[remove_colinear_vertices / Path] add preserve_uturns and use it for paths

masque/shapes/path.py

@@ -323,9 +323,30 @@ class Path(Shape):
             ) -> list['Polygon']:
         extensions = self._calculate_cap_extensions()
 
-        v = remove_colinear_vertices(self.vertices, closed_path=False)
+        v = remove_colinear_vertices(self.vertices, closed_path=False, preserve_uturns=True)
         dv = numpy.diff(v, axis=0)
-        dvdir = dv / numpy.sqrt((dv * dv).sum(axis=1))[:, None]
+        norms = numpy.sqrt((dv * dv).sum(axis=1))
+
+        # Filter out zero-length segments if any remained after remove_colinear_vertices
+        valid = (norms > 1e-18)
+        if not numpy.all(valid):
+            # This shouldn't happen much if remove_colinear_vertices is working
+            v = v[numpy.append(valid, True)]
+            dv = numpy.diff(v, axis=0)
+            norms = norms[valid]
+
+        if dv.shape[0] == 0:
+            # All vertices were the same. It's a point.
+            if self.width == 0:
+                return [Polygon(vertices=numpy.zeros((3, 2)))] # Area-less degenerate
+            if self.cap == PathCap.Circle:
+                return Circle(radius=self.width / 2, offset=v[0]).to_polygons(num_vertices=num_vertices, max_arclen=max_arclen)
+            if self.cap == PathCap.Square:
+                return [Polygon.square(side_length=self.width, offset=v[0])]
+            # Flush or CustomSquare
+            return [Polygon(vertices=numpy.zeros((3, 2)))]
+
+        dvdir = dv / norms[:, None]
 
         if self.width == 0:
             verts = numpy.vstack((v, v[::-1]))
@@ -448,16 +469,11 @@ class Path(Shape):
         rotated_vertices = numpy.vstack([numpy.dot(rotation_matrix_2d(-rotation), v)
                                         for v in normed_vertices])
 
-        # Reorder the vertices so that the one with lowest x, then y, comes first.
-        x_min_val = rotated_vertices[:, 0].min()
-        x_min_inds = numpy.where(rotated_vertices[:, 0] == x_min_val)[0]
-        if x_min_inds.size > 1:
-            y_min_val = rotated_vertices[x_min_inds, 1].min()
-            tie_breaker = numpy.where(rotated_vertices[x_min_inds, 1] == y_min_val)[0][0]
-            start_ind = x_min_inds[tie_breaker]
+        # Canonical ordering for open paths: pick whichever of (v) or (v[::-1]) is smaller
+        if tuple(rotated_vertices.flat) > tuple(rotated_vertices[::-1].flat):
+            reordered_vertices = rotated_vertices[::-1]
         else:
-            start_ind = x_min_inds[0]
-        reordered_vertices = numpy.roll(rotated_vertices, -start_ind, axis=0)
+            reordered_vertices = rotated_vertices
 
         width0 = self.width / norm_value
 
@@ -496,7 +512,7 @@ class Path(Shape):
         Returns:
             self
         """
-        self.vertices = remove_colinear_vertices(self.vertices, closed_path=False)
+        self.vertices = remove_colinear_vertices(self.vertices, closed_path=False, preserve_uturns=True)
         return self
 
     def _calculate_cap_extensions(self) -> NDArray[numpy.float64]:

masque/test/test_utils.py

@@ -29,14 +29,19 @@ def test_remove_colinear_vertices() -> None:
 def test_remove_colinear_vertices_exhaustive() -> None:
     # U-turn
     v = [[0, 0], [10, 0], [0, 0]]
-    v_clean = remove_colinear_vertices(v, closed_path=False)
+    v_clean = remove_colinear_vertices(v, closed_path=False, preserve_uturns=True)
     # Open path should keep ends. [10,0] is between [0,0] and [0,0]?
-    # Yes, they are all on the same line.
-    assert len(v_clean) == 2
+    # They are colinear, but it's a 180 degree turn.
+    # We preserve 180 degree turns if preserve_uturns is True.
+    assert len(v_clean) == 3
+
+    v_collapsed = remove_colinear_vertices(v, closed_path=False, preserve_uturns=False)
+    # If not preserving u-turns, it should collapse to just the endpoints
+    assert len(v_collapsed) == 2
 
     # 180 degree U-turn in closed path
     v = [[0, 0], [10, 0], [5, 0]]
-    v_clean = remove_colinear_vertices(v, closed_path=True)
+    v_clean = remove_colinear_vertices(v, closed_path=True, preserve_uturns=False)
     assert len(v_clean) == 2
 
 

masque/utils/vertices.py

@@ -30,7 +30,11 @@ def remove_duplicate_vertices(vertices: ArrayLike, closed_path: bool = True) ->
     return result
 
 
-def remove_colinear_vertices(vertices: ArrayLike, closed_path: bool = True) -> NDArray[numpy.float64]:
+def remove_colinear_vertices(
+        vertices: ArrayLike,
+        closed_path: bool = True,
+        preserve_uturns: bool = False,
+        ) -> NDArray[numpy.float64]:
     """
     Given a list of vertices, remove any superflous vertices (i.e.
         those which lie along the line formed by their neighbors)
@@ -39,6 +43,8 @@ def remove_colinear_vertices(vertices: ArrayLike, closed_path: bool = True) -> N
         vertices: Nx2 ndarray of vertices
         closed_path: If `True`, the vertices are assumed to represent an implicitly
            closed path. If `False`, the path is assumed to be open. Default `True`.
+        preserve_uturns: If `True`, colinear vertices that correspond to a 180 degree
+           turn (a "spike") are preserved. Default `False`.
 
     Returns:
         `vertices` with colinear (superflous) vertices removed. May be a view into the original array.
@@ -46,14 +52,24 @@ def remove_colinear_vertices(vertices: ArrayLike, closed_path: bool = True) -> N
     vertices = remove_duplicate_vertices(vertices, closed_path=closed_path)
 
     # Check for dx0/dy0 == dx1/dy1
+    dv = numpy.roll(vertices, -1, axis=0) - vertices
+    if not closed_path:
+        dv[-1] = 0
 
-    dv = numpy.roll(vertices, -1, axis=0) - vertices  # [y1-y0, y2-y1, ...]
-    dxdy = dv * numpy.roll(dv, 1, axis=0)[:, ::-1]    # [[dx0*(dy_-1), (dx_-1)*dy0], dx1*dy0, dy1*dx0]]
+    # dxdy[i] is based on dv[i] and dv[i-1]
+    # slopes_equal[i] refers to vertex i
+    dxdy = dv * numpy.roll(dv, 1, axis=0)[:, ::-1]
 
     dxdy_diff = numpy.abs(numpy.diff(dxdy, axis=1))[:, 0]
     err_mult = 2 * numpy.abs(dxdy).sum(axis=1) + 1e-40
 
     slopes_equal = (dxdy_diff / err_mult) < 1e-15
+
+    if preserve_uturns:
+        # Only merge if segments are in the same direction (avoid collapsing u-turns)
+        dot_prod = (dv * numpy.roll(dv, 1, axis=0)).sum(axis=1)
+        slopes_equal &= (dot_prod > 0)
+
     if not closed_path:
         slopes_equal[[0, -1]] = False