119 lines
4.1 KiB
JavaScript
119 lines
4.1 KiB
JavaScript
const digitCharacters = [
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"0", "1", "2", "3", "4", "5", "6", "7", "8", "9",
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"A", "B", "C", "D", "E", "F", "G", "H", "I", "J",
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"K", "L", "M", "N", "O", "P", "Q", "R", "S", "T",
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"U", "V", "W", "X", "Y", "Z", "a", "b", "c", "d",
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"e", "f", "g", "h", "i", "j", "k", "l", "m", "n",
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"o", "p", "q", "r", "s", "t", "u", "v", "w", "x",
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"y", "z", "#", "$", "%", "*", "+", ",", "-", ".",
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":", ";", "=", "?", "@", "[", "]", "^", "_", "{",
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"|", "}", "~",
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];
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function decode83(str) {
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let value = 0;
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for (let i = 0; i < str.length; i++) {
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const c = str[i];
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const digit = digitCharacters.indexOf(c);
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value = value * 83 + digit;
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}
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return value;
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}
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function linearTosRGB(value) {
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const v = Math.max(0, Math.min(1, value));
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if (v <= 0.0031308) {
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return Math.round(v * 12.92 * 255 + 0.5);
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}
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else {
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return Math.round((1.055 * Math.pow(v, 1 / 2.4) - 0.055) * 255 + 0.5);
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}
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}
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function sRGBToLinear(value) {
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const v = value / 255;
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if (v <= 0.04045) {
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return v / 12.92;
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}
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else {
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return Math.pow((v + 0.055) / 1.055, 2.4);
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}
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}
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function decodeDC(value) {
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const intR = value >> 16;
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const intG = (value >> 8) & 255;
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const intB = value & 255;
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return [sRGBToLinear(intR), sRGBToLinear(intG), sRGBToLinear(intB)];
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};
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function sign(n) { return (n < 0 ? -1 : 1); }
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function signPow(val, exp) { return sign(val) * Math.pow(Math.abs(val), exp); }
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function decodeDC2(value, maximumValue) {
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const quantR = Math.floor(value / (19 * 19));
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const quantG = Math.floor(value / 19) % 19;
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const quantB = value % 19;
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const rgb = [
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signPow((quantR - 9) / 9, 2.0) * maximumValue,
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signPow((quantG - 9) / 9, 2.0) * maximumValue,
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signPow((quantB - 9) / 9, 2.0) * maximumValue,
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];
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return rgb;
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};
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function decodeblur(blurhash, width, height, punch) {
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punch = punch | 1;
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if (blurhash.length < 6) {
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console.error('too short blurhash');
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return null;
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}
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const sizeFlag = decode83(blurhash[0]);
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const numY = Math.floor(sizeFlag / 9) + 1;
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const numX = (sizeFlag % 9) + 1;
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const quantisedMaximumValue = decode83(blurhash[1]);
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const maximumValue = (quantisedMaximumValue + 1) / 166;
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if (blurhash.length !== 4 + 2 * numX * numY) {
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console.error('blurhash length mismatch', blurhash.length, 4 + 2 * numX * numY);
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return null;
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}
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let colors = new Array(numX * numY);
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for (let i = 0; i < colors.length; i++) {
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if (i === 0) {
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const value = decode83(blurhash.substring(2, 6));
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colors[i] = decodeDC(value);
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}
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else {
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const value = decode83(blurhash.substring(4 + i * 2, 6 + i * 2));
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colors[i] = decodeDC2(value, maximumValue * punch);
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}
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}
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const bytesPerRow = width * 4;
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let pixels = new Uint8ClampedArray(bytesPerRow * height);
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for (var y = 0; y < height; y++) {
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for (var x = 0; x < width; x++) {
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var r = 0;
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var g = 0;
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var b = 0;
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for (let j = 0; j < numY; j++) {
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for (let i = 0; i < numX; i++) {
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let basis = Math.cos(Math.PI * x * i / width) * Math.cos(Math.PI * y * j / height);
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let color = colors[i + j * numX];
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r += color[0] * basis;
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g += color[1] * basis;
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b += color[2] * basis;
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}
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}
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const intR = linearTosRGB(r);
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const intG = linearTosRGB(g);
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const intB = linearTosRGB(b);
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pixels[4 * x + 0 + y * bytesPerRow] = intR;
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pixels[4 * x + 1 + y * bytesPerRow] = intG;
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pixels[4 * x + 2 + y * bytesPerRow] = intB;
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pixels[4 * x + 3 + y * bytesPerRow] = 255; // alpha
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}
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}
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return pixels;
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}
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function parseBlur(blur) {
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const canvas = document.getElementById('canvas');
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const ctx = canvas.getContext('2d');
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const pixels = decodeblur(blur, 32, 32)
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const imageData = new ImageData(pixels, 32, 32);
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ctx.putImageData(imageData, 0, 0);
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return canvas.toDataURL()
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} |