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import { calcIndex } from "./_common.ts";
export function createDecoder(): (
input: Uint8Array,
i: number,
o: number,
) => { i: number; o: number; c: number; isEnd: boolean } {
const previousPixel = new Uint8Array([0, 0, 0, 255]);
const seenPixels: Uint8Array[] = new Array(64)
.fill(0)
.map((_) => new Uint8Array([0, 0, 0, 0]));
return function (
data: Uint8Array,
i: number,
o: number,
): { i: number; o: number; c: number; isEnd: boolean } {
let c = 0;
for (; i <= data.length - 8; o += 4) {
if ([0, 0, 0, 0, 0, 0, 0, 1].every((x, j) => x === data[i + j])) {
return { i, o, c, isEnd: true };
}
++c;
if (data[i] === 0b11111111) {
// QOI_OP_RGBA
previousPixel.set(data.subarray(i + 1, i + 5));
seenPixels[calcIndex(previousPixel, false)].set(previousPixel);
data.set(previousPixel, o);
i += 5;
} else if (data[i] === 0b11111110) {
// QOI_OP_RGB
previousPixel.set(data.subarray(i + 1, i + 4));
previousPixel[3] = 255;
seenPixels[calcIndex(previousPixel, true)].set(previousPixel);
data.set(previousPixel, o);
i += 4;
} else {
switch (data[i] >> 6) {
case 0:
// QOI_OP_INDEX
previousPixel.set(seenPixels[data[i++] & 0b00111111]);
data.set(previousPixel, o);
break;
case 1:
// QOI_OP_DIFF
previousPixel[0] += (data[i] >> 4 & 0b11) - 2;
previousPixel[1] += (data[i] >> 2 & 0b11) - 2;
previousPixel[2] += (data[i++] & 0b11) - 2;
seenPixels[calcIndex(previousPixel, false)].set(previousPixel);
data.set(previousPixel, o);
break;
case 2: {
// QOI_OP_LUMA
const greenDiff = (data[i] & 0b00111111) - 32;
previousPixel[0] += (data[++i] >> 4) + greenDiff - 8;
previousPixel[1] += greenDiff;
previousPixel[2] += (data[i++] & 0b00001111) + greenDiff - 8;
seenPixels[calcIndex(previousPixel, false)].set(previousPixel);
data.set(previousPixel, o);
break;
}
default: { // 3
// QOI_OP_RUN
const run = data[i++] & 0b00111111;
c += run;
for (let j = 0; j < run; ++j) {
data.set(previousPixel, o);
o += 4;
}
data.set(previousPixel, o);
}
}
}
}
return { i, o, c, isEnd: false };
};
}
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