1 files changed, 93 insertions, 0 deletions
diff --git a/scripts/check-no-white-blocks.py b/scripts/check-no-white-blocks.py
new file mode 100644
index 0000000..609c832
--- /dev/null
+++ b/scripts/check-no-white-blocks.py
@@ -0,0 +1,93 @@
+#!/usr/bin/env python3
+"""Fail if any recorded frame contains a near-white opaque block.
+
+This is the image-level regression guard for the P13/P14 lantern blow-out: a
+premultiplied-alpha mistake painted ~75x75 pure white (255,255,255) squares
+where the night lantern glow should fall off softly.
+
+A "white block" is any window of at least MIN_SIDE x MIN_SIDE pixels where every
+pixel is fully opaque (alpha >= 250) and every colour channel is >= 250.
+
+Usage:
+    python3 scripts/check-no-white-blocks.py <png-or-dir> [more...]
+
+Exit code 0 when clean, 1 when a block is found, 2 on usage/read error.
+"""
+
+import os
+import sys
+
+import numpy as np
+from PIL import Image
+
+MIN_SIDE = 64
+CHANNEL_MIN = 250
+ALPHA_MIN = 250
+
+
+def first_white_block(path, min_side=MIN_SIDE):
+    image = Image.open(path)
+    rgba = np.asarray(image.convert("RGBA"), dtype=np.uint8)
+    if rgba.shape[0] < min_side or rgba.shape[1] < min_side:
+        return None
+    white_opaque = (
+        (rgba[:, :, 0] >= CHANNEL_MIN)
+        & (rgba[:, :, 1] >= CHANNEL_MIN)
+        & (rgba[:, :, 2] >= CHANNEL_MIN)
+        & (rgba[:, :, 3] >= ALPHA_MIN)
+    ).astype(np.int64)
+    # Summed-area table so any k x k window is one lookup.
+    integral = np.zeros((white_opaque.shape[0] + 1, white_opaque.shape[1] + 1), dtype=np.int64)
+    integral[1:, 1:] = white_opaque.cumsum(0).cumsum(1)
+    rows, cols = white_opaque.shape
+    for y in range(0, rows - min_side + 1):
+        for x in range(0, cols - min_side + 1):
+            total = (
+                integral[y + min_side, x + min_side]
+                - integral[y, x + min_side]
+                - integral[y + min_side, x]
+                + integral[y, x]
+            )
+            if total == min_side * min_side:
+                return (x, y, min_side, min_side)
+    return None
+
+
+def iter_pngs(targets):
+    for target in targets:
+        if os.path.isdir(target):
+            for root, _, files in os.walk(target):
+                for name in sorted(files):
+                    if name.lower().endswith(".png"):
+                        yield os.path.join(root, name)
+        else:
+            yield target
+
+
+def main(argv):
+    if len(argv) < 2:
+        sys.stderr.write(__doc__)
+        return 2
+    checked = 0
+    failures = []
+    for path in iter_pngs(argv[1:]):
+        try:
+            block = first_white_block(path)
+        except Exception as error:  # noqa: BLE001 - report and continue
+            sys.stderr.write(f"unreadable: {path}: {error}\n")
+            return 2
+        checked += 1
+        if block is not None:
+            x, y, side, _ = block
+            failures.append(f"{path}: white block {side}x{side} at ({x},{y})")
+    for line in failures:
+        print(f"FAIL {line}")
+    if failures:
+        print(f"checked={checked} failures={len(failures)}")
+        return 1
+    print(f"checked={checked} failures=0 OK")
+    return 0
+
+
+if __name__ == "__main__":
+    raise SystemExit(main(sys.argv))