Fix #140556: Mask filter operations behave incorrectly on dense meshes

Mistake in 57c4e9dd2c

Pull Request: https://projects.blender.org/blender/blender/pulls/140570

tests/python/CMakeLists.txt

@@ -1263,6 +1263,13 @@ if(TEST_SRC_DIR_EXISTS)
     --
     --testdir "${TEST_SRC_DIR}/sculpting"
   )
+
+  add_blender_test(
+    bl_sculpt_mask_filter
+    --python ${CMAKE_CURRENT_LIST_DIR}/sculpt_paint/mask_filter_test.py
+    --
+    --testdir "${TEST_SRC_DIR}/sculpting"
+  )
 endif()
 
 if(WITH_GPU_MESH_PAINT_TESTS AND TEST_SRC_DIR_EXISTS)

tests/python/sculpt_paint/mask_filter_test.py

@@ -0,0 +1,85 @@
+# SPDX-FileCopyrightText: 2025 Blender Authors
+#
+# SPDX-License-Identifier: GPL-2.0-or-later */
+
+__all__ = (
+    "main",
+)
+
+import math
+import unittest
+import sys
+import pathlib
+import numpy as np
+
+import bpy
+
+"""
+blender -b --factory-startup --python tests/python/sculpt_paint/mask_filter_test.py -- --testdir tests/files/sculpting/
+"""
+
+args = None
+
+
+class GrowMaskTest(unittest.TestCase):
+    def setUp(self):
+        bpy.ops.wm.open_mainfile(filepath=str(args.testdir / "partially_masked_sphere.blend"), load_ui=False)
+        bpy.ops.ed.undo_push()
+
+    def test_grow_increases_number_of_masked_vertices(self):
+        mesh = bpy.context.object.data
+        mask_attr = mesh.attributes['.sculpt_mask']
+
+        num_vertices = mesh.attributes.domain_size('POINT')
+
+        old_mask_data = np.zeros(num_vertices, dtype=np.float32)
+        mask_attr.data.foreach_get('value', old_mask_data)
+
+        bpy.ops.sculpt.mask_filter(filter_type='GROW')
+
+        new_mask_data = np.zeros(num_vertices, dtype=np.float32)
+        mask_attr.data.foreach_get('value', new_mask_data)
+
+        self.assertGreater(np.count_nonzero(new_mask_data), np.count_nonzero(old_mask_data))
+
+
+class ShrinkMaskTest(unittest.TestCase):
+    def setUp(self):
+        bpy.ops.wm.open_mainfile(filepath=str(args.testdir / "partially_masked_sphere.blend"), load_ui=False)
+        bpy.ops.ed.undo_push()
+
+    def test_shrink_decreases_number_of_masked_vertices(self):
+        mesh = bpy.context.object.data
+        mask_attr = mesh.attributes['.sculpt_mask']
+
+        num_vertices = mesh.attributes.domain_size('POINT')
+
+        old_mask_data = np.zeros(num_vertices, dtype=np.float32)
+        mask_attr.data.foreach_get('value', old_mask_data)
+
+        bpy.ops.sculpt.mask_filter(filter_type='SHRINK')
+
+        new_mask_data = np.zeros(num_vertices, dtype=np.float32)
+        mask_attr.data.foreach_get('value', new_mask_data)
+
+        self.assertLess(np.count_nonzero(new_mask_data), np.count_nonzero(old_mask_data))
+
+
+def main():
+    global args
+    import argparse
+
+    argv = [sys.argv[0]]
+    if '--' in sys.argv:
+        argv += sys.argv[sys.argv.index('--') + 1:]
+
+    parser = argparse.ArgumentParser()
+    parser.add_argument('--testdir', required=True, type=pathlib.Path)
+
+    args, remaining = parser.parse_known_args(argv)
+
+    unittest.main(argv=remaining)
+
+
+if __name__ == "__main__":
+    main()