  add_shell(double thickness, int face, int target_body, const std::string& name);
     // Grow a thin rib wall (thickness, depth) from the open Line entity `entity` inside sketch
     // feature `sketch_ref`, fused to `target_body`. Returns the new feature index.

src/libslic3r/SketchEngine.cpp

@@ -378,6 +378,24 @@ TopoDS_Shape SketchEngine::make_loft(const std::vector<TopoDS_Wire>& profiles, b
     return s;
 }
 
+// ponytail: sibling of make_loft that builds an open shell (sheet) instead of a solid.
+TopoDS_Shape SketchEngine::make_loft_surface(const std::vector<TopoDS_Wire>& profiles, bool ruled)
+{
+    if (profiles.size() < 2)
+        throw std::runtime_error("loft needs at least 2 profiles");
+    BRepOffsetAPI_ThruSections loft(Standard_False /*shell, no end caps*/,
+                                    ruled ? Standard_True : Standard_False);
+    for (const TopoDS_Wire& w : profiles) {
+        if (w.IsNull()) throw std::runtime_error("loft: null profile wire");
+        loft.AddWire(w);
+    }
+    loft.Build();
+    if (!loft.IsDone()) throw std::runtime_error("loft failed");
+    TopoDS_Shape s = loft.Shape();
+    if (s.IsNull()) throw std::runtime_error("loft produced no shape");
+    return s;
+}
+
 TopoDS_Shape SketchEngine::make_pocket(const TopoDS_Wire& wire, const SketchPlane& plane,
                                         const TopoDS_Shape& target, double depth)
 {

src/libslic3r/SketchEngine.hpp

@@ -192,6 +192,11 @@ public:
     // given order. ruled=true => straight (ruled) sections; false => smooth (C2).
     static TopoDS_Shape make_loft(const std::vector<TopoDS_Wire>& profiles, bool ruled);
 
+    // Skin `profiles` WITHOUT end caps -> an open shell (sheet). Same as make_loft but the
+    // ThruSections solid flag is false. // ponytail: a sibling instead of a bool param, so no
+    // existing call site changes.
+    static TopoDS_Shape make_loft_surface(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);
 

src/slic3r/GUI/McpControl.cpp

@@ -1070,6 +1070,35 @@ json action_surface_offset(DesignPanel* panel, const json& params)
     return json{{"ok", ok}, {"feature_index", idx}, {"bodies", int(doc.bodies.size())}, {"error", doc.error}};
 }
 
+json action_surface_loft(DesignPanel* panel, const json& params)
+{
+    if (!params.contains("profiles") || !params["profiles"].is_array())
+        throw std::runtime_error("surface_loft needs 'profiles' (array of int feature indices)");
+    CadDocument& doc = panel->mcp_doc();
+    std::vector<int> profiles;
+    for (const json& j : params["profiles"]) profiles.push_back(j.get<int>());
+    bool ruled = params.value("ruled", false);
+    doc.checkpoint();
+    int idx = doc.add_surface_loft(profiles, ruled, "SurfaceLoft");
+    bool ok = doc.recompute();
+    if (!ok) doc.undo();
+    panel->mcp_after_change();
+    return json{{"ok", ok}, {"feature_index", idx}, {"bodies", int(doc.bodies.size())}, {"error", doc.error}};
+}
+
+json action_surface_fill(DesignPanel* panel, const json& params)
+{
+    if (!params.contains("sketch")) throw std::runtime_error("surface_fill needs 'sketch' (feature index)");
+    CadDocument& doc = panel->mcp_doc();
+    int sketch = params["sketch"].get<int>();
+    doc.checkpoint();
+    int idx = doc.add_surface_fill(sketch, "SurfaceFill");
+    bool ok = doc.recompute();
+    if (!ok) doc.undo();
+    panel->mcp_after_change();
+    return json{{"ok", ok}, {"feature_index", idx}, {"bodies", int(doc.bodies.size())}, {"error", doc.error}};
+}
+
 json action_draft(DesignPanel* panel, const json& params)
 {
     if (!params.contains("face")) throw std::runtime_error("draft needs 'face' (id from query_topology)");
@@ -1363,6 +1392,8 @@ std::string handle_on_main(const std::string& method, const json& params, const
         if (method == "surface_revolve")  return rpc_result(id, action_surface_revolve(panel, params));
         if (method == "thicken_surface")  return rpc_result(id, action_thicken_surface(panel, params));
         if (method == "surface_offset")   return rpc_result(id, action_surface_offset(panel, params));
+        if (method == "surface_loft")    return rpc_result(id, action_surface_loft(panel, params));
+        if (method == "surface_fill")    return rpc_result(id, action_surface_fill(panel, params));
         return rpc_error(id, -32601, "Unknown method: " + method);
     } catch (const Standard_Failure& ex) {   // OCCT errors are NOT std::exception
         return rpc_error(id, -32000, std::string("OCCT: ") + (ex.GetMessageString() ? ex.GetMessageString() : "failure"));

tests/libslic3r/test_caddocument.cpp

@@ -4752,3 +4752,125 @@ TEST_CASE("thicken-surface round-trip serialize/deserialize", "[CadDocument][sur
     REQUIRE_THAT(double(fy1), WithinAbs(double(oy1), 1e-6));
     REQUIRE_THAT(double(fz1), WithinAbs(double(oz1), 1e-6));
 }
+
+TEST_CASE("surface-loft makes an open shell", "[CadDocument][surface]")
+{
+    using Catch::Matchers::WithinAbs;
+
+    CadDocument doc;
+    SketchProfile bot;
+    bot.points = {{-10,-10},{10,-10},{10,10},{-10,10}};
+    bot.closed = true;
+    int s0 = doc.add_sketch_profile(bot, SketchPlane::XY(), "Bottom");
+
+    doc.add_plane(0 /*XY*/, 20.0, 0.0, 0, "Plane1");
+    SketchPlane top = doc.resolve_datum_planes()[0].second;
+    SketchProfile tp;
+    tp.points = {{-5,-5},{5,-5},{5,5},{-5,5}};
+    tp.closed = true;
+    int s1 = doc.add_sketch_profile(tp, top, "Top");
+
+    int fi = doc.add_surface_loft({s0, s1}, false, "Skin");
+    REQUIRE(fi >= 0);
+    REQUIRE(doc.recompute());
+    REQUIRE(doc.error.empty());
+    REQUIRE(doc.bodies.size() == 1);
+    REQUIRE(CadDocument::is_sheet_shape(doc.bodies.back().shape));
+
+    // Contrast with a solid loft on the same profiles.
+    CadDocument doc2;
+    SketchProfile bot2;
+    bot2.points = {{-10,-10},{10,-10},{10,10},{-10,10}};
+    bot2.closed = true;
+    int a0 = doc2.add_sketch_profile(bot2, SketchPlane::XY(), "Bottom");
+    doc2.add_plane(0 /*XY*/, 20.0, 0.0, 0, "Plane1");
+    SketchPlane top2 = doc2.resolve_datum_planes()[0].second;
+    SketchProfile tp2;
+    tp2.points = {{-5,-5},{5,-5},{5,5},{-5,5}};
+    tp2.closed = true;
+    int a1 = doc2.add_sketch_profile(tp2, top2, "Top");
+    doc2.add_loft({a0, a1}, false, BooleanMode::New, "SolidLoft");
+    REQUIRE(doc2.recompute());
+    REQUIRE(doc2.error.empty());
+    REQUIRE_FALSE(CadDocument::is_sheet_shape(doc2.bodies.back().shape));
+}
+
+TEST_CASE("surface-fill makes a one-face sheet", "[CadDocument][surface]")
+{
+    CadDocument doc;
+    int sk = doc.add_sketch(SketchShape::Rectangle, SketchPlane::XY(), 20, 20, 0, "Rect");
+    REQUIRE(sk >= 0);
+    int fi = doc.add_surface_fill(sk, "Patch");
+    REQUIRE(fi == 1);
+    REQUIRE(doc.recompute());
+    REQUIRE(doc.error.empty());
+    REQUIRE(doc.bodies.size() == 1);
+    REQUIRE(CadDocument::is_sheet_shape(doc.bodies.back().shape));
+
+    int face_count = 0;
+    for (TopExp_Explorer fe(doc.bodies.back().shape, TopAbs_FACE); fe.More(); fe.Next()) ++face_count;
+    REQUIRE(face_count >= 1);
+}
+
+TEST_CASE("surface-loft / surface-fill bad refs safe", "[CadDocument][surface]")
+{
+    {
+        CadDocument doc;
+        doc.add_surface_loft({999}, false, "Bad");
+        REQUIRE_FALSE(doc.recompute());
+        REQUIRE_THAT(doc.error, Catch::Matchers::Contains("surface-loft"));
+    }
+    {
+        CadDocument doc;
+        doc.add_surface_fill(999, "Bad");
+        REQUIRE_FALSE(doc.recompute());
+        REQUIRE_THAT(doc.error, Catch::Matchers::Contains("surface-fill"));
+    }
+}
+
+TEST_CASE("surface-loft round-trip serialize/deserialize", "[CadDocument][surface]")
+{
+    using Catch::Matchers::WithinAbs;
+
+    CadDocument doc;
+    SketchProfile bot;
+    bot.points = {{-10,-10},{10,-10},{10,10},{-10,10}};
+    bot.closed = true;
+    int s0 = doc.add_sketch_profile(bot, SketchPlane::XY(), "Bottom");
+    doc.add_plane(0 /*XY*/, 20.0, 0.0, 0, "Plane1");
+    SketchPlane top = doc.resolve_datum_planes()[0].second;
+    SketchProfile tp;
+    tp.points = {{-5,-5},{5,-5},{5,5},{-5,5}};
+    tp.closed = true;
+    int s1 = doc.add_sketch_profile(tp, top, "Top");
+    doc.add_surface_loft({s0, s1}, false, "Skin");
+    REQUIRE(doc.recompute());
+    REQUIRE(doc.error.empty());
+    REQUIRE(CadDocument::is_sheet_shape(doc.bodies.back().shape));
+
+    size_t orig_nb = doc.bodies.size();
+    Bnd_Box orig_bb;
+    BRepBndLib::Add(doc.bodies.back().shape, orig_bb);
+
+    std::string blob = doc.serialize_recipe();
+    REQUIRE_FALSE(blob.empty());
+
+    CadDocument fresh;
+    REQUIRE(fresh.deserialize_recipe(blob));
+    REQUIRE(fresh.error.empty());
+    REQUIRE(fresh.bodies.size() == orig_nb);
+    REQUIRE(CadDocument::is_sheet_shape(fresh.bodies.back().shape));
+
+    Bnd_Box fresh_bb;
+    BRepBndLib::Add(fresh.bodies.back().shape, fresh_bb);
+    Standard_Real ox0, oy0, oz0, ox1, oy1, oz1;
+    Standard_Real fx0, fy0, fz0, fx1, fy1, fz1;
+    orig_bb.Get(ox0, oy0, oz0, ox1, oy1, oz1);
+    fresh_bb.Get(fx0, fy0, fz0, fx1, fy1, fz1);
+    REQUIRE_THAT(double(fx0), WithinAbs(double(ox0), 1e-6));
+    REQUIRE_THAT(double(fy0), WithinAbs(double(oy0), 1e-6));
+    REQUIRE_THAT(double(fz0), WithinAbs(double(oz0), 1e-6));
+    REQUIRE_THAT(double(fx1), WithinAbs(double(ox1), 1e-6));
+    REQUIRE_THAT(double(fy1), WithinAbs(double(oy1), 1e-6));
+    REQUIRE_THAT(double(fz1), WithinAbs(double(oz1), 1e-6));
+}