testDrawImage-1.html
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<!DOCTYPE html>
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<html>
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<head>
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<title>Test</title> |
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</head>
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<body>
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<canvas id="canvas"></canvas> |
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<canvas id="canvas2"></canvas> |
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<script type="text/javascript"> |
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var me = {};
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me.isChrome = navigator.userAgent.toLowerCase().indexOf('chrome') > -1;
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/**
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* Returns the Chrome version object if it is applicable, otherwise undefined value.
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*
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* @return The Chrome version object filled with major, minor, build and patch numbers.
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*/
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function getChromeVersion ()
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{
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var parts = navigator.userAgent.match(/Chrom(?:e|ium)\/([0-9]+)\.([0-9]+)\.([0-9]+)\.([0-9]+)/);
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if (parts == null || parts.length != 5) {
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return undefined;
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}
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parts = parts.map(part => parseInt(part, 10));
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return {
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major: parts[1],
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minor: parts[2],
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build: parts[3],
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patch: parts[4]
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};
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}
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/** The Chrome version */
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me.chromeVersion = getChromeVersion();
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/**
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* Creates an offscreen canvas.
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*
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* @returns The new created offscreen canvas
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*/
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function createOffscreenCanvas()
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{
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/** The off screen canvas to be used to make batch drawing. */
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/*if (me.isChrome && me.chromeVersion.major >= 77)
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{
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return new OffscreenCanvas(1, 1);
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}*/
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return document.createElement('canvas');
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}
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/** Defines a method to create an offscreen canvas.*/
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me.createOffscreenCanvas = createOffscreenCanvas;
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/**
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* Tests the screen media if it has a high resolution.
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*
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* @returns {Boolean}
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* True if the screen media has a high resolution.
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*/
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function isHighResolution()
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{
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return window.matchMedia &&
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(window.matchMedia(
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'only screen and (min-resolution: 192dpi), only screen and ' +
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'(min-resolution: 2dppx), ' +
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'only screen and (min-resolution: 75.6dpcm)').matches ||
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window.matchMedia(
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'only screen and (-webkit-min-device-pixel-ratio: 2), only screen and ' +
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'(-o-min-device-pixel-ratio: 2/1), only screen and ' +
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'(min--moz-device-pixel-ratio: 2), only screen and ' +
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'(min-device-pixel-ratio: 2)').matches);
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}
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/** Tests the screen media if it has a high resolution.*/
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me.isHighResolution = isHighResolution;
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// Set display size (css pixels).
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var size = 200;
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var offscreenCanvas = me.createOffscreenCanvas();
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var scale = 1;
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if (me.isHighResolution())
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{
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scale = 2;
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}
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var offscreenCtx = offscreenCanvas.getContext('2d', {'alpha' : true});
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// setup canvas
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offscreenCanvas.style.width = size + "px";
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offscreenCanvas.style.height = size + "px";
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// Set actual size in memory (scaled to account for extra pixel density).
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offscreenCanvas.width = size * scale;
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offscreenCanvas.height = size * scale;
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// Normalize coordinate system to use css pixels.
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offscreenCtx.scale(scale, scale);
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function drawOn(ctx0, scale0, width0, height0, size0)
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{
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// draw on offscreenCanvas
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ctx0.fillStyle = "#bada55";
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ctx0.fillRect(10, 10, size0 - 20, size0 - 20);
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ctx0.fillStyle = "#cbeb66";
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for (var i = 1; i <= (size0 / 10); i++)
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{
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ctx0.fillRect((i-1)*10, (i-1)*10, 10, 10);
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}
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ctx0.fillStyle = "#ffffff";
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ctx0.font = '18px Arial';
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ctx0.textAlign = 'center';
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ctx0.textBaseline = 'middle';
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var x = size0 / 2;
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var y = size0 / 2;
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var textString = "Don't do that until dread";
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ctx0.fillText(textString, x, y);
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ctx0.strokeStyle = "#0000ff";
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ctx0.strokeRect(0, 0, size0, size0);
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var horizontal = ctx0.createImageData(width0, 10 * scale0);
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var bimg = ctx0.getImageData(0, y * scale0, width0, 10 * scale0);
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// Iterate through every pixel
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for (let i = 0; i < horizontal.data.length; i += 4)
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{
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// Modify pixel data
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horizontal.data[i + 0] = 190 ^ bimg.data[i +0]; // R value
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horizontal.data[i + 1] = 0 ^ bimg.data[i +1]; // G value
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horizontal.data[i + 2] = 210 ^ bimg.data[i +2]; // B value
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horizontal.data[i + 3] = 255; // A value
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}
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ctx0.putImageData(horizontal, 0, y * scale0);
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bimg = ctx0.getImageData(x * scale0, 0, 10 * scale0, height0);
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var vertical = ctx0.createImageData(10 * scale0, height0);
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// Iterate through every pixel
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for (let i = 0; i < vertical.data.length; i += 4)
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{
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// Modify pixel data
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vertical.data[i + 0] = 190 ^ bimg.data[i +0]; // R value
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vertical.data[i + 1] = 0 ^ bimg.data[i +1]; // G value
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vertical.data[i + 2] = 210 ^ bimg.data[i +2]; // B value
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vertical.data[i + 3] = 255; // A value
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}
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ctx0.putImageData(vertical, x * scale0, 0);
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};
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drawOn(offscreenCtx, scale, offscreenCanvas.width, offscreenCanvas.height, size);
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var image = offscreenCtx.getImageData(0, 0, offscreenCanvas.width, offscreenCanvas.height);
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var canvas = document.getElementById('canvas');
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// setup canvas
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canvas.style.width = size + "px";
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canvas.style.height = size + "px";
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canvas.width = size * scale;
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canvas.height = size * scale;
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var ctx = canvas.getContext('2d', {'alpha' : true});
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// Normalize coordinate system to use css pixels.
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ctx.scale(scale, scale);
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ctx.putImageData(image, 0, 0);
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// draw on canvas2 directly without scaling
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var canvas2 = document.getElementById('canvas2');
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// setup canvas
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canvas2.style.width = size + "px";
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canvas2.style.height = size + "px";
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canvas2.width = size;
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canvas2.height = size;
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var ctx2 = canvas2.getContext('2d', {'alpha' : true});
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drawOn(ctx2, 1, canvas2.width, canvas2.height, size);
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</script>
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</body>
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</html>
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