56 lines
1.8 KiB
TypeScript
56 lines
1.8 KiB
TypeScript
// Copyright 2020 Signal Messenger, LLC
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// SPDX-License-Identifier: AGPL-3.0-only
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import loadImage from 'blueimp-load-image';
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import { encode } from 'blurhash';
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type Input = Parameters<typeof loadImage>[0];
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const loadImageData = async (input: Input): Promise<ImageData> => {
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return new Promise((resolve, reject) => {
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loadImage(
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input,
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canvasOrError => {
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if (canvasOrError instanceof Event && canvasOrError.type === 'error') {
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const processError = new Error(
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'imageToBlurHash: Failed to process image'
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);
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processError.originalError = canvasOrError;
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reject(processError);
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return;
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}
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if (!(canvasOrError instanceof HTMLCanvasElement)) {
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reject(new Error('imageToBlurHash: result is not a canvas'));
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return;
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}
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const context = canvasOrError.getContext('2d');
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if (!context) {
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reject(
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new Error(
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'imageToBlurHash: cannot get CanvasRenderingContext2D from canvas'
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)
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);
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return;
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}
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resolve(
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context.getImageData(0, 0, canvasOrError.width, canvasOrError.height)
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);
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},
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// Calculating the blurhash on large images is a long-running and
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// synchronous operation, so here we ensure the images are a reasonable
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// size before calculating the blurhash. iOS uses a max size of 200x200
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// and Android uses a max size of 1/16 the original size. 200x200 is
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// easier for us.
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{ canvas: true, orientation: true, maxWidth: 200, maxHeight: 200 }
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);
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});
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};
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export const imageToBlurHash = async (input: Input): Promise<string> => {
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const { data, width, height } = await loadImageData(input);
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// 4 horizontal components and 3 vertical components
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return encode(data, width, height, 4, 3);
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};
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