57 lines
2.1 KiB
JavaScript
57 lines
2.1 KiB
JavaScript
import { unfilterAverage, unfilterNone, unfilterPaeth, unfilterSub, unfilterUp, } from './unfilter';
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const uint16 = new Uint16Array([0x00ff]);
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const uint8 = new Uint8Array(uint16.buffer);
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const osIsLittleEndian = uint8[0] === 0xff;
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const empty = new Uint8Array(0);
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export function decodeInterlaceNull(params) {
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const { data, width, height, channels, depth } = params;
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const bytesPerPixel = Math.ceil(depth / 8) * channels;
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const bytesPerLine = Math.ceil((depth / 8) * channels * width);
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const newData = new Uint8Array(height * bytesPerLine);
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let prevLine = empty;
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let offset = 0;
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let currentLine;
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let newLine;
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for (let i = 0; i < height; i++) {
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currentLine = data.subarray(offset + 1, offset + 1 + bytesPerLine);
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newLine = newData.subarray(i * bytesPerLine, (i + 1) * bytesPerLine);
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switch (data[offset]) {
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case 0:
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unfilterNone(currentLine, newLine, bytesPerLine);
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break;
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case 1:
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unfilterSub(currentLine, newLine, bytesPerLine, bytesPerPixel);
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break;
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case 2:
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unfilterUp(currentLine, newLine, prevLine, bytesPerLine);
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break;
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case 3:
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unfilterAverage(currentLine, newLine, prevLine, bytesPerLine, bytesPerPixel);
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break;
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case 4:
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unfilterPaeth(currentLine, newLine, prevLine, bytesPerLine, bytesPerPixel);
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break;
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default:
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throw new Error(`Unsupported filter: ${data[offset]}`);
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}
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prevLine = newLine;
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offset += bytesPerLine + 1;
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}
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if (depth === 16) {
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const uint16Data = new Uint16Array(newData.buffer);
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if (osIsLittleEndian) {
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for (let k = 0; k < uint16Data.length; k++) {
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// PNG is always big endian. Swap the bytes.
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uint16Data[k] = swap16(uint16Data[k]);
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}
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}
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return uint16Data;
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}
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else {
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return newData;
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}
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}
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function swap16(val) {
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return ((val & 0xff) << 8) | ((val >> 8) & 0xff);
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}
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//# sourceMappingURL=decodeInterlaceNull.js.map
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