Add a frames-to-GIF tool for animation exports

tools/frames_to_gif.py

@@ -0,0 +1,62 @@
+"""Merge a folder of numbered PNG frames into an animated GIF.
+
+The inverse of extract_card_frames/extract_flame_frames: point it at a
+directory of frames (000.png, 001.png, ...) from a game animation export and
+it produces one GIF, transparency preserved. Needs ffmpeg on PATH (the
+palettegen/paletteuse pass is what keeps sprite alpha and colors clean).
+
+Usage:
+  python tools/frames_to_gif.py <frames_dir> [-o out.gif] [--fps 15] [--width N]
+"""
+
+from __future__ import annotations
+
+import argparse
+import subprocess
+import sys
+from pathlib import Path
+
+
+def main() -> None:
+    parser = argparse.ArgumentParser()
+    parser.add_argument("frames_dir", type=Path)
+    parser.add_argument("-o", "--output", type=Path, default=None)
+    parser.add_argument("--fps", type=int, default=15)
+    parser.add_argument("--width", type=int, default=None, help="scale to this width")
+    args = parser.parse_args()
+
+    frames = sorted(args.frames_dir.glob("*.png"))
+    if not frames:
+        sys.exit(f"no .png frames in {args.frames_dir}")
+    out = args.output or args.frames_dir.with_suffix(".gif")
+
+    scale = f"scale={args.width}:-1:flags=lanczos," if args.width else ""
+    filters = (
+        f"{scale}split[s0][s1];"
+        "[s0]palettegen=reserve_transparent=1[p];"
+        "[s1][p]paletteuse=alpha_threshold=128"
+    )
+    cmd = [
+        "ffmpeg",
+        "-y",
+        "-loglevel",
+        "error",
+        "-framerate",
+        str(args.fps),
+        "-pattern_type",
+        "glob",
+        "-i",
+        str(args.frames_dir / "*.png"),
+        "-lavfi",
+        filters,
+        "-gifflags",
+        "+transdiff",
+        str(out),
+    ]
+    subprocess.run(cmd, check=True)
+    size = out.stat().st_size
+    print(f"{out}: {len(frames)} frames @ {args.fps}fps, {size / 1024:.0f} KB")
+
+
+if __name__ == "__main__":
+    main()