Add explosion stage 1 PNG assets for all directions

- Added BMP_1_EXPLOSION_DOWN.png to original and preview directories.
- Added BMP_1_EXPLOSION_LEFT.png to original and preview directories.
- Added BMP_1_EXPLOSION_RIGHT.png to original and preview directories.
- Added BMP_1_EXPLOSION_UP.png to original and preview directories.

These assets are part of the explosion animation for the game, enhancing visual effects during gameplay.

tools/vernon/enhance_stage1_explosions.py

@@ -0,0 +1,74 @@
+#!/usr/bin/env python3
+import json
+import sys
+from pathlib import Path
+
+from PIL import Image
+
+
+CHROMAKEY = [128, 128, 128, 255]
+GREEN_LIGHT = [0, 255, 0, 255]
+GREEN_DARK = [0, 128, 0, 255]
+
+
+def is_green(pixel):
+    return pixel == GREEN_LIGHT or pixel == GREEN_DARK
+
+
+def is_background(pixel):
+    return pixel == CHROMAKEY or is_green(pixel)
+
+
+def cave_reference_path(sprite_name):
+    direction = sprite_name.rsplit("_", 1)[-1]
+    return Path("assets/Rat") / f"BMP_1_CAVE_{direction}.png"
+
+
+def load_cave_grid(sprite_name):
+    cave_path = cave_reference_path(sprite_name)
+    cave_image = Image.open(cave_path).convert("RGBA")
+    width, height = cave_image.size
+    pixel_access = cave_image.load()
+    return [
+        [list(pixel_access[x, y]) for x in range(width)]
+        for y in range(height)
+    ]
+
+
+def enhance_pixels(name, pixels):
+    cave_pixels = load_cave_grid(name)
+    enhanced = []
+    for y, row in enumerate(pixels):
+        enhanced_row = []
+        for x, pixel in enumerate(row):
+            if is_background(pixel):
+                enhanced_row.append(cave_pixels[y][x][:])
+            else:
+                enhanced_row.append(pixel[:])
+        enhanced.append(enhanced_row)
+    return enhanced
+
+
+def process_file(src_path, dst_path):
+    data = json.loads(src_path.read_text())
+    pixels = data["pixels"]
+    data["pixels"] = enhance_pixels(src_path.stem, pixels)
+    dst_path.write_text(json.dumps(data, indent=2))
+
+
+def main():
+    if len(sys.argv) != 3:
+        raise SystemExit("usage: enhance_stage1_explosions.py <src_dir> <dst_dir>")
+
+    src_dir = Path(sys.argv[1])
+    dst_dir = Path(sys.argv[2])
+    dst_dir.mkdir(parents=True, exist_ok=True)
+
+    for src_path in sorted(src_dir.glob("BMP_1_EXPLOSION_*.json")):
+        dst_path = dst_dir / src_path.name
+        process_file(src_path, dst_path)
+        print(f"Wrote {dst_path}")
+
+
+if __name__ == "__main__":
+    main()