load-image-ios.js
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/*
* JavaScript Load Image iOS scaling fixes 1.0.3
* https://github.com/blueimp/JavaScript-Load-Image
*
* Copyright 2013, Sebastian Tschan
* https://blueimp.net
*
* iOS image scaling fixes based on
* https://github.com/stomita/ios-imagefile-megapixel
*
* Licensed under the MIT license:
* http://www.opensource.org/licenses/MIT
*/
/*jslint nomen: true, bitwise: true */
/*global define, window, document */
(function (factory) {
'use strict';
if (typeof define === 'function' && define.amd) {
// Register as an anonymous AMD module:
define(['load-image'], factory);
} else {
// Browser globals:
factory(window.loadImage);
}
}(function (loadImage) {
'use strict';
// Only apply fixes on the iOS platform:
if (!window.navigator || !window.navigator.platform ||
!(/iP(hone|od|ad)/).test(window.navigator.platform)) {
return;
}
var originalRenderMethod = loadImage.renderImageToCanvas;
// Detects subsampling in JPEG images:
loadImage.detectSubsampling = function (img) {
var canvas,
context;
if (img.width * img.height > 1024 * 1024) { // only consider mexapixel images
canvas = document.createElement('canvas');
canvas.width = canvas.height = 1;
context = canvas.getContext('2d');
context.drawImage(img, -img.width + 1, 0);
// subsampled image becomes half smaller in rendering size.
// check alpha channel value to confirm image is covering edge pixel or not.
// if alpha value is 0 image is not covering, hence subsampled.
return context.getImageData(0, 0, 1, 1).data[3] === 0;
}
return false;
};
// Detects vertical squash in JPEG images:
loadImage.detectVerticalSquash = function (img, subsampled) {
var naturalHeight = img.naturalHeight || img.height,
canvas = document.createElement('canvas'),
context = canvas.getContext('2d'),
data,
sy,
ey,
py,
alpha;
if (subsampled) {
naturalHeight /= 2;
}
canvas.width = 1;
canvas.height = naturalHeight;
context.drawImage(img, 0, 0);
data = context.getImageData(0, 0, 1, naturalHeight).data;
// search image edge pixel position in case it is squashed vertically:
sy = 0;
ey = naturalHeight;
py = naturalHeight;
while (py > sy) {
alpha = data[(py - 1) * 4 + 3];
if (alpha === 0) {
ey = py;
} else {
sy = py;
}
py = (ey + sy) >> 1;
}
return (py / naturalHeight) || 1;
};
// Renders image to canvas while working around iOS image scaling bugs:
// https://github.com/blueimp/JavaScript-Load-Image/issues/13
loadImage.renderImageToCanvas = function (
canvas,
img,
sourceX,
sourceY,
sourceWidth,
sourceHeight,
destX,
destY,
destWidth,
destHeight
) {
if (img._type === 'image/jpeg') {
var context = canvas.getContext('2d'),
tmpCanvas = document.createElement('canvas'),
tileSize = 1024,
tmpContext = tmpCanvas.getContext('2d'),
subsampled,
vertSquashRatio,
tileX,
tileY;
tmpCanvas.width = tileSize;
tmpCanvas.height = tileSize;
context.save();
subsampled = loadImage.detectSubsampling(img);
if (subsampled) {
sourceX /= 2;
sourceY /= 2;
sourceWidth /= 2;
sourceHeight /= 2;
}
vertSquashRatio = loadImage.detectVerticalSquash(img, subsampled);
if (subsampled || vertSquashRatio !== 1) {
sourceY *= vertSquashRatio;
destWidth = Math.ceil(tileSize * destWidth / sourceWidth);
destHeight = Math.ceil(
tileSize * destHeight / sourceHeight / vertSquashRatio
);
destY = 0;
tileY = 0;
while (tileY < sourceHeight) {
destX = 0;
tileX = 0;
while (tileX < sourceWidth) {
tmpContext.clearRect(0, 0, tileSize, tileSize);
tmpContext.drawImage(
img,
sourceX,
sourceY,
sourceWidth,
sourceHeight,
-tileX,
-tileY,
sourceWidth,
sourceHeight
);
context.drawImage(
tmpCanvas,
0,
0,
tileSize,
tileSize,
destX,
destY,
destWidth,
destHeight
);
tileX += tileSize;
destX += destWidth;
}
tileY += tileSize;
destY += destHeight;
}
context.restore();
return canvas;
}
}
return originalRenderMethod(
canvas,
img,
sourceX,
sourceY,
sourceWidth,
sourceHeight,
destX,
destY,
destWidth,
destHeight
);
};
}));