https://www.sgi-network.org/js/export/canvas-toBlob.js

1/* canvas-toBlob.js
2 * A canvas.toBlob() implementation.
3 * 2016-05-26
4 * 
5 * By Eli Grey, http://eligrey.com and Devin Samarin, https://github.com/eboyjr
6 * License: MIT
7 *   See https://github.com/eligrey/canvas-toBlob.js/blob/master/LICENSE.md
8 */
9
10/*global self */
11/*jslint bitwise: true, regexp: true, confusion: true, es5: true, vars: true, white: true,
12  plusplus: true */
13
14/*! @source http://purl.eligrey.com/github/canvas-toBlob.js/blob/master/canvas-toBlob.js */
15
16(function(view) {
17"use strict";
18var
19	  Uint8Array = view.Uint8Array
20	, HTMLCanvasElement = view.HTMLCanvasElement
21	, canvas_proto = HTMLCanvasElement && HTMLCanvasElement.prototype
22	, is_base64_regex = /\s*;\s*base64\s*(?:;|$)/i
23	, to_data_url = "toDataURL"
24	, base64_ranks
25	, decode_base64 = function(base64) {
26		var
27			  len = base64.length
28			, buffer = new Uint8Array(len / 4 * 3 | 0)
29			, i = 0
30			, outptr = 0
31			, last = [0, 0]
32			, state = 0
33			, save = 0
34			, rank
35			, code
36			, undef
37		;
38		while (len--) {
39			code = base64.charCodeAt(i++);
40			rank = base64_ranks[code-43];
41			if (rank !== 255 && rank !== undef) {
42				last[1] = last[0];
43				last[0] = code;
44				save = (save << 6) | rank;
45				state++;
46				if (state === 4) {
47					buffer[outptr++] = save >>> 16;
48					if (last[1] !== 61 /* padding character */) {
49						buffer[outptr++] = save >>> 8;
50					}
51					if (last[0] !== 61 /* padding character */) {
52						buffer[outptr++] = save;
53					}
54					state = 0;
55				}
56			}
57		}
58		// 2/3 chance there's going to be some null bytes at the end, but that
59		// doesn't really matter with most image formats.
60		// If it somehow matters for you, truncate the buffer up outptr.
61		return buffer;
62	}
63;
64if (Uint8Array) {
65	base64_ranks = new Uint8Array([
66		  62, -1, -1, -1, 63, 52, 53, 54, 55, 56, 57, 58, 59, 60, 61, -1
67		, -1, -1,  0, -1, -1, -1,  0,  1,  2,  3,  4,  5,  6,  7,  8,  9
68		, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25
69		, -1, -1, -1, -1, -1, -1, 26, 27, 28, 29, 30, 31, 32, 33, 34, 35
70		, 36, 37, 38, 39, 40, 41, 42, 43, 44, 45, 46, 47, 48, 49, 50, 51
71	]);
72}
73if (HTMLCanvasElement && (!canvas_proto.toBlob || !canvas_proto.toBlobHD)) {
74	if (!canvas_proto.toBlob)
75	canvas_proto.toBlob = function(callback, type /*, ...args*/) {
76		  if (!type) {
77			type = "image/png";
78		} if (this.mozGetAsFile) {
79			callback(this.mozGetAsFile("canvas", type));
80			return;
81		} if (this.msToBlob && /^\s*image\/png\s*(?:$|;)/i.test(type)) {
82			callback(this.msToBlob());
83			return;
84		}
85
86		var
87			  args = Array.prototype.slice.call(arguments, 1)
88			, dataURI = this[to_data_url].apply(this, args)
89			, header_end = dataURI.indexOf(",")
90			, data = dataURI.substring(header_end + 1)
91			, is_base64 = is_base64_regex.test(dataURI.substring(0, header_end))
92			, blob
93		;
94		if (Blob.fake) {
95			// no reason to decode a data: URI that's just going to become a data URI again
96			blob = new Blob
97			if (is_base64) {
98				blob.encoding = "base64";
99			} else {
100				blob.encoding = "URI";
101			}
102			blob.data = data;
103			blob.size = data.length;
104		} else if (Uint8Array) {
105			if (is_base64) {
106				blob = new Blob([decode_base64(data)], {type: type});
107			} else {
108				blob = new Blob([decodeURIComponent(data)], {type: type});
109			}
110		}
111		callback(blob);
112	};
113
114	if (!canvas_proto.toBlobHD && canvas_proto.toDataURLHD) {
115		canvas_proto.toBlobHD = function() {
116			to_data_url = "toDataURLHD";
117			var blob = this.toBlob();
118			to_data_url = "toDataURL";
119			return blob;
120		}
121	} else {
122		canvas_proto.toBlobHD = canvas_proto.toBlob;
123	}
124}
125}(typeof self !== "undefined" && self || typeof window !== "undefined" && window || this.content || this));