fix bezier approximation

Author: snoyer

ocpsvg/ocp.py

@@ -11,6 +11,7 @@
 from OCP.BRepFeat import BRepFeat
 from OCP.BRepLib import BRepLib_FindSurface
 from OCP.BRepTools import BRepTools
+from OCP.Convert import Convert_ParameterisationType
 from OCP.GC import (
     GC_MakeArcOfCircle,
     GC_MakeArcOfEllipse,
@@ -357,7 +358,7 @@ def ellipse_curve(
 
 
 def curve_to_bspline(curve: Geom_Curve) -> Geom_BSplineCurve:
-    return GeomConvert.CurveToBSplineCurve_s(curve)  # type: ignore
+    return GeomConvert.CurveToBSplineCurve_s(curve, Convert_ParameterisationType.Convert_RationalC1)  # type: ignore
 
 
 def curve_to_beziers(
@@ -399,8 +400,10 @@ def curve_to_beziers(
         )
 
     else:
+        bspline = curve_to_bspline(curve)
+        bspline.Segment(adaptor.FirstParameter(), adaptor.LastParameter())
         yield from bspline_to_beziers(
-            curve_to_bspline(curve),
+            bspline,
             max_degree=max_degree,
             max_segments=max_segments,
             tolerance=tolerance,

ocpsvg/svg.py

@@ -573,6 +573,8 @@ def curve_to_svg_path(
             beziers = curve_to_beziers(
                 adaptor, tolerance=tolerance, max_degree=3 if use_cubics else 2
             )
+            if reverse:
+                beziers = reversed(list(beziers))
             for i, bezier in enumerate(beziers):
                 yield from bezier_to_svg_path(
                     bezier,

tests/test_svg.py

@@ -9,9 +9,10 @@
 
 import pytest
 import svgelements
+from OCP.GC import GC_MakeArcOfCircle
 from OCP.Geom import Geom_Circle, Geom_Curve, Geom_Ellipse, Geom_TrimmedCurve
 from OCP.GeomAbs import GeomAbs_CurveType
-from OCP.gp import gp_Pnt, gp_Vec
+from OCP.gp import gp_Ax2, gp_Circ, gp_Pnt, gp_Vec
 from OCP.TopoDS import TopoDS, TopoDS_Edge, TopoDS_Face, TopoDS_Shape, TopoDS_Wire
 from pytest import approx, raises
 
@@ -33,6 +34,7 @@
     SvgPathCommand,
     _SegmentInPath,  # type: ignore private usage
     bezier_to_svg_path,
+    curve_to_svg_path,
     edge_to_svg_path,
     edges_from_svg_path,
     face_to_svg_path,
@@ -159,6 +161,44 @@ def test_polyline_apprx(curve: Geom_Curve):
     assert set(seg[0] for seg in path).issubset(set("MLZ"))
 
 
+def test_trimmed_arc_to_cubics():
+    radius = 10
+    circ = gp_Circ(gp_Ax2(), radius)
+    trimmed_arc = GC_MakeArcOfCircle(
+        circ, gp_Pnt(-radius, 0, 0), gp_Pnt(0, +radius, 0), True
+    ).Value()
+
+    svg_with_arcs = list(curve_to_svg_path(trimmed_arc, tolerance=1e-6))
+    svg_with_cubics_only = list(
+        curve_to_svg_path(
+            trimmed_arc, use_arcs=False, use_quadratics=False, tolerance=1e-6
+        )
+    )
+    assert svg_with_arcs[0][-2:] == approx(svg_with_cubics_only[0][-2:])
+    assert svg_with_arcs[-1][-2:] == approx(svg_with_cubics_only[-1][-2:])
+
+
+def test_trimmed_arc_to_cubics_reversed():
+    radius = 10
+    circ = gp_Circ(gp_Ax2(), radius)
+    trimmed_arc = GC_MakeArcOfCircle(
+        circ, gp_Pnt(-radius, 0, 0), gp_Pnt(0, +radius, 0), True
+    ).Value()
+
+    svg_with_arcs = list(curve_to_svg_path(trimmed_arc, reverse=True, tolerance=1e-6))
+    svg_with_cubics_only = list(
+        curve_to_svg_path(
+            trimmed_arc,
+            reverse=True,
+            use_arcs=False,
+            use_quadratics=False,
+            tolerance=1e-6,
+        )
+    )
+    assert svg_with_arcs[0][-2:] == approx(svg_with_cubics_only[0][-2:])
+    assert svg_with_arcs[-1][-2:] == approx(svg_with_cubics_only[-1][-2:])
+
+
 @pytest.mark.parametrize(
     "wire, svg_d, opts",
     [