Phase 10: sprite session — runner, brute, shield zombie, weapon tin

Sheets generated with the existing zombie sheet as the style anchor (edit mode);
sliced to z_f1/2 (runner sprint), z_g1/2 (brute + net-post club), z_s1/2/3
(shield zombie, chair up / chair dropped stagger), x_tin (black new-balls tin).
assets/_slice.py is now committed (chroma-key + de-fringe + segmentation) so the
pipeline survives scratchpad wipes; HANDOFF updated.

Sprites are NOT wired into render.js yet — Phase 11 does that after Oliver
approves the sheets (plan's design checkpoint).

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

assets/_slice.py

@@ -0,0 +1,71 @@
+# slice.py — chroma-key a generated sprite sheet on its corner color, split into
+# frames on column gaps, common-scale the sheet so the tallest frame = IDLE_TARGET_H,
+# save each frame to the given output paths. Usage: slice.py sheet.png out1.png out2.png ...
+import sys
+from PIL import Image
+
+IDLE_TARGET_H = 112
+KEY_D2 = 60 * 60   # squared RGB distance to the bg color that still counts as background
+MIN_GAP = 12       # empty columns that separate frames
+MIN_BLOB = 60      # despeckle: drop opaque islands smaller than this many pixels
+
+def main(sheet_path, out_paths, largest_only=False):
+    im = Image.open(sheet_path).convert('RGBA')
+    w, h = im.size
+    px = im.load()
+    # background = corner color (average the four corners that agree with the top-left)
+    bg = px[0, 0][:3]
+    for x in range(w):
+        for y in range(h):
+            r, g, b, a = px[x, y]
+            if (r - bg[0]) ** 2 + (g - bg[1]) ** 2 + (b - bg[2]) ** 2 < KEY_D2 \
+               or (min(r, b) > g + 40):  # de-fringe: magenta-hued halo pixels (sprites have no magenta)
+                px[x, y] = (0, 0, 0, 0)
+    # despeckle: flood-fill opaque components; wipe tiny ones (halos, dust).
+    # largest_only additionally wipes everything but the biggest blob (stray fragments
+    # from splitting a sheet whose frames touch — e.g. the brute's dragged pole).
+    seen = [[False] * h for _ in range(w)]
+    blobs = []
+    for x in range(w):
+        for y in range(h):
+            if seen[x][y] or px[x, y][3] == 0: continue
+            stack, blob = [(x, y)], []
+            seen[x][y] = True
+            while stack:
+                cx, cy = stack.pop()
+                blob.append((cx, cy))
+                for nx, ny in ((cx+1,cy),(cx-1,cy),(cx,cy+1),(cx,cy-1)):
+                    if 0 <= nx < w and 0 <= ny < h and not seen[nx][ny] and px[nx, ny][3] > 0:
+                        seen[nx][ny] = True; stack.append((nx, ny))
+            blobs.append(blob)
+    keep = max(blobs, key=len) if (largest_only and blobs) else None
+    for blob in blobs:
+        if blob is keep: continue
+        if largest_only or len(blob) < MIN_BLOB:
+            for cx, cy in blob: px[cx, cy] = (0, 0, 0, 0)
+    # segment on empty column runs
+    cols = [any(px[x, y][3] for y in range(h)) for x in range(w)]
+    frames, start, gap = [], None, 0
+    for x in range(w):
+        if cols[x]:
+            if start is None: start = x
+            gap = 0
+        elif start is not None:
+            gap += 1
+            if gap >= MIN_GAP:
+                frames.append((start, x - gap + 1)); start = None
+    if start is not None: frames.append((start, w))
+    crops = []
+    for x0, x1 in frames:
+        c = im.crop((x0, 0, x1, h))
+        crops.append(c.crop(c.getbbox()))
+    if len(crops) != len(out_paths):
+        sys.exit(f'ERROR: found {len(crops)} frames, expected {len(out_paths)} ({sheet_path})')
+    k = IDLE_TARGET_H / max(c.height for c in crops)  # one scale per sheet keeps relative frame sizes
+    for c, out in zip(crops, out_paths):
+        c.resize((max(1, round(c.width * k)), max(1, round(c.height * k))), Image.NEAREST).save(out)
+        print(f'{out}: {round(c.width * k)}x{round(c.height * k)}')
+
+if __name__ == '__main__':
+    args = [a for a in sys.argv[1:] if a != '--largest']
+    main(args[0], args[1:], largest_only='--largest' in sys.argv)