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kaiwa/clientapp/libraries/resampler.js
2013-09-18 16:24:40 -07:00

115 lines
2.8 KiB
JavaScript

var Resample = (function (canvas) {
// (C) WebReflection Mit Style License
// Resample function, accepts an image
// as url, base64 string, or Image/HTMLImgElement
// optional width or height, and a callback
// to invoke on operation complete
function Resample(img, width, height, onresample) {
var
// check the image type
load = typeof img == "string",
// Image pointer
i = load || img
;
// if string, a new Image is needed
if (load) {
i = new Image;
// with propers callbacks
i.onload = onload;
i.onerror = onerror;
}
// easy/cheap way to store info
i._onresample = onresample;
i._width = width;
i._height = height;
// if string, we trust the onload event
// otherwise we call onload directly
// with the image as callback context
load ? (i.src = img) : onload.call(img);
}
// just in case something goes wrong
function onerror() {
throw ("not found: " + this.src);
}
// called when the Image is ready
function onload() {
var
// minifier friendly
img = this,
// the desired width, if any
width = img._width,
// the desired height, if any
height = img._height,
// the callback
onresample = img._onresample
;
// if width and height are both specified
// the resample uses these pixels
// if width is specified but not the height
// the resample respects proportions
// accordingly with orginal size
// same is if there is a height, but no width
width == null && (width = round(img.width * height / img.height));
height == null && (height = round(img.height * width / img.width));
// remove (hopefully) stored info
delete img._onresample;
delete img._width;
delete img._height;
// when we reassign a canvas size
// this clears automatically
// the size should be exactly the same
// of the final image
// so that toDataURL ctx method
// will return the whole canvas as png
// without empty spaces or lines
canvas.width = width;
canvas.height = height;
// drawImage has different overloads
// in this case we need the following one ...
context.drawImage(
// original image
img,
// starting x point
0,
// starting y point
0,
// image width
img.width,
// image height
img.height,
// destination x point
0,
// destination y point
0,
// destination width
width,
// destination height
height
);
// retrieve the canvas content as
// base4 encoded PNG image
// and pass the result to the callback
onresample(canvas.toDataURL("image/png"));
}
var
// point one, use every time ...
context = canvas.getContext("2d"),
// local scope shortcut
round = Math.round
;
return Resample;
}(
// lucky us we don't even need to append
// and render anything on the screen
// let's keep this DOM node in RAM
// for all resizes we want
this.document.createElement("canvas"))
);