Ignore negative seed coordinates in floodfill

Tests/test_imagedraw.py

@@ -991,6 +991,14 @@ def test_floodfill(bbox: Coords) -> None:
     assert_image_equal(im, Image.new("RGB", (1, 1), red))
 
 
+@pytest.mark.parametrize("xy", ((-1, 1), (1, -1), (-1, -1), (-3, 0), (0, -3)))
+def test_floodfill_negative_seed(xy: tuple[int, int]) -> None:
+    im = Image.new("RGB", (3, 3))
+    original = im.copy()
+    ImageDraw.floodfill(im, xy, (255, 0, 0))
+    assert_image_equal(im, original)
+
+
 @pytest.mark.parametrize("bbox", BBOX)
 def test_floodfill_border(bbox: Coords) -> None:
     # floodfill() is experimental

docs/releasenotes/13.1.0.rst

@@ -49,6 +49,12 @@ TODO
 Other changes
 =============
 
+Negative seed coordinates in ImageDraw.floodfill
+^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+
+:py:func:`~PIL.ImageDraw.floodfill` now leaves the image unchanged when either
+seed coordinate is negative, instead of wrapping around to the opposite edge.
+
 Resizing I;16B and I;16N images
 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
 

src/PIL/ImageDraw.py

@@ -830,6 +830,8 @@ def floodfill(
     pixel = image.load()
     assert pixel is not None
     x, y = xy
+    if x < 0 or y < 0:
+        return
     try:
         background = pixel[x, y]
         if _color_diff(value, background) <= thresh: