Refine freehand exclusion polygons

Store freehand paths as closed polygons with thin outlines and fill the interior when masking, so free-drawn shapes behave like custom rectangles.

app/gui/exclusions.py

@@ -14,7 +14,6 @@ class ExclusionMixin:
         y = max(0, min(self.preview_img.height - 1, int(event.y)))
         if mode == "free":
             self._current_stroke = [(x, y)]
-            width = int(getattr(self, "free_draw_width", 14))
             preview_id = getattr(self, "_stroke_preview_id", None)
             if preview_id:
                 try:
@@ -27,15 +26,13 @@ class ExclusionMixin:
                 x,
                 y,
                 fill="yellow",
-                width=width,
+                width=2,
                 smooth=True,
                 capstyle="round",
                 joinstyle="round",
             )
             self._rubber_start = None
             return
-        x = max(0, min(self.preview_img.width - 1, int(event.x)))
-        y = max(0, min(self.preview_img.height - 1, int(event.y)))
         self._rubber_start = (x, y)
         if self._rubber_id:
             try:
@@ -70,13 +67,12 @@ class ExclusionMixin:
         mode = getattr(self, "exclude_mode", "rect")
         if mode == "free":
             stroke = getattr(self, "_current_stroke", None)
-            if stroke and len(stroke) > 1:
-                cleaned = self._compress_stroke(stroke)
-                if len(cleaned) > 1:
+            if stroke and len(stroke) > 2:
+                polygon = self._close_polygon(self._compress_stroke(stroke))
+                if len(polygon) >= 3:
                     shape = {
-                        "kind": "stroke",
-                        "points": cleaned,
-                        "width": int(getattr(self, "free_draw_width", 14)),
+                        "kind": "polygon",
+                        "points": polygon,
                     }
                     self.exclude_shapes.append(shape)
                     stamper = getattr(self, "_stamp_shape_on_mask", None)
@@ -190,5 +186,15 @@ class ExclusionMixin:
                 compressed.append(point)
         return compressed
 
+    @staticmethod
+    def _close_polygon(points: list[tuple[int, int]]) -> list[tuple[int, int]]:
+        """Ensure the polygon is closed by repeating the start if necessary."""
+        if len(points) < 3:
+            return points
+        closed = list(points)
+        if closed[0] != closed[-1]:
+            closed.append(closed[0])
+        return closed
+
 
 __all__ = ["ExclusionMixin"]