Fallback points for bounding boxes

arcade/hitbox/base.py

@@ -67,6 +67,24 @@ def __call__(self, *args: Any, **kwds: Any) -> Self:
         """
         return self.__class__(*args, **kwds)  # type: ignore
 
+    def create_bounding_box(self, image: Image) -> PointList:
+        """
+        Create points for a simple bounding box around an image.
+        This is often used as a fallback if a hit box algorithm
+        doesn't manage to figure out any reasonable points for
+        an image.
+
+        :param Image image: The image to create a bounding box for.
+        :return: A tuple of hit box points.
+        """
+        size = image.size
+        return (
+            (-size[0] / 2, -size[1] / 2),
+            (size[0] / 2, -size[1] / 2),
+            (size[0] / 2, size[1] / 2),
+            (-size[0] / 2, size[1] / 2),
+        )
+
 
 class HitBox:
     """

arcade/hitbox/bounding_box.py

@@ -20,10 +20,4 @@ def calculate(self, image: Image, **kwargs) -> PointList:
 
         :Returns: List of points
         """
-        size = image.size
-        return (
-            (-size[0] / 2, -size[1] / 2),
-            (size[0] / 2, -size[1] / 2),
-            (size[0] / 2, size[1] / 2),
-            (-size[0] / 2, size[1] / 2),
-        )
+        return self.create_bounding_box(image)

arcade/hitbox/pymunk.py

@@ -51,7 +51,7 @@ def calculate(self, image: Image, detail: Optional[float] = None, **kwargs) -> P
         # Trace the image finding all the outlines and holes
         line_sets = self.trace_image(image)
         if len(line_sets) == 0:
-            return tuple()
+            return self.create_bounding_box(image)
 
         # Get the largest line set
         line_set = self.select_largest_line_set(line_sets)

arcade/hitbox/simple.py

@@ -29,7 +29,7 @@ def calculate(self, image: Image, **kwargs) -> PointList:
         bbox = image.getbbox()
         # If there is no bounding box the image is empty
         if bbox is None:
-            return tuple()
+            return self.create_bounding_box(image)
 
         left_border, top_border, right_border, bottom_border = bbox
         right_border -= 1

tests/unit/htibox/test_black_image.py

@@ -0,0 +1,23 @@
+"""
+Test fallback for hitbox creation with empty textures.
+"""
+from PIL import Image
+import arcade
+
+EXPECTED = ((-50.0, -50.0), (50.0, -50.0), (50.0, 50.0), (-50.0, 50.0))
+
+
+def test_simple():
+    tex = arcade.Texture(
+        Image.new("RGBA", (100, 100)),
+        hit_box_algorithm=arcade.hitbox.algo_simple,
+    )
+    assert tex.hit_box_points == EXPECTED
+
+
+def test_pymunk():
+    tex = arcade.Texture(
+        Image.new("RGBA", (100, 100)),
+        hit_box_algorithm=arcade.hitbox.algo_detailed,
+    )
+    assert tex.hit_box_points == EXPECTED