245 lines
9.4 KiB
HTML
245 lines
9.4 KiB
HTML
<!DOCTYPE html>
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<html>
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<head>
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<meta charset="utf-8">
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<title>Block video encoding test</title>
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<style type="text/css">
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.stretchy {
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width: 320px;
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height: 192px;
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object-fit: fill;
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image-rendering: pixelated;
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}
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</style>
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</head>
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<body>
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<h1>Block video encoding test</h1>
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<p>
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Test work for a video encoding using Atari 800-family GTIA grayscale mode on top of text cells.
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This allows a "block dictionary" of 128 2x8-pixel blocks on an 80x160 grayscale image,
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at cost of 1840 bytes per full frame or 800 bytes to reuse previous blocks.
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</p>
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<p>
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Currently converts to grayscale and reuses existing similar blocks as it goes,
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increasing a similarity threshold (from 0) until the set fits in 128 chars.
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'Inverse video' characters should be correctly taken into account.
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Further step: don't end up stuck between 64 and 128 blocks :D Try to weight decimation by use or something.
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</p>
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<div>
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<video id="source" src="llamigos.webm" class="stretchy" muted controls playsinline></video>
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<canvas id="work" width="80" height="160" class="stretchy"></canvas>
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<canvas id="font" width="80" height="160" class="stretchy"></canvas>
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</div>
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<div>
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<span id="block-count">n/a</span> unique blocks per frame
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</div>
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<script type="text/javascript">
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let width = 80;
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let height = 160;
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let blockWidth = 2;
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let blockHeight = 8;
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let widthBlocks = width / blockWidth;
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let heightBlocks = height / blockHeight;
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function fromSRGB(val) {
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if (val <= 0.04045) {
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return val / 12.92;
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}
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return ((val + 0.055) / 1.055) ** 2.4;
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}
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function toSRGB(val) {
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if (val <= 0.0031308) {
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return val * 12.92;
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}
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return (val * 1.055) ** (1.0 / 2.4) - 0.055;
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}
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function luma(r, g, b) {
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return r * 0.299 + g * 0.586 + b * 0.114;
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}
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function hexify(block) {
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return Array.from(block).map((n) => n.toString(16)).join('');
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}
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function inverse(pixel) {
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return ~pixel & 0xf;
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}
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function matchBlocks(a, b, threshold) {
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for (let i = 0; i < blockWidth * blockHeight; i++) {
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if (Math.abs(a[i] - b[i]) > threshold) {
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return false;
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}
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}
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return true;
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}
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function matchBlocksInverse(a, b, threshold) {
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for (let i = 0; i < blockWidth * blockHeight; i++) {
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if (Math.abs(a[i] - inverse(b[i])) > threshold) {
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return false;
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}
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}
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return true;
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}
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function drawChar(imageData, cx, cy, char, charset) {
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let invert = Boolean(char & 0x80);
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char &= 0x7f;
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if (char >= charset.length) {
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return;
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}
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let block = charset[char];
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for (let y = 0; y < blockHeight; y++) {
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for (let x = 0; x < blockWidth; x++) {
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let i = y * blockWidth + x;
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let ii = (y + cy * blockHeight) * imageData.width + (x + cx * blockWidth);
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let gray16 = block[i];
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if (invert) {
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gray16 = inverse(gray16);
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}
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let gray256 = Math.round(gray16 * 255 / 15);
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imageData.data[ii * 4] = gray256;
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imageData.data[ii * 4 + 1] = gray256;
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imageData.data[ii * 4 + 2] = gray256;
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imageData.data[ii * 4 + 3] = 255;
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}
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}
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}
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function update() {
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let ctx = work.getContext('2d');
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let pixels = new Uint8Array(width * height);
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// Extract the luma
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ctx.drawImage(source, 0, 0);
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let bits = ctx.getImageData(0, 0, width, height);
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let data = bits.data;
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for (let y = 0; y < height; y++) {
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for (let x = 0; x < width; x++) {
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let i = y * width + x;
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let r = fromSRGB(data[i * 4] / 255);
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let g = fromSRGB(data[i * 4 + 1] / 255);
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let b = fromSRGB(data[i * 4 + 2] / 255);
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let grayLinear = luma(r, g, b);
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let gray = toSRGB(grayLinear);
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let gray16 = Math.round(gray * 15);
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pixels[i] = gray16;
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}
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}
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let blocks = [];
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let chars = new Uint16Array(widthBlocks * heightBlocks);
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for (y = 0; y < heightBlocks; y++) {
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for (let x = 0; x < widthBlocks; x++) {
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let i = y * widthBlocks + x;
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blocks[i] = new Uint8Array(blockWidth * blockHeight);
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chars[i] = i;
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for (let yy = 0; yy < blockHeight; yy++) {
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for (let xx = 0; xx < blockWidth; xx++) {
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let ii = yy * blockWidth + xx;
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blocks[i][ii] = pixels[(y * blockHeight + yy) * width + (x * blockWidth + xx)];
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}
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}
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}
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}
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// Now we have 800 blocks for 80x160 image
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// But we can only use 128 + their mirror images
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//
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// First pass: uniques extraction
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// Convert the 4bpp pixel indices into hex strings
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let uniques = [];
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for (let threshold = 0; threshold < 16; threshold++) {
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charIter:
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for (let i = 0; i < blocks.length; i++) {
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let block = blocks[i];
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fontMatch:
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for (let j = 0; j < uniques.length; j++) {
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let other = uniques[j];
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if (!block) {
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debugger
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throw new Error('missing other');
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}
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if (matchBlocks(block, other, threshold)) {
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// we're close enough to reuse a character
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chars[i] = j;
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continue charIter;
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} else if (matchBlocksInverse(block, other, threshold)) {
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chars[i] = j | 0x8000;
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continue charIter;
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} else {
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continue fontMatch;
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}
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}
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// add a new char
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chars[i] = uniques.push(block) - 1;
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}
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if (uniques.length < 128) {
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break;
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}
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// We need to decimate further
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uniques = [];
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}
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let span = document.querySelector('#block-count');
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span.textContent = `${uniques.length}`;
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// Font
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let fontCtx = document.querySelector('#font').getContext('2d');
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let font = fontCtx.createImageData(16 * blockWidth, 16 * blockHeight);
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for (let hi = 0; hi < 16; hi++) {
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for (let lo = 0; lo < 16; lo++) {
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let char = (hi << 4) | lo;
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drawChar(font, lo, hi, char, uniques);
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}
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}
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fontCtx.putImageData(font, 0, 0);
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// Redraw the blocks
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for (let cy = 0; cy < heightBlocks; cy++) {
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for (let cx = 0; cx < widthBlocks; cx++) {
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let i = cy * widthBlocks + cx;
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let char = chars[i];
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if (char & 0x8000) {
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// we use a bigger bit during earlier stages
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char &= 0x7f;
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char |= 0x80;
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}
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drawChar(bits, cx, cy, char, uniques);
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}
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}
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ctx.putImageData(bits, 0, 0);
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}
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let timer = null;
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source.addEventListener('playing', () => {
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if (!timer) {
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// target 8 fps
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// not sure we can get any faster
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// downloads over sio
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timer = setInterval(update, 1000 / 8);
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}
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update();
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});
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source.addEventListener('pause', () => {
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if (timer) {
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clearInterval(timer);
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timer = null;
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}
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});
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</script>
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</body>
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</html> |