103 lines
2.8 KiB
JavaScript
103 lines
2.8 KiB
JavaScript
// @ts-check
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import { GifNodeType } from "./constants.js";
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/** @typedef {import("../../types/gif.d.ts").GifNode} GifNode */
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/**
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* @typedef {object} LogicalScreenDescriptorPackedField
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* @prop {boolean} globalColorTableFlag
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* @prop {number} colorResolution
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* @prop {boolean} sortFlag
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* @prop {number} sizeOfGlobalColorTable
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*/
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/**
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* @param {number} byte
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* @returns {LogicalScreenDescriptorPackedField}
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*/
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export const parseLogicalScreenDescriptorPackedField = (byte) => ({
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globalColorTableFlag: (byte & 0b10000000) !== 0,
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colorResolution: ((byte & 0b01110000) >> 4) + 1,
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sortFlag: (byte & 0b00001000) !== 0,
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sizeOfGlobalColorTable: 2 ** ((byte & 0b00000111) + 1),
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});
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/**
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* @param {Uint8Array} bytes
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* @returns {null | GifNode} The root node of the GIF tree, or null if the GIF is invalid.
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*/
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export default (bytes) => {
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const widthBytes = bytes.subarray(6, 6 + 2);
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const heightBytes = bytes.subarray(8, 8 + 2);
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const packedFieldBytes = bytes.subarray(10, 10 + 1);
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/** @type {GifNode[]} */
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const children = [
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{
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type: GifNodeType.header,
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bytes: bytes.subarray(0, 6),
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children: [
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{
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type: GifNodeType.headerSignature,
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bytes: bytes.subarray(0, 3),
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},
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{
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type: GifNodeType.headerVersion,
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bytes: bytes.subarray(3, 3 + 3),
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},
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],
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},
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{
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type: GifNodeType.logicalScreenDescriptor,
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bytes: bytes.subarray(6, 6 + 6),
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children: [
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{
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type: GifNodeType.logicalScreenWidth,
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bytes: widthBytes,
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},
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{
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type: GifNodeType.logicalScreenHeight,
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bytes: heightBytes,
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},
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{
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type: GifNodeType.logicalScreenDescriptorPackedFields,
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bytes: packedFieldBytes,
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},
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{
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type: GifNodeType.logicalScreenBackgroundColorIndex,
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bytes: bytes.subarray(11, 11 + 1),
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},
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{
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type: GifNodeType.logicalScreenPixelAspectRatio,
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bytes: bytes.subarray(12, 12 + 1),
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},
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],
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},
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];
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let offset = 13;
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const packedField = parseLogicalScreenDescriptorPackedField(
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packedFieldBytes[0],
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);
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if (packedField.globalColorTableFlag) {
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/** @type {GifNode[]} */ const colorNodes = [];
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for (let i = 0; i < packedField.sizeOfGlobalColorTable; i++) {
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colorNodes.push({
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type: GifNodeType.globalColorTableColor,
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bytes: bytes.subarray(13 + (i * 3), 13 + (i * 3) + 3),
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});
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}
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const sizeOfGlobalColorTableInBytes = packedField.sizeOfGlobalColorTable *
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3;
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children.push({
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type: GifNodeType.globalColorTable,
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bytes: bytes.subarray(13, 13 + sizeOfGlobalColorTableInBytes),
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children: colorNodes,
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});
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offset += sizeOfGlobalColorTableInBytes;
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}
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return { type: GifNodeType.root, bytes, children };
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};
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