anchors

core/slice.py

@@ -2063,6 +2063,26 @@ def _walk_along_path(
     return clean_pts
 
 
+def _get_anchor_walk_dir(c: np.ndarray, reverse: bool = False) -> int:
+    """
+    Returns the step direction along c (+1 or -1) to follow the path clockwise.
+    If c is closed:
+      - CCW polygon (signed area > 0): index -1 is clockwise.
+      - CW polygon (signed area < 0): index +1 is clockwise.
+    If reverse is True, inverts the direction (counter-clockwise).
+    If c is open, defaults to +1 (or -1 if reverse).
+    """
+    if not is_closed_path(c) or len(c) < 3:
+        return -1 if reverse else 1
+
+    pts_2d = c[:, :2]
+    signed_area = np.sum(pts_2d[:-1, 0] * pts_2d[1:, 1] - pts_2d[1:, 0] * pts_2d[:-1, 1])
+    is_ccw = signed_area > 0
+
+    cw_dir = -1 if is_ccw else 1
+    return -cw_dir if reverse else cw_dir
+
+
 def anchor_paths(
     paths: SlicePaths,
     anchor_paths: SlicePaths | list[np.ndarray],
@@ -2072,8 +2092,10 @@ def anchor_paths(
 ) -> SlicePaths:
     """
     Extends open paths in paths where their start/end vertices touch anchor_paths
-    by following the anchor path for the specified distance.
-    If reverse is True, follows the anchor path in the reverse direction.
+    by following the anchor path in the clockwise direction for the specified distance.
+    If reverse is True, follows the anchor path in the counter-clockwise direction.
+    Both start and end vertices extend clockwise along the touched path, ignoring the
+    internal orientation of the open path.
     Closed paths and open paths that do not touch anchor_paths remain untouched.
     """
     if not paths or not anchor_paths or distance <= 1e-7:
@@ -2110,8 +2132,8 @@ def anchor_paths(
             z_val = float(p[0, 2]) if p.shape[1] > 2 else 0.0
             p_touch[2] = z_val
             p[0] = p_touch.copy()
-            dir_from_p = 1 if reverse else -1
-            walked = _walk_along_path(c, seg_idx, t_val, p_touch, distance, dir_from_p, is_c_closed, z_val)
+            dir_walk = _get_anchor_walk_dir(c, reverse=reverse)
+            walked = _walk_along_path(c, seg_idx, t_val, p_touch, distance, dir_walk, is_c_closed, z_val)
             walked = [pt for pt in walked if np.linalg.norm(pt[:2] - p[0, :2]) > 1e-5]
             if walked:
                 prefix = walked[::-1]
@@ -2125,8 +2147,8 @@ def anchor_paths(
             z_val = float(p[-1, 2]) if p.shape[1] > 2 else 0.0
             p_touch[2] = z_val
             p[-1] = p_touch.copy()
-            dir_from_p = -1 if reverse else 1
-            walked = _walk_along_path(c, seg_idx, t_val, p_touch, distance, dir_from_p, is_c_closed, z_val)
+            dir_walk = _get_anchor_walk_dir(c, reverse=reverse)
+            walked = _walk_along_path(c, seg_idx, t_val, p_touch, distance, dir_walk, is_c_closed, z_val)
             walked = [pt for pt in walked if np.linalg.norm(pt[:2] - p[-1, :2]) > 1e-5]
             if walked:
                 postfix = walked

tests/test_anchor_paths.py

@@ -94,16 +94,16 @@ class TestAnchorPaths(unittest.TestCase):
         self.assertEqual(len(res), 1)
         p = res[0]
 
-        # reverse=False follows anchor in forward (+1) direction:
+        # reverse=False follows anchor clockwise for both endpoints:
         # Start vertex (5,0) touches bottom edge (0->10).
-        # Forward is +X, so nozzle enters from (3,0) to (5,0).
+        # Clockwise is -X (towards 0,0), so extension goes to (3,0).
         # End vertex (5,10) touches top edge (10->0).
-        # Forward is -X, so nozzle exits from (5,10) to (3,10).
+        # Clockwise is +X (towards 10,10), so extension goes to (7,10).
         self.assertEqual(len(p), 4)
         np.testing.assert_allclose(p[0], [3.0, 0.0, 0.2], atol=1e-5)
         np.testing.assert_allclose(p[1], [5.0, 0.0, 0.2], atol=1e-5)
         np.testing.assert_allclose(p[2], [5.0, 10.0, 0.2], atol=1e-5)
-        np.testing.assert_allclose(p[3], [3.0, 10.0, 0.2], atol=1e-5)
+        np.testing.assert_allclose(p[3], [7.0, 10.0, 0.2], atol=1e-5)
 
     def test_anchor_both_ends_reverse(self):
         infill = np.array([[5.0, 0.0, 0.2], [5.0, 10.0, 0.2]], dtype=np.float64)
@@ -113,14 +113,14 @@ class TestAnchorPaths(unittest.TestCase):
         self.assertEqual(len(res), 1)
         p = res[0]
 
-        # reverse=True follows anchor in opposite (-1) direction:
-        # Start vertex (5,0): opposite of +X is -X, so nozzle enters from (7,0) to (5,0).
-        # End vertex (5,10): opposite of -X is +X, so nozzle exits from (5,10) to (7,10).
+        # reverse=True follows anchor counter-clockwise for both endpoints:
+        # Start vertex (5,0): counter-clockwise is +X (towards 10,0) -> (7,0).
+        # End vertex (5,10): counter-clockwise is -X (towards 0,10) -> (3,10).
         self.assertEqual(len(p), 4)
         np.testing.assert_allclose(p[0], [7.0, 0.0, 0.2], atol=1e-5)
         np.testing.assert_allclose(p[1], [5.0, 0.0, 0.2], atol=1e-5)
         np.testing.assert_allclose(p[2], [5.0, 10.0, 0.2], atol=1e-5)
-        np.testing.assert_allclose(p[3], [7.0, 10.0, 0.2], atol=1e-5)
+        np.testing.assert_allclose(p[3], [3.0, 10.0, 0.2], atol=1e-5)
 
     def test_anchor_start_only(self):
         # Infill touching only at start: (5,0) to (5,5)
@@ -130,7 +130,7 @@ class TestAnchorPaths(unittest.TestCase):
         res = sp.anchor(self.anchor_sp, distance=2.0, reverse=False)
         self.assertEqual(len(res), 1)
         p = res[0]
-        # Only start prepended
+        # Only start prepended (clockwise on bottom edge -> (3,0))
         self.assertEqual(len(p), 3)
         np.testing.assert_allclose(p[0], [3.0, 0.0, 0.2], atol=1e-5)
         np.testing.assert_allclose(p[1], [5.0, 0.0, 0.2], atol=1e-5)
@@ -144,11 +144,11 @@ class TestAnchorPaths(unittest.TestCase):
         res = sp.anchor(self.anchor_sp, distance=2.0, reverse=False)
         self.assertEqual(len(res), 1)
         p = res[0]
-        # Only end appended
+        # Only end appended (clockwise on top edge -> (7,10))
         self.assertEqual(len(p), 3)
         np.testing.assert_allclose(p[0], [5.0, 5.0, 0.2], atol=1e-5)
         np.testing.assert_allclose(p[1], [5.0, 10.0, 0.2], atol=1e-5)
-        np.testing.assert_allclose(p[2], [3.0, 10.0, 0.2], atol=1e-5)
+        np.testing.assert_allclose(p[2], [7.0, 10.0, 0.2], atol=1e-5)
 
     def test_anchor_closed_path_ignored(self):
         # A closed square inside
@@ -168,19 +168,39 @@ class TestAnchorPaths(unittest.TestCase):
         # Infill starts at (1, 0, 0.2) and goes to (1, 10, 0.2)
         # Distance = 3.0, reverse = False
         # Bottom edge is (0,0) -> (10,0).
-        # Walking backward (-1) from (1,0) reaches (0,0) after 1.0mm.
-        # Remaining 2.0mm continues onto left edge (0,10) -> (0,0).
-        # Walking backward along left edge means going South from (0,0) towards (0,10),
-        # which reaches (0, 2, 0.2).
-        # Prefix reversed: [(0, 2), (0, 0)]
+        # Clockwise is -X: from (1,0) reaches (0,0) after 1.0mm.
+        # Remaining 2.0mm continues onto left edge towards (0,10) (North, +Y), reaching (0, 2, 0.2).
+        # Top edge is (10,10) -> (0,10).
+        # Clockwise is +X: from (1,10) reaches (4,10) after 3.0mm.
         infill = np.array([[1.0, 0.0, 0.2], [1.0, 10.0, 0.2]], dtype=np.float64)
         sp = SlicePaths([infill])
 
         res = sp.anchor(self.anchor_sp, distance=3.0, reverse=False)
         p = res[0]
+        self.assertEqual(len(p), 5)
         np.testing.assert_allclose(p[0], [0.0, 2.0, 0.2], atol=1e-5)
         np.testing.assert_allclose(p[1], [0.0, 0.0, 0.2], atol=1e-5)
         np.testing.assert_allclose(p[2], [1.0, 0.0, 0.2], atol=1e-5)
+        np.testing.assert_allclose(p[3], [1.0, 10.0, 0.2], atol=1e-5)
+        np.testing.assert_allclose(p[4], [4.0, 10.0, 0.2], atol=1e-5)
+
+    def test_anchor_open_path_direction_invariant(self):
+        # Verifies that both A->B and B->A extend in the exact same clockwise direction
+        line_fwd = np.array([[5.0, 0.0, 0.2], [5.0, 10.0, 0.2]], dtype=np.float64)
+        line_rev = np.array([[5.0, 10.0, 0.2], [5.0, 0.0, 0.2]], dtype=np.float64)
+
+        res_fwd = SlicePaths([line_fwd]).anchor(self.anchor_sp, distance=2.0, reverse=False)
+        res_rev = SlicePaths([line_rev]).anchor(self.anchor_sp, distance=2.0, reverse=False)
+
+        # For fwd: start at (5,0) extends to (3,0); end at (5,10) extends to (7,10)
+        p_fwd = res_fwd[0]
+        np.testing.assert_allclose(p_fwd[0], [3.0, 0.0, 0.2], atol=1e-5)
+        np.testing.assert_allclose(p_fwd[-1], [7.0, 10.0, 0.2], atol=1e-5)
+
+        # For rev: start at (5,10) extends to (7,10); end at (5,0) extends to (3,0)
+        p_rev = res_rev[0]
+        np.testing.assert_allclose(p_rev[0], [7.0, 10.0, 0.2], atol=1e-5)
+        np.testing.assert_allclose(p_rev[-1], [3.0, 0.0, 0.2], atol=1e-5)
 
     def test_anchor_layer_mismatch_ignored(self):
         # Infill on layer Z = 0.4, anchor on layer Z = 0.2

tests/visual/visualize_anchor_paths.py

@@ -116,17 +116,17 @@ def generate_single_line_comparison() -> str:
     res_fwd = infill_sp.anchor(boundary_sp, distance=2.5, reverse=False)
     p_fwd = res_fwd[0]
     ax2 = axes[1]
-    ax2.set_title("2. Anchored (Reverse = False)\nFollows Forward (+1) Traversal", fontsize=11, fontweight='bold', pad=10)
+    ax2.set_title("2. Anchored (Reverse = False)\nBoth Ends Follow Clockwise Traversal", fontsize=11, fontweight='bold', pad=10)
     ax2.plot(square[:, 0], square[:, 1], color='#1f77b4', linestyle='--', linewidth=1.5, alpha=0.5, label="Anchor Perimeter")
     # Draw original in light grey
     ax2.plot(infill[:, 0], infill[:, 1], color='gray', linestyle=':', linewidth=1.5, alpha=0.6)
     # Draw anchored path with directional arrows
     draw_path_with_arrows(ax2, p_fwd, color='#2ca02c', label="Anchored Path", linewidth=2.5)
     # Highlight start anchor and end anchor
-    ax2.plot(p_fwd[:2, 0], p_fwd[:2, 1], color='#9467bd', linewidth=3.5, label="Start Anchor (Prepended)")
-    ax2.plot(p_fwd[-2:, 0], p_fwd[-2:, 1], color='#d62728', linewidth=3.5, label="End Anchor (Appended)")
-    ax2.plot(p_fwd[0, 0], p_fwd[0, 1], 'g^', markersize=10, label="New Start (2.5mm before)")
-    ax2.plot(p_fwd[-1, 0], p_fwd[-1, 1], 'rs', markersize=9, label="New End (2.5mm after)")
+    ax2.plot(p_fwd[:2, 0], p_fwd[:2, 1], color='#9467bd', linewidth=3.5, label="Start Anchor (Clockwise)")
+    ax2.plot(p_fwd[-2:, 0], p_fwd[-2:, 1], color='#d62728', linewidth=3.5, label="End Anchor (Clockwise)")
+    ax2.plot(p_fwd[0, 0], p_fwd[0, 1], 'g^', markersize=10, label="New Start (2.5mm CW)")
+    ax2.plot(p_fwd[-1, 0], p_fwd[-1, 1], 'rs', markersize=9, label="New End (2.5mm CW)")
     ax2.set_xlim(-1, 11)
     ax2.set_ylim(-1, 11)
     ax2.set_aspect('equal')
@@ -137,7 +137,7 @@ def generate_single_line_comparison() -> str:
     res_rev = infill_sp.anchor(boundary_sp, distance=2.5, reverse=True)
     p_rev = res_rev[0]
     ax3 = axes[2]
-    ax3.set_title("3. Anchored (Reverse = True)\nFollows Opposite (-1) Traversal", fontsize=11, fontweight='bold', pad=10)
+    ax3.set_title("3. Anchored (Reverse = True)\nBoth Ends Follow Counter-Clockwise Traversal", fontsize=11, fontweight='bold', pad=10)
     ax3.plot(square[:, 0], square[:, 1], color='#1f77b4', linestyle='--', linewidth=1.5, alpha=0.5, label="Anchor Perimeter")
     ax3.plot(infill[:, 0], infill[:, 1], color='gray', linestyle=':', linewidth=1.5, alpha=0.6)
     draw_path_with_arrows(ax3, p_rev, color='#e377c2', label="Anchored Path", linewidth=2.5)