added a new library for fir canvas on ios/safari
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Mario Colque
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83681967df
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/**
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* Mega pixel image rendering library for iOS6 Safari
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*
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* Fixes iOS6 Safari's image file rendering issue for large size image (over mega-pixel),
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* which causes unexpected subsampling when drawing it in canvas.
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* By using this library, you can safely render the image with proper stretching.
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*
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* Copyright (c) 2012 Shinichi Tomita <shinichi.tomita@gmail.com>
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* Released under the MIT license
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*/
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(function() {
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/**
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* Detect subsampling in loaded image.
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* In iOS, larger images than 2M pixels may be subsampled in rendering.
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*/
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function detectSubsampling(img) {
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var iw = img.naturalWidth, ih = img.naturalHeight;
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if (iw * ih > 1024 * 1024) { // subsampling may happen over megapixel image
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var canvas = document.createElement('canvas');
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canvas.width = canvas.height = 1;
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var ctx = canvas.getContext('2d');
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ctx.drawImage(img, -iw + 1, 0);
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// subsampled image becomes half smaller in rendering size.
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// check alpha channel value to confirm image is covering edge pixel or not.
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// if alpha value is 0 image is not covering, hence subsampled.
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return ctx.getImageData(0, 0, 1, 1).data[3] === 0;
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} else {
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return false;
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}
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}
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/**
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* Detecting vertical squash in loaded image.
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* Fixes a bug which squash image vertically while drawing into canvas for some images.
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*/
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function detectVerticalSquash(img, iw, ih) {
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var canvas = document.createElement('canvas');
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canvas.width = 1;
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canvas.height = ih;
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var ctx = canvas.getContext('2d');
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ctx.drawImage(img, 0, 0);
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var data = ctx.getImageData(0, 0, 1, ih).data;
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// search image edge pixel position in case it is squashed vertically.
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var sy = 0;
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var ey = ih;
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var py = ih;
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while (py > sy) {
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var alpha = data[(py - 1) * 4 + 3];
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if (alpha === 0) {
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ey = py;
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} else {
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sy = py;
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}
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py = (ey + sy) >> 1;
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}
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var ratio = (py / ih);
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return (ratio===0)?1:ratio;
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}
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/**
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* Rendering image element (with resizing) and get its data URL
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*/
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function renderImageToDataURL(img, options, doSquash) {
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var canvas = document.createElement('canvas');
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renderImageToCanvas(img, canvas, options, doSquash);
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return canvas.toDataURL("image/jpeg", options.quality || 0.8);
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}
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/**
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* Rendering image element (with resizing) into the canvas element
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*/
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function renderImageToCanvas(img, canvas, options, doSquash) {
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var iw = img.naturalWidth, ih = img.naturalHeight;
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var width = options.width, height = options.height;
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var ctx = canvas.getContext('2d');
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ctx.save();
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transformCoordinate(canvas, width, height, options.orientation);
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var subsampled = detectSubsampling(img);
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if (subsampled) {
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iw /= 2;
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ih /= 2;
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}
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var d = 1024; // size of tiling canvas
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var tmpCanvas = document.createElement('canvas');
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tmpCanvas.width = tmpCanvas.height = d;
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var tmpCtx = tmpCanvas.getContext('2d');
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var vertSquashRatio = doSquash ? detectVerticalSquash(img, iw, ih) : 1;
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var dw = Math.ceil(d * width / iw);
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var dh = Math.ceil(d * height / ih / vertSquashRatio);
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var sy = 0;
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var dy = 0;
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while (sy < ih) {
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var sx = 0;
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var dx = 0;
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while (sx < iw) {
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tmpCtx.clearRect(0, 0, d, d);
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tmpCtx.drawImage(img, -sx, -sy);
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ctx.drawImage(tmpCanvas, 0, 0, d, d, dx, dy, dw, dh);
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sx += d;
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dx += dw;
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}
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sy += d;
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dy += dh;
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}
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ctx.restore();
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tmpCanvas = tmpCtx = null;
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}
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/**
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* Transform canvas coordination according to specified frame size and orientation
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* Orientation value is from EXIF tag
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*/
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function transformCoordinate(canvas, width, height, orientation) {
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switch (orientation) {
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case 5:
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case 6:
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case 7:
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case 8:
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canvas.width = height;
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canvas.height = width;
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break;
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default:
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canvas.width = width;
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canvas.height = height;
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}
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var ctx = canvas.getContext('2d');
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switch (orientation) {
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case 2:
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// horizontal flip
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ctx.translate(width, 0);
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ctx.scale(-1, 1);
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break;
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case 3:
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// 180 rotate left
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ctx.translate(width, height);
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ctx.rotate(Math.PI);
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break;
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case 4:
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// vertical flip
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ctx.translate(0, height);
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ctx.scale(1, -1);
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break;
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case 5:
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// vertical flip + 90 rotate right
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ctx.rotate(0.5 * Math.PI);
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ctx.scale(1, -1);
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break;
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case 6:
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// 90 rotate right
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ctx.rotate(0.5 * Math.PI);
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ctx.translate(0, -height);
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break;
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case 7:
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// horizontal flip + 90 rotate right
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ctx.rotate(0.5 * Math.PI);
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ctx.translate(width, -height);
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ctx.scale(-1, 1);
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break;
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case 8:
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// 90 rotate left
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ctx.rotate(-0.5 * Math.PI);
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ctx.translate(-width, 0);
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break;
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default:
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break;
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}
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}
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/**
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* MegaPixImage class
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*/
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function MegaPixImage(srcImage) {
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if (window.Blob && srcImage instanceof Blob) {
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var img = new Image();
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var URL = window.URL && window.URL.createObjectURL ? window.URL :
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window.webkitURL && window.webkitURL.createObjectURL ? window.webkitURL :
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null;
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if (!URL) { throw Error("No createObjectURL function found to create blob url"); }
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img.src = URL.createObjectURL(srcImage);
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this.blob = srcImage;
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srcImage = img;
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}
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if (!srcImage.naturalWidth && !srcImage.naturalHeight) {
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var _this = this;
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srcImage.onload = function() {
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var listeners = _this.imageLoadListeners;
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if (listeners) {
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_this.imageLoadListeners = null;
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for (var i=0, len=listeners.length; i<len; i++) {
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listeners[i]();
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}
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}
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};
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this.imageLoadListeners = [];
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}
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this.srcImage = srcImage;
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}
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/**
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* Rendering megapix image into specified target element
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*/
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MegaPixImage.prototype.render = function(target, options) {
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if (this.imageLoadListeners) {
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var _this = this;
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this.imageLoadListeners.push(function() { _this.render(target, options) });
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return;
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}
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options = options || {};
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var imgWidth = this.srcImage.naturalWidth, imgHeight = this.srcImage.naturalHeight,
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width = options.width, height = options.height,
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maxWidth = options.maxWidth, maxHeight = options.maxHeight,
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doSquash = !this.blob || this.blob.type === 'image/jpeg';
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if (width && !height) {
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height = (imgHeight * width / imgWidth) << 0;
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} else if (height && !width) {
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width = (imgWidth * height / imgHeight) << 0;
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} else {
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width = imgWidth;
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height = imgHeight;
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}
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if (maxWidth && width > maxWidth) {
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width = maxWidth;
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height = (imgHeight * width / imgWidth) << 0;
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}
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if (maxHeight && height > maxHeight) {
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height = maxHeight;
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width = (imgWidth * height / imgHeight) << 0;
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}
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var opt = { width : width, height : height };
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for (var k in options) opt[k] = options[k];
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var tagName = target.tagName.toLowerCase();
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if (tagName === 'img') {
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target.src = renderImageToDataURL(this.srcImage, opt, doSquash);
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} else if (tagName === 'canvas') {
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renderImageToCanvas(this.srcImage, target, opt, doSquash);
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}
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if (typeof this.onrender === 'function') {
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this.onrender(target);
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}
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};
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/**
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* Export class to global
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*/
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if (typeof define === 'function' && define.amd) {
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define([], function() { return MegaPixImage; }); // for AMD loader
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} else {
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this.MegaPixImage = MegaPixImage;
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}
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})();
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