feat(selection): separate selection geometry from image content processing

- Introduced a new design for selection rasterization that decouples the selection geometry from the image content, ensuring that the SelectionMask is independent of the source image's alpha and color.
- Updated the `rasterize_selection_path` function to only accept selection paths and image dimensions, removing parameters related to source alpha and alpha thresholds.
- Implemented a new approach for handling selection paths using non-zero winding fill, ensuring overlapping areas are preserved.
- Enhanced performance by utilizing a scanline algorithm for rasterization, significantly reducing processing time for high-resolution images.
- Updated internal documentation and added comprehensive tests to validate the new behavior and performance improvements.
- Ensured backward compatibility by maintaining existing interfaces where necessary while introducing breaking changes in the selection processing logic.

src/anyimage/common/viewport.py

@@ -326,12 +326,10 @@ def triangulated_polygon_vertices(vertices):
         return _triangulated_polygon_vertices_python(vertices)
 
 
-def scanline_fill_triangles(vertices, fill_rule="EVEN_ODD", step=2.0):
+def scanline_fill_triangles(vertices, step=2.0):
     vertices = tuple(tuple(float(value) for value in vertex) for vertex in vertices)
     if len(vertices) < 3:
         return ()
-    if fill_rule not in {"EVEN_ODD", "NONZERO"}:
-        raise ValueError(f"Unknown polygon fill rule: {fill_rule}")
     minimum_y = min(vertex[1] for vertex in vertices)
     maximum_y = max(vertex[1] for vertex in vertices)
     band_bottom = minimum_y
@@ -358,17 +356,11 @@ def scanline_fill_triangles(vertices, fill_rule="EVEN_ODD", step=2.0):
         while index < len(events):
             x = events[index][0]
             delta = 0
-            count = 0
             while index < len(events) and abs(events[index][0] - x) <= 1e-8:
                 delta += events[index][1]
-                count += 1
                 index += 1
             was_inside = winding != 0
-            if fill_rule == "EVEN_ODD":
-                if count % 2:
-                    winding = 0 if was_inside else 1
-            else:
-                winding += delta
+            winding += delta
             is_inside = winding != 0
             if not was_inside and is_inside:
                 interval_start = x
@@ -454,12 +446,12 @@ def polygon_self_intersects(vertices, cell_size=32.0):
     return False
 
 
-def preview_fill_triangles(vertices, fill_rule="EVEN_ODD"):
+def preview_fill_triangles(vertices):
     if not polygon_self_intersects(vertices):
         triangles = triangulated_polygon_vertices(vertices)
         if triangles:
             return triangles
-    return scanline_fill_triangles(vertices, fill_rule)
+    return scanline_fill_triangles(vertices)
 
 
 def draw_polygon_fill(
@@ -609,7 +601,6 @@ def image_line_half_plane_polygon(line, image_size):
 
 class ImageSelectionGesture:
     active_tool_id = None
-    preview_fill_rule = "EVEN_ODD"
     _path = None
     _cursor = None
     _handle = None
@@ -658,9 +649,7 @@ class ImageSelectionGesture:
         if len(polygon) >= 3:
             if polygon != self._fill_polygon:
                 self._fill_polygon = polygon
-                self._fill_triangles = preview_fill_triangles(
-                    polygon, self.preview_fill_rule
-                )
+                self._fill_triangles = preview_fill_triangles(polygon)
             draw_polygon_fill(
                 polygon,
                 self._fill_triangles,
@@ -725,6 +714,9 @@ class ImageSelectionGesture:
     def cancel(self, context):
         self._finish(context)
 
+    def _submit_selection_path(self, _context, _selection_path):
+        raise NotImplementedError
+
     def invoke(self, context, event):
         source_object, should_edit = resolve_image_edit_click(
             context, event, self.report
@@ -740,7 +732,6 @@ class ImageSelectionGesture:
         self.invert = False
         self.source_object_name = source_object.name
         self.source_matrix_data = serialize_matrix(source_object.matrix_world)
-        self.selection_path_json = ""
         point = (float(event.mouse_region_x), float(event.mouse_region_y))
         self._path = [point]
         self._cursor = point
@@ -787,13 +778,12 @@ class ImageSelectionGesture:
                 image_empty_bounds(source_object),
                 tuple(source_object.data.size),
             )
-        self.selection_path_json = SelectionPath(
+        selection_path = SelectionPath(
             points=selection_path,
             invert=self.invert,
-            fill_rule=self.preview_fill_rule,
-        ).to_json()
+        )
         self._finish(context)
-        return self.execute(context)
+        return self._submit_selection_path(context, selection_path)
 
     def modal(self, context, event):
         active_tool = active_view3d_tool_id(context)