canvas-toBlob.js

/* canvas-toBlob.js
 * A canvas.toBlob() implementation.
 * 2011-07-13
 * 
 * By Eli Grey, http://eligrey.com and Devin Samarin, https://github.com/eboyjr
 * License: X11/MIT
 *   See LICENSE.md
 */

/*global self */
/*jslint bitwise: true, regexp: true, confusion: true, es5: true, vars: true, white: true,
  plusplus: true */

/*! @source http://purl.eligrey.com/github/canvas-toBlob.js/blob/master/canvas-toBlob.js */

(function(view) {
"use strict";
var
    Uint8Array = view.Uint8Array
	, HTMLCanvasElement = view.HTMLCanvasElement
	, is_base64_regex = /\s*;\s*base64\s*(?:;|$)/i
	, base64_ranks
	, decode_base64 = function(base64) {
		var
			  len = base64.length
			, buffer = new Uint8Array(len / 4 * 3 | 0)
			, i = 0
			, outptr = 0
			, last = [0, 0]
			, state = 0
			, save = 0
			, rank
			, code
			, undef
		;
		while (len--) {
			code = base64.charCodeAt(i++);
			rank = base64_ranks[code-43];
			if (rank !== 255 && rank !== undef) {
				last[1] = last[0];
				last[0] = code;
				save = (save << 6) | rank;
				state++;
				if (state === 4) {
					buffer[outptr++] = save >>> 16;
					if (last[1] !== 61 /* padding character */) {
						buffer[outptr++] = save >>> 8;
					}
					if (last[0] !== 61 /* padding character */) {
						buffer[outptr++] = save;
					}
					state = 0;
				}
			}
		}
		// 2/3 chance there's going to be some null bytes at the end, but that
		// doesn't really matter with most image formats.
		// If it somehow matters for you, truncate the buffer up outptr.
		return buffer.buffer;
	}
;
if (Uint8Array) {
	base64_ranks = new Uint8Array([
		  62, -1, -1, -1, 63, 52, 53, 54, 55, 56, 57, 58, 59, 60, 61, -1
		, -1, -1,  0, -1, -1, -1,  0,  1,  2,  3,  4,  5,  6,  7,  8,  9
		, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25
		, -1, -1, -1, -1, -1, -1, 26, 27, 28, 29, 30, 31, 32, 33, 34, 35
		, 36, 37, 38, 39, 40, 41, 42, 43, 44, 45, 46, 47, 48, 49, 50, 51
	]);
}
if (HTMLCanvasElement && !HTMLCanvasElement.prototype.toBlob) {
	HTMLCanvasElement.prototype.toBlob = function(callback, type /*, ...args*/) {
		  if (!type) {
			type = "image/png";
		} if (this.mozGetAsFile) {
			callback(this.mozGetAsFile("canvas", type));
			return;
		}
		var
			  args = Array.prototype.slice.call(arguments, 1)
			, dataURI = this.toDataURL.apply(this, args)
			, header_end = dataURI.indexOf(",")
			, data = dataURI.substring(header_end + 1)
			, is_base64 = is_base64_regex.test(dataURI.substring(0, header_end))
			, blob
		;
		if (Blob.fake) {
			// no reason to decode a data: URI that's just going to become a data URI again
			blob = new Blob
			if (is_base64) {
				blob.encoding = "base64";
			} else {
				blob.encoding = "URI";
			}
			blob.data = data;
			blob.size = data.length;
		} else if (Uint8Array) {
			if (is_base64) {
				blob = new Blob([decode_base64(data)], {type: type});
			} else {
				blob = new Blob([decodeURIComponent(data)], {type: type});
			}
		}
		callback(blob);
	};
}
}(self));