Add comprehensive tests for edge depth extension, empty image edits, and material view adaptation

- Introduced `test_edge_depth.py` to validate the functionality of edge depth extension, ensuring core alpha preservation, proper depth handling, and edge padding behavior.
- Created `test_empty_image_edits.py` to verify the behavior of image edits in Blender, focusing on shared edits, preservation of image properties, and handling of failed operations.
- Developed `test_material_view_adaptation.py` to test material adaptation preferences, ensuring color space and alpha settings are correctly applied and preserved across various scenarios.

src/anyimage/operators/cutout_tool/polygon.py

@@ -0,0 +1,94 @@
+"""Polygonal chain simplification using NumPy."""
+
+import numpy as np
+
+
+# approximate_polygon: scikit-image 0.25.2, copyright 2009-2022 the scikit-image team.
+# BSD-3-Clause; see ../../licenses/scikit-image.txt.
+def approximate_polygon(coords, tolerance):
+    """Approximate a polygonal chain with the specified tolerance.
+
+    It is based on the Douglas-Peucker algorithm.
+
+    Note that the approximated polygon is always within the convex hull of the
+    original polygon.
+
+    Parameters
+    ----------
+    coords : (K, 2) array
+        Coordinate array.
+    tolerance : float
+        Maximum distance from original points of polygon to approximated
+        polygonal chain. If tolerance is 0, the original coordinate array
+        is returned.
+
+    Returns
+    -------
+    coords : (L, 2) array
+        Approximated polygonal chain where L <= K.
+
+    References
+    ----------
+    .. [1] https://en.wikipedia.org/wiki/Ramer-Douglas-Peucker_algorithm
+    """
+    if tolerance <= 0:
+        return coords
+
+    chain = np.zeros(coords.shape[0], "bool")
+    # pre-allocate distance array for all points
+    dists = np.zeros(coords.shape[0])
+    chain[0] = True
+    chain[-1] = True
+    pos_stack = [(0, chain.shape[0] - 1)]
+    end_of_chain = False
+
+    while not end_of_chain:
+        start, end = pos_stack.pop()
+        # determine properties of current line segment
+        r0, c0 = coords[start, :]
+        r1, c1 = coords[end, :]
+        dr = r1 - r0
+        dc = c1 - c0
+        segment_angle = -np.arctan2(dr, dc)
+        segment_dist = c0 * np.sin(segment_angle) + r0 * np.cos(segment_angle)
+
+        # select points in-between line segment
+        segment_coords = coords[start + 1 : end, :]
+        segment_dists = dists[start + 1 : end]
+
+        # check whether to take perpendicular or euclidean distance with
+        # inner product of vectors
+
+        # vectors from points -> start and end
+        dr0 = segment_coords[:, 0] - r0
+        dc0 = segment_coords[:, 1] - c0
+        dr1 = segment_coords[:, 0] - r1
+        dc1 = segment_coords[:, 1] - c1
+        # vectors points -> start and end projected on start -> end vector
+        projected_lengths0 = dr0 * dr + dc0 * dc
+        projected_lengths1 = -dr1 * dr - dc1 * dc
+        perp = np.logical_and(projected_lengths0 > 0, projected_lengths1 > 0)
+        eucl = np.logical_not(perp)
+        segment_dists[perp] = np.abs(
+            segment_coords[perp, 0] * np.cos(segment_angle)
+            + segment_coords[perp, 1] * np.sin(segment_angle)
+            - segment_dist
+        )
+        segment_dists[eucl] = np.minimum(
+            # distance to start point
+            np.sqrt(dc0[eucl] ** 2 + dr0[eucl] ** 2),
+            # distance to end point
+            np.sqrt(dc1[eucl] ** 2 + dr1[eucl] ** 2),
+        )
+
+        if np.any(segment_dists > tolerance):
+            # select point with maximum distance to line
+            new_end = start + np.argmax(segment_dists) + 1
+            pos_stack.append((new_end, end))
+            pos_stack.append((start, new_end))
+            chain[new_end] = True
+
+        if len(pos_stack) == 0:
+            end_of_chain = True
+
+    return coords[chain, :]