mirror of https://github.com/CesiumGS/cesium.git
45 lines
1.5 KiB
JavaScript
45 lines
1.5 KiB
JavaScript
import defined from "./defined.js";
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const context2DsByWidthAndHeight = {};
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/**
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* Extract a pixel array from a loaded image. Draws the image
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* into a canvas so it can read the pixels back.
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*
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* @function getImagePixels
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*
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* @param {HTMLImageElement|ImageBitmap} image The image to extract pixels from.
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* @param {number} width The width of the image. If not defined, then image.width is assigned.
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* @param {number} height The height of the image. If not defined, then image.height is assigned.
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* @returns {ImageData} The pixels of the image.
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*/
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function getImagePixels(image, width, height) {
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if (!defined(width)) {
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width = image.width;
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}
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if (!defined(height)) {
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height = image.height;
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}
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let context2DsByHeight = context2DsByWidthAndHeight[width];
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if (!defined(context2DsByHeight)) {
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context2DsByHeight = {};
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context2DsByWidthAndHeight[width] = context2DsByHeight;
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}
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let context2d = context2DsByHeight[height];
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if (!defined(context2d)) {
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const canvas = document.createElement("canvas");
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canvas.width = width;
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canvas.height = height;
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// Since we re-use contexts, use the willReadFrequently option – See https://html.spec.whatwg.org/multipage/canvas.html#concept-canvas-will-read-frequently
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context2d = canvas.getContext("2d", { willReadFrequently: true });
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context2d.globalCompositeOperation = "copy";
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context2DsByHeight[height] = context2d;
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}
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context2d.drawImage(image, 0, 0, width, height);
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return context2d.getImageData(0, 0, width, height).data;
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}
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export default getImagePixels;
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