From 8790b07773a126c17b8dd115baae07ee1985d6f5 Mon Sep 17 00:00:00 2001
From: Kris Austin <kris.austin@gmail.com>
Date: Thu, 8 Oct 2026 16:10:37 -0500
Subject: [PATCH] fix: missing chamfers on STEP import since the OCCT 8.0.1
 update (#16290)

---
 ...epMesh-seam-pcurve-at-edge-parameter.patch |  28 +++
 deps/OCCT/OCCT.cmake                          |   7 +
 tests/data/cone_tilted_seam_pcurve.step       | 166 ++++++++++++++++++
 tests/libslic3r/test_step.cpp                 |  18 ++
 4 files changed, 219 insertions(+)
 create mode 100644 deps/OCCT/0001-BRepMesh-seam-pcurve-at-edge-parameter.patch
 create mode 100644 tests/data/cone_tilted_seam_pcurve.step

diff --git a/deps/OCCT/0001-BRepMesh-seam-pcurve-at-edge-parameter.patch b/deps/OCCT/0001-BRepMesh-seam-pcurve-at-edge-parameter.patch
new file mode 100644
index 0000000000..84c599a5f3
--- /dev/null
+++ b/deps/OCCT/0001-BRepMesh-seam-pcurve-at-edge-parameter.patch
@@ -0,0 +1,28 @@
+diff --git a/src/ModelingAlgorithms/TKMesh/BRepMesh/BRepMesh_ModelPreProcessor.cxx b/src/ModelingAlgorithms/TKMesh/BRepMesh/BRepMesh_ModelPreProcessor.cxx
+index 6f63781..9b1c08e 100644
+--- a/src/ModelingAlgorithms/TKMesh/BRepMesh/BRepMesh_ModelPreProcessor.cxx
++++ b/src/ModelingAlgorithms/TKMesh/BRepMesh/BRepMesh_ModelPreProcessor.cxx
+@@ -210,10 +210,10 @@ private:
+ 
+     // Define two pcurves of the seam-edge.
+     occ::handle<Geom2d_Curve> aPC1, aPC2;
+-    double                    af, al;
++    double                    af, al, af1, al1;
+ 
+     aE.Orientation(TopAbs_FORWARD);
+-    aPC1 = BRep_Tool::CurveOnSurface(aE, aF, af, al);
++    aPC1 = BRep_Tool::CurveOnSurface(aE, aF, af1, al1);
+ 
+     aE.Orientation(TopAbs_REVERSED);
+     aPC2 = BRep_Tool::CurveOnSurface(aE, aF, af, al);
+@@ -224,7 +224,9 @@ private:
+     }
+ 
+     // Select the correct pcurve of the seam-edge.
+-    const gp_Pnt2d& aFPntOfPC1 = aPC1->Value(aPC1->FirstParameter());
++    // Use the edge's first parameter. A Geom2d_Line's FirstParameter() is -Precision::Infinite(),
++    // where a direction of (2e-16, -1) from rounding error gives an X far outside the U range.
++    const gp_Pnt2d aFPntOfPC1 = aPC1->Value(af1);
+ 
+     if (std::abs(aLPntOfIPC1.X() - aFPntOfPC1.X()) > Precision::Confusion())
+     {
diff --git a/deps/OCCT/OCCT.cmake b/deps/OCCT/OCCT.cmake
index 4cab60ec6a..0466d8e868 100644
--- a/deps/OCCT/OCCT.cmake
+++ b/deps/OCCT/OCCT.cmake
@@ -25,9 +25,16 @@ endif()
 # shipped bytes. Windows ships only the DLLs libslic3r links, so the tab adds the TKFillet,
 # TKOffset and TKBool DLLs. See docs/HLSD/design-tab.md.
 
+if (IN_GIT_REPO)
+    set(OCCT_DIRECTORY_FLAG --directory ${BINARY_DIR_REL}/dep_OCCT-prefix/src/dep_OCCT)
+endif ()
+
 orcaslicer_add_cmake_project(OCCT
     URL https://github.com/Open-Cascade-SAS/OCCT/archive/refs/tags/V8_0_1.zip
     URL_HASH SHA256=7c033d917ee8f040c0512d289dcc5f02c148889d5bac17c3e25639accb44f0da
+    # Makes BRepMesh triangulate cone faces whose seam pcurve is slightly tilted
+    # (Open-Cascade-SAS/OCCT#572); remove the patch once an OCCT release includes the fix.
+    PATCH_COMMAND git apply ${OCCT_DIRECTORY_FLAG} --verbose --ignore-space-change --whitespace=fix ${CMAKE_CURRENT_LIST_DIR}/0001-BRepMesh-seam-pcurve-at-edge-parameter.patch
     #DEPENDS dep_Boost
     DEPENDS ${FREETYPE_PKG}
     CMAKE_ARGS
diff --git a/tests/data/cone_tilted_seam_pcurve.step b/tests/data/cone_tilted_seam_pcurve.step
new file mode 100644
index 0000000000..172012114b
--- /dev/null
+++ b/tests/data/cone_tilted_seam_pcurve.step
@@ -0,0 +1,166 @@
+ISO-10303-21;
+HEADER;
+FILE_DESCRIPTION(('Open CASCADE Model'),'2;1');
+FILE_NAME('Open CASCADE Shape Model','2026-10-08T09:57:33',('Author'),(
+    'Open CASCADE'),'Open CASCADE STEP processor 8.0','Open CASCADE 8.0'
+  ,'Unknown');
+FILE_SCHEMA(('AUTOMOTIVE_DESIGN { 1 0 10303 214 1 1 1 1 }'));
+ENDSEC;
+DATA;
+#1 = APPLICATION_PROTOCOL_DEFINITION('international standard',
+  'automotive_design',2000,#2);
+#2 = APPLICATION_CONTEXT(
+  'core data for automotive mechanical design processes');
+#3 = SHAPE_DEFINITION_REPRESENTATION(#4,#10);
+#4 = PRODUCT_DEFINITION_SHAPE('','',#5);
+#5 = PRODUCT_DEFINITION('design','',#6,#9);
+#6 = PRODUCT_DEFINITION_FORMATION('','',#7);
+#7 = PRODUCT('Open CASCADE STEP translator 8.0 1',
+  'Open CASCADE STEP translator 8.0 1','',(#8));
+#8 = PRODUCT_CONTEXT('',#2,'mechanical');
+#9 = PRODUCT_DEFINITION_CONTEXT('part definition',#2,'design');
+#10 = ADVANCED_BREP_SHAPE_REPRESENTATION('',(#11,#15),#121);
+#11 = AXIS2_PLACEMENT_3D('',#12,#13,#14);
+#12 = CARTESIAN_POINT('',(0.,0.,0.));
+#13 = DIRECTION('',(0.,0.,1.));
+#14 = DIRECTION('',(1.,0.,-0.));
+#15 = MANIFOLD_SOLID_BREP('',#16);
+#16 = CLOSED_SHELL('',(#17,#113,#117));
+#17 = ADVANCED_FACE('',(#18),#31,.T.);
+#18 = FACE_BOUND('',#19,.T.);
+#19 = EDGE_LOOP('',(#20,#58,#81,#112));
+#20 = ORIENTED_EDGE('',*,*,#21,.F.);
+#21 = EDGE_CURVE('',#22,#22,#24,.T.);
+#22 = VERTEX_POINT('',#23);
+#23 = CARTESIAN_POINT('',(-36.4,0.,25.));
+#24 = SURFACE_CURVE('',#25,(#30,#42),.PCURVE_S1.);
+#25 = CIRCLE('',#26,36.4);
+#26 = AXIS2_PLACEMENT_3D('',#27,#28,#29);
+#27 = CARTESIAN_POINT('',(0.,0.,25.));
+#28 = DIRECTION('',(0.,0.,1.));
+#29 = DIRECTION('',(1.,0.,-0.));
+#30 = PCURVE('',#31,#36);
+#31 = CONICAL_SURFACE('',#32,36.4,0.785398163397);
+#32 = AXIS2_PLACEMENT_3D('',#33,#34,#35);
+#33 = CARTESIAN_POINT('',(0.,0.,25.));
+#34 = DIRECTION('',(0.,0.,1.));
+#35 = DIRECTION('',(1.,0.,-0.));
+#36 = DEFINITIONAL_REPRESENTATION('',(#37),#41);
+#37 = LINE('',#38,#39);
+#38 = CARTESIAN_POINT('',(-6.28318530718,3.552713678801E-15));
+#39 = VECTOR('',#40,1.);
+#40 = DIRECTION('',(1.,0.));
+#41 = ( GEOMETRIC_REPRESENTATION_CONTEXT(2) 
+PARAMETRIC_REPRESENTATION_CONTEXT() REPRESENTATION_CONTEXT('2D SPACE',''
+  ) );
+#42 = PCURVE('',#43,#48);
+#43 = PLANE('',#44);
+#44 = AXIS2_PLACEMENT_3D('',#45,#46,#47);
+#45 = CARTESIAN_POINT('',(0.,0.,25.));
+#46 = DIRECTION('',(-0.,-0.,-1.));
+#47 = DIRECTION('',(-1.,0.,0.));
+#48 = DEFINITIONAL_REPRESENTATION('',(#49),#57);
+#49 = ( BOUNDED_CURVE() B_SPLINE_CURVE(2,(#50,#51,#52,#53,#54,#55,#56),
+.UNSPECIFIED.,.T.,.F.) B_SPLINE_CURVE_WITH_KNOTS((1,2,2,2,2,1),(
+    -2.094395102393,0.,2.094395102393,4.188790204786,6.28318530718,
+8.377580409573),.UNSPECIFIED.) CURVE() GEOMETRIC_REPRESENTATION_ITEM() 
+RATIONAL_B_SPLINE_CURVE((1.,0.5,1.,0.5,1.,0.5,1.)) REPRESENTATION_ITEM(
+  '') );
+#50 = CARTESIAN_POINT('',(-36.4,0.));
+#51 = CARTESIAN_POINT('',(-36.4,63.046649395507));
+#52 = CARTESIAN_POINT('',(18.2,31.523324697754));
+#53 = CARTESIAN_POINT('',(72.8,8.915428697793E-15));
+#54 = CARTESIAN_POINT('',(18.2,-31.52332469775));
+#55 = CARTESIAN_POINT('',(-36.4,-63.0466493955));
+#56 = CARTESIAN_POINT('',(-36.4,0.));
+#57 = ( GEOMETRIC_REPRESENTATION_CONTEXT(2) 
+PARAMETRIC_REPRESENTATION_CONTEXT() REPRESENTATION_CONTEXT('2D SPACE',''
+  ) );
+#58 = ORIENTED_EDGE('',*,*,#59,.T.);
+#59 = EDGE_CURVE('',#22,#60,#62,.T.);
+#60 = VERTEX_POINT('',#61);
+#61 = CARTESIAN_POINT('',(-11.4,0.,3.552713678801E-15));
+#62 = SEAM_CURVE('',#63,(#67,#74),.PCURVE_S1.);
+#63 = LINE('',#64,#65);
+#64 = CARTESIAN_POINT('',(-36.4,0.,25.));
+#65 = VECTOR('',#66,1.);
+#66 = DIRECTION('',(0.707106781187,8.659560562349E-17,-0.707106781187));
+#67 = PCURVE('',#31,#68);
+#68 = DEFINITIONAL_REPRESENTATION('',(#69),#73);
+#69 = LINE('',#70,#71);
+#70 = CARTESIAN_POINT('',(-3.14159265359,3.552713678801E-15));
+#71 = VECTOR('',#72,1.);
+#72 = DIRECTION('',(2.13162820728E-16,-1.));
+#73 = ( GEOMETRIC_REPRESENTATION_CONTEXT(2) 
+PARAMETRIC_REPRESENTATION_CONTEXT() REPRESENTATION_CONTEXT('2D SPACE',''
+  ) );
+#74 = PCURVE('',#31,#75);
+#75 = DEFINITIONAL_REPRESENTATION('',(#76),#80);
+#76 = LINE('',#77,#78);
+#77 = CARTESIAN_POINT('',(3.14159265359,3.552713678801E-15));
+#78 = VECTOR('',#79,1.);
+#79 = DIRECTION('',(2.13162820728E-16,-1.));
+#80 = ( GEOMETRIC_REPRESENTATION_CONTEXT(2) 
+PARAMETRIC_REPRESENTATION_CONTEXT() REPRESENTATION_CONTEXT('2D SPACE',''
+  ) );
+#81 = ORIENTED_EDGE('',*,*,#82,.F.);
+#82 = EDGE_CURVE('',#60,#60,#83,.T.);
+#83 = SURFACE_CURVE('',#84,(#89,#96),.PCURVE_S1.);
+#84 = CIRCLE('',#85,11.4);
+#85 = AXIS2_PLACEMENT_3D('',#86,#87,#88);
+#86 = CARTESIAN_POINT('',(0.,0.,3.552713678801E-15));
+#87 = DIRECTION('',(0.,0.,-1.));
+#88 = DIRECTION('',(1.,0.,0.));
+#89 = PCURVE('',#31,#90);
+#90 = DEFINITIONAL_REPRESENTATION('',(#91),#95);
+#91 = LINE('',#92,#93);
+#92 = CARTESIAN_POINT('',(6.28318530718,-25.));
+#93 = VECTOR('',#94,1.);
+#94 = DIRECTION('',(-1.,0.));
+#95 = ( GEOMETRIC_REPRESENTATION_CONTEXT(2) 
+PARAMETRIC_REPRESENTATION_CONTEXT() REPRESENTATION_CONTEXT('2D SPACE',''
+  ) );
+#96 = PCURVE('',#97,#102);
+#97 = PLANE('',#98);
+#98 = AXIS2_PLACEMENT_3D('',#99,#100,#101);
+#99 = CARTESIAN_POINT('',(0.,0.,3.552713678801E-15));
+#100 = DIRECTION('',(0.,0.,1.));
+#101 = DIRECTION('',(1.,0.,-0.));
+#102 = DEFINITIONAL_REPRESENTATION('',(#103),#111);
+#103 = ( BOUNDED_CURVE() B_SPLINE_CURVE(2,(#104,#105,#106,#107,#108,#109
+,#110),.UNSPECIFIED.,.T.,.F.) B_SPLINE_CURVE_WITH_KNOTS((1,2,2,2,2,1),(
+    -2.094395102393,0.,2.094395102393,4.188790204786,6.28318530718,
+8.377580409573),.UNSPECIFIED.) CURVE() GEOMETRIC_REPRESENTATION_ITEM() 
+RATIONAL_B_SPLINE_CURVE((1.,0.5,1.,0.5,1.,0.5,1.)) REPRESENTATION_ITEM(
+  '') );
+#104 = CARTESIAN_POINT('',(11.4,0.));
+#105 = CARTESIAN_POINT('',(11.4,-19.74537920628));
+#106 = CARTESIAN_POINT('',(-5.7,-9.872689603143));
+#107 = CARTESIAN_POINT('',(-22.8,-2.792194702056E-15));
+#108 = CARTESIAN_POINT('',(-5.7,9.872689603143));
+#109 = CARTESIAN_POINT('',(11.4,19.745379206285));
+#110 = CARTESIAN_POINT('',(11.4,0.));
+#111 = ( GEOMETRIC_REPRESENTATION_CONTEXT(2) 
+PARAMETRIC_REPRESENTATION_CONTEXT() REPRESENTATION_CONTEXT('2D SPACE',''
+  ) );
+#112 = ORIENTED_EDGE('',*,*,#59,.F.);
+#113 = ADVANCED_FACE('',(#114),#43,.F.);
+#114 = FACE_BOUND('',#115,.F.);
+#115 = EDGE_LOOP('',(#116));
+#116 = ORIENTED_EDGE('',*,*,#21,.F.);
+#117 = ADVANCED_FACE('',(#118),#97,.F.);
+#118 = FACE_BOUND('',#119,.F.);
+#119 = EDGE_LOOP('',(#120));
+#120 = ORIENTED_EDGE('',*,*,#82,.F.);
+#121 = ( GEOMETRIC_REPRESENTATION_CONTEXT(3) 
+GLOBAL_UNCERTAINTY_ASSIGNED_CONTEXT((#125)) GLOBAL_UNIT_ASSIGNED_CONTEXT
+((#122,#123,#124)) REPRESENTATION_CONTEXT('Context #1',
+  '3D Context with UNIT and UNCERTAINTY') );
+#122 = ( LENGTH_UNIT() NAMED_UNIT(*) SI_UNIT(.MILLI.,.METRE.) );
+#123 = ( NAMED_UNIT(*) PLANE_ANGLE_UNIT() SI_UNIT($,.RADIAN.) );
+#124 = ( NAMED_UNIT(*) SI_UNIT($,.STERADIAN.) SOLID_ANGLE_UNIT() );
+#125 = UNCERTAINTY_MEASURE_WITH_UNIT(LENGTH_MEASURE(1.E-07),#122,
+  'distance_accuracy_value','confusion accuracy');
+#126 = PRODUCT_RELATED_PRODUCT_CATEGORY('part',$,(#7));
+ENDSEC;
+END-ISO-10303-21;
diff --git a/tests/libslic3r/test_step.cpp b/tests/libslic3r/test_step.cpp
index 0bb83f5809..5d843499fa 100644
--- a/tests/libslic3r/test_step.cpp
+++ b/tests/libslic3r/test_step.cpp
@@ -8,6 +8,7 @@
 #include <catch2/generators/catch_generators.hpp>
 #include "libslic3r/Model.hpp"
 #include "libslic3r/Format/STEP.hpp"
+#include "libslic3r/TriangleMesh.hpp"
 #include "test_utils.hpp"
 
 using namespace Slic3r;
@@ -73,6 +74,23 @@ TEST_CASE("A security classification assignment does not crash import", "[Step]"
     CHECK(model.objects.front()->volumes.front()->mesh().facets_count() == 4); // a tetrahedron
 }
 
+// The fixture is a truncated cone whose seam pcurves have the direction (2.1e-16, -1).
+TEST_CASE("A cone with a slightly tilted seam imports as a closed mesh", "[Step]")
+{
+    const std::string path = std::string(TEST_DATA_DIR) + PATH_SEPARATOR "cone_tilted_seam_pcurve.step";
+
+    Model model;
+    bool  cancel = false;
+    Step  step(path);
+
+    REQUIRE(step.load() == Step::Step_Status::LOAD_SUCCESS);
+    REQUIRE(step.mesh(&model, cancel, false) == Step::Step_Status::MESH_SUCCESS);
+
+    REQUIRE(model.objects.size() == 1);
+    REQUIRE(model.objects.front()->volumes.size() == 1);
+    CHECK(its_num_open_edges(model.objects.front()->volumes.front()->mesh().its) == 0);
+}
+
 TEST_CASE("isUtf8 recognises two, three and four byte sequences", "[Step]")
 {
     CHECK(StepPreProcessor::isUtf8("\xC3\xA9"));         // U+00E9