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#!/usr/bin/env -S uv run --script
# /// script
# requires-python = ">=3.10"
# dependencies = []
# ///
from __future__ import annotations
import math
import struct
import sys
import zlib
from pathlib import Path
PIXELS_PER_BAYER_CELL = 16
TOTAL_DOT_AREA = 0.5
SDF_RADIUS_SCALE = 2.4
BINARY_THRESHOLD = 2.0 / 3.0
BASE_BAYER_POINTS = (
(0.0, 0.0),
(0.5, 0.5),
(0.5, 0.0),
(0.0, 0.5),
)
def main(argv: list[str]) -> int:
if len(argv) != 2:
print(f"usage: {Path(argv[0]).name} N", file=sys.stderr)
return 2
try:
order = int(argv[1])
except ValueError:
print("N must be an integer.", file=sys.stderr)
return 2
if order < 1 or order & (order - 1):
print("N must be a positive power of two.", file=sys.stderr)
return 2
output_dir = Path.cwd() / f"SSFD_{order}x{order}"
output_dir.mkdir(parents=True, exist_ok=True)
clear_previous_outputs(output_dir)
size = order * PIXELS_PER_BAYER_CELL
points = build_bayer_points(order)
min_dist_sq = [math.inf] * (size * size)
sample_x = [((x + 0.5) / size) for x in range(size)]
sample_y = [((y + 0.5) / size) for y in range(size)]
for layer_index, point in enumerate(points, start=1):
update_min_distances(min_dist_sq, sample_x, sample_y, size, point)
write_layer(output_dir, min_dist_sq, size, layer_index)
print(f"Wrote {len(points)} textures to {output_dir}")
return 0
def clear_previous_outputs(output_dir: Path) -> None:
for pattern in (
"dots_L*.png",
"dots_L*-sdf.png",
"dots_L*.png.meta",
"dots_L*-sdf.png.meta",
):
for path in output_dir.glob(pattern):
if path.is_file():
path.unlink()
def build_bayer_points(order: int) -> list[tuple[float, float]]:
if order == 1:
return [(0.0, 0.0)]
recursion = int(math.log2(order))
points = list(BASE_BAYER_POINTS)
for r in range(recursion - 1):
count = len(points)
offset = 0.5 ** (r + 1)
for i in range(1, 4):
dx, dy = BASE_BAYER_POINTS[i]
for j in range(count):
px, py = points[j]
points.append((px + dx * offset, py + dy * offset))
return points
def update_min_distances(
min_dist_sq: list[float],
sample_x: list[float],
sample_y: list[float],
size: int,
point: tuple[float, float],
) -> None:
px, py = point
for y, sy in enumerate(sample_y):
dy = wrap_delta(sy - py)
dy_sq = dy * dy
row_offset = y * size
for x, sx in enumerate(sample_x):
dx = wrap_delta(sx - px)
dist_sq = dx * dx + dy_sq
idx = row_offset + x
if dist_sq < min_dist_sq[idx]:
min_dist_sq[idx] = dist_sq
def write_layer(output_dir: Path, min_dist_sq: list[float], size: int, layer_index: int) -> None:
dot_radius = math.sqrt((TOTAL_DOT_AREA / layer_index) / math.pi)
scale = dot_radius * SDF_RADIUS_SCALE
sdf_pixels = bytearray()
binary_pixels = bytearray()
for dist_sq in min_dist_sq:
dist = math.sqrt(dist_sq)
value = clamp01(1.0 - dist / scale)
sdf_byte = round(value * 255.0)
sdf_pixels.append(sdf_byte)
binary_pixels.append(255 if value >= BINARY_THRESHOLD else 0)
write_grayscale_png(output_dir / f"dots_L{layer_index}-sdf.png", size, size, sdf_pixels)
write_grayscale_png(output_dir / f"dots_L{layer_index}.png", size, size, binary_pixels)
def wrap_delta(value: float) -> float:
return (value + 0.5) % 1.0 - 0.5
def clamp01(value: float) -> float:
if value <= 0.0:
return 0.0
if value >= 1.0:
return 1.0
return value
def write_grayscale_png(path: Path, width: int, height: int, pixels: bytearray) -> None:
raw = bytearray()
stride = width
for y in range(height):
start = y * stride
raw.append(0)
raw.extend(pixels[start : start + stride])
compressed = zlib.compress(bytes(raw), level=9)
with path.open("wb") as handle:
handle.write(b"\x89PNG\r\n\x1a\n")
handle.write(make_chunk(b"IHDR", struct.pack(">IIBBBBB", width, height, 8, 0, 0, 0, 0)))
handle.write(make_chunk(b"IDAT", compressed))
handle.write(make_chunk(b"IEND", b""))
def make_chunk(chunk_type: bytes, payload: bytes) -> bytes:
return (
struct.pack(">I", len(payload))
+ chunk_type
+ payload
+ struct.pack(">I", zlib.crc32(chunk_type + payload) & 0xFFFFFFFF)
)
if __name__ == "__main__":
raise SystemExit(main(sys.argv))
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