Replacing Mixin1D.discretize with enhanced Minxin1D.positions

src/build123d/topology/one_d.py

@@ -120,6 +120,9 @@ from OCP.GeomAbs import (
     GeomAbs_C0,
     GeomAbs_C1,
     GeomAbs_C2,
+    GeomAbs_C3,
+    GeomAbs_CN,
+    GeomAbs_C1,
     GeomAbs_G1,
     GeomAbs_G2,
     GeomAbs_JoinType,
@@ -545,31 +548,6 @@ class Mixin1D(Shape[TOPODS]):
 
         return result
 
-    def discretize(self, deflection: float = 0.1, quasi=True) -> list[Vector]:
-        """Discretize the shape into a list of points"""
-        if self.wrapped is None:
-            raise ValueError("Cannot discretize an empty shape")
-        curve = self.geom_adaptor()
-        if quasi:
-            discretizer = GCPnts_QuasiUniformDeflection()
-        else:
-            discretizer = GCPnts_UniformDeflection()
-        discretizer.Initialize(
-            curve,
-            deflection,
-            curve.FirstParameter(),
-            curve.LastParameter(),
-        )
-
-        assert discretizer.IsDone()
-
-        return [
-            Vector(v.X(), v.Y(), v.Z())
-            for v in (
-                curve.Value(discretizer.Parameter(i))
-                for i in range(1, discretizer.NbPoints() + 1)
-            )
-        ]
     def curvature_comb(
         self, count: int = 100, max_tooth_size: float | None = None
     ) -> ShapeList[Edge]:
@@ -1207,22 +1185,52 @@ class Mixin1D(Shape[TOPODS]):
 
     def positions(
         self,
-        distances: Iterable[float],
+        distances: Iterable[float] | None = None,
         position_mode: PositionMode = PositionMode.PARAMETER,
+        deflection: float | None = None,
     ) -> list[Vector]:
         """Positions along curve
 
         Generate positions along the underlying curve
 
         Args:
-            distances (Iterable[float]): distance or parameter values
-            position_mode (PositionMode, optional): position calculation mode.
-                Defaults to PositionMode.PARAMETER.
+            distances (Iterable[float] | None, optional): distance or parameter values.
+                Defaults to None.
+            position_mode (PositionMode, optional): position calculation mode only applies
+                when using distances. Defaults to PositionMode.PARAMETER.
+            deflection (float | None, optional): maximum deflection between the curve and
+                the polygon that results from the computed points. Defaults to None.
+
 
         Returns:
             list[Vector]: positions along curve
         """
+        if deflection is not None:
+            curve: BRepAdaptor_Curve | BRepAdaptor_CompCurve = self.geom_adaptor()
+            # GCPnts_UniformDeflection provides the best results but is limited
+            if curve.Continuity() in (GeomAbs_C2, GeomAbs_C3, GeomAbs_CN):
+                discretizer: (
+                    GCPnts_UniformDeflection | GCPnts_QuasiUniformDeflection
+                ) = GCPnts_UniformDeflection()
+            else:
+                discretizer = GCPnts_QuasiUniformDeflection()
+
+            discretizer.Initialize(
+                curve,
+                deflection,
+                curve.FirstParameter(),
+                curve.LastParameter(),
+            )
+            if not discretizer.IsDone() or discretizer.NbPoints() == 0:
+                raise RuntimeError("Deflection calculation failed")
+            return [
+                Vector(curve.Value(discretizer.Parameter(i + 1)))
+                for i in range(discretizer.NbPoints())
+            ]
+        elif distances is not None:
             return [self.position_at(d, position_mode) for d in distances]
+        else:
+            raise ValueError("Either distances or deflection must be provided")
 
     def project(
         self, face: Face, direction: VectorLike, closest: bool = True

tests/test_direct_api/test_mixin1_d.py

@@ -28,6 +28,7 @@ license:
 
 import math
 import unittest
+from unittest.mock import patch
 
 from build123d.build_enums import (
     CenterOf,
@@ -106,13 +107,73 @@ class TestMixin1D(unittest.TestCase):
             5,
         )
 
-    def test_positions(self):
+    def test_positions_with_distances(self):
         e = Edge.make_line((0, 0, 0), (1, 1, 1))
         distances = [i / 4 for i in range(3)]
         pts = e.positions(distances)
         for i, position in enumerate(pts):
             self.assertAlmostEqual(position, (i / 4, i / 4, i / 4), 5)
 
+    def test_positions_deflection_line(self):
+        """Deflection sampling on a straight line should yield exactly 2 points."""
+        e = Edge.make_line((0, 0, 0), (10, 0, 0))
+        pts = e.positions(deflection=0.1)
+
+        self.assertEqual(len(pts), 2)
+        self.assertAlmostEqual(pts[0], (0, 0, 0), 7)
+        self.assertAlmostEqual(pts[1], (10, 0, 0), 7)
+
+    def test_positions_deflection_circle(self):
+        """Deflection on a C2 curve (circle) should produce multiple points."""
+        radius = 5
+        e = Edge.make_circle(radius)
+
+        pts = e.positions(deflection=0.1)
+
+        # Should produce more than just two points
+        self.assertGreater(len(pts), 2)
+
+        # Endpoints should match curve endpoints
+        first, last = pts[0], pts[-1]
+        curve = e.geom_adaptor()
+        p0 = Vector(curve.Value(curve.FirstParameter()))
+        p1 = Vector(curve.Value(curve.LastParameter()))
+
+        self.assertAlmostEqual(first, p0, 7)
+        self.assertAlmostEqual(last, p1, 7)
+
+    def test_positions_deflection_resolution(self):
+        """Smaller deflection tolerance should produce more points."""
+        e = Edge.make_circle(10)
+
+        pts_coarse = e.positions(deflection=0.5)
+        pts_fine = e.positions(deflection=0.05)
+
+        self.assertGreater(len(pts_fine), len(pts_coarse))
+
+    def test_positions_deflection_C0_curve(self):
+        """C0 spline should use QuasiUniformDeflection and still succeed."""
+        e = Polyline((0, 0), (1, 2), (2, 0))._to_bspline()  # C0
+        pts = e.positions(deflection=0.1)
+
+        self.assertGreater(len(pts), 2)
+
+    def test_positions_missing_arguments(self):
+        e = Edge.make_line((0, 0, 0), (1, 0, 0))
+        with self.assertRaises(ValueError):
+            e.positions()
+
+    def test_positions_deflection_failure(self):
+        e = Edge.make_circle(1.0)
+
+        with patch("build123d.topology.one_d.GCPnts_UniformDeflection") as MockDefl:
+            instance = MockDefl.return_value
+            instance.IsDone.return_value = False
+            instance.NbPoints.return_value = 0
+
+            with self.assertRaises(RuntimeError):
+                e.positions(deflection=0.1)
+
     def test_tangent_at(self):
         self.assertAlmostEqual(
             Edge.make_circle(1, start_angle=0, end_angle=90).tangent_at(1.0),
@@ -368,11 +429,6 @@ class TestMixin1D(unittest.TestCase):
         self.assertAlmostEqual(common.z_dir.Y, 0, 5)
         self.assertAlmostEqual(common.z_dir.Z, 0, 5)
 
-    def test_discretize(self):
-        edge = Edge.make_circle(2, start_angle=0, end_angle=180)
-        points = edge.discretize(0.1)
-        self.assertEqual(len(points), 6)
-
     def test_edge_volume(self):
         edge = Edge.make_line((0, 0), (1, 1))
         self.assertAlmostEqual(edge.volume, 0, 5)