94 lines
2.9 KiB
Python
94 lines
2.9 KiB
Python
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# /// script
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# requires-python = ">=3.9"
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# dependencies = ["pillow"]
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# ///
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"""
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Generate routes/root/dist-strips.bin from routes/root/dist.png.
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Splits the 512x512 grayscale Julia distance field into N horizontal bands,
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re-encodes each band as its own WebP, and concatenates them in CENTER-OUT order
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(the band the pan/zoom animation shows first) so a streaming client can upload
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the visible region before the outer bands have finished downloading. WebP q90 is
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~half the size of PNG with no visible loss after the color-band mapping.
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File layout (little-endian):
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u32 headerLen
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bytes headerLen -- UTF-8 JSON: {fullW, fullH, bands:[{y,h,off,len}, ...]}
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bytes payload -- concatenated band WebPs in the order listed in `bands`
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(off/len are byte ranges within payload, stream order)
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Re-run only when dist.png changes; the output is committed.
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Usage: uv run tools/gen-strips.py
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"""
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import io
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import json
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import os
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import struct
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from PIL import Image
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HERE = os.path.dirname(os.path.abspath(__file__))
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ROOT = os.path.dirname(HERE)
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SRC = os.path.join(ROOT, "routes", "root", "dist.png")
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OUT = os.path.join(ROOT, "routes", "root", "dist-strips.bin")
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NBANDS = 8
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WEBP_QUALITY = 90 # lossy; ~half of PNG, visually identical. Bump to 95 / use lossless if needed.
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def center_out(n):
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"""Band indices ordered from the middle outward: e.g. n=8 -> [4,3,5,2,6,1,7,0]."""
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order = []
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lo, hi = n // 2 - 1, n // 2
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while lo >= 0 or hi < n:
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if hi < n:
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order.append(hi)
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hi += 1
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if lo >= 0:
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order.append(lo)
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lo -= 1
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return order
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def main():
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img = Image.open(SRC).convert("L")
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w, h = img.size
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# Row boundaries (robust if h is not divisible by NBANDS).
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bounds = [round(i * h / NBANDS) for i in range(NBANDS + 1)]
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bands_by_index = []
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for i in range(NBANDS):
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y0, y1 = bounds[i], bounds[i + 1]
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crop = img.crop((0, y0, w, y1))
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buf = io.BytesIO()
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crop.save(buf, format="WEBP", quality=WEBP_QUALITY, method=6)
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bands_by_index.append((y0, y1 - y0, buf.getvalue()))
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payload = bytearray()
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meta = []
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order = center_out(NBANDS)
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for idx in order:
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y, bh, png = bands_by_index[idx]
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meta.append({"y": y, "h": bh, "off": len(payload), "len": len(png)})
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payload += png
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header = json.dumps(
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{"fullW": w, "fullH": h, "bands": meta}, separators=(",", ":")
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).encode("utf-8")
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with open(OUT, "wb") as f:
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f.write(struct.pack("<I", len(header)))
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f.write(header)
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f.write(payload)
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total = 4 + len(header) + len(payload)
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src_size = os.path.getsize(SRC)
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print(f"{w}x{h} -> {NBANDS} bands, center-out order {order}")
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print(
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f"header {len(header)}B, payload {len(payload)}B, total {total}B "
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f"({total / 1024:.1f} KB) vs dist.png {src_size}B ({src_size / 1024:.1f} KB)"
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)
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print(f"wrote {OUT}")
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if __name__ == "__main__":
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main()
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