todataurl.js

/* -*- mode:javascript; coding:utf-8; -*- Time-stamp: <todataurl.js - root> */

Number.prototype.toUInt=function(){ return this<0?this+4294967296:this; };
Number.prototype.bytes32=function(){ return [(this>>>24)&0xff,(this>>>16)&0xff,(this>>>8)&0xff,this&0xff]; };
Number.prototype.bytes32sw=function(){ return [this&0xff,(this>>>8)&0xff,(this>>>16)&0xff,(this>>>24)&0xff]; };
Number.prototype.bytes16=function(){ return [(this>>>8)&0xff,this&0xff]; };
Number.prototype.bytes16sw=function(){ return [this&0xff,(this>>>8)&0xff]; };

Array.prototype.adler32=function(start,len){
	switch(arguments.length){ case 0:start=0; case 1:len=this.length-start; }
	var a=1,b=0;
	for(var i=0;i<len;i++){
		a = (a+this[start+i])%65521; b = (b+a)%65521;
	}
	return ((b << 16) | a).toUInt();
};

Array.prototype.crc32=function(start,len){
	switch(arguments.length){ case 0:start=0; case 1:len=this.length-start; }
	var table=arguments.callee.crctable;
	if(!table){
		table=[];
		var c;
		for (var n = 0; n < 256; n++) {
			c = n;
			for (var k = 0; k < 8; k++)
				c = c & 1?0xedb88320 ^ (c >>> 1):c >>> 1;
			table[n] = c.toUInt();
		}
		arguments.callee.crctable=table;
	}
	var c = 0xffffffff;
	for (var i = 0; i < len; i++)
		c = table[(c ^ this[start+i]) & 0xff] ^ (c>>>8);
	return (c^0xffffffff).toUInt();
};

(function(){
	var toDataURL=function(){
		var imageData=Array.prototype.slice.call(this.getContext("2d").getImageData(0,0,this.width,this.height).data);
		var w=this.width;
		var h=this.height;
		var stream=[
			0x89,0x50,0x4e,0x47,0x0d,0x0a,0x1a,0x0a,
			0x00,0x00,0x00,0x0d,0x49,0x48,0x44,0x52
		];
		Array.prototype.push.apply(stream, w.bytes32() );
		Array.prototype.push.apply(stream, h.bytes32() );
		stream.push(0x08,0x06,0x00,0x00,0x00);
		Array.prototype.push.apply(stream, stream.crc32(12,17).bytes32() );
		var len=h*(w*4+1);
		for(var y=0;y<h;y++)
			imageData.splice(y*(w*4+1),0,0);
		var blocks=Math.ceil(len/32768);
		Array.prototype.push.apply(stream, (len+5*blocks+6).bytes32() );
		var crcStart=stream.length;
		var crcLen=(len+5*blocks+6+4);
		stream.push(0x49,0x44,0x41,0x54,0x78,0x01);
		for(var i=0;i<blocks;i++){
			var blockLen=Math.min(32768,len-(i*32768));
			stream.push(i==(blocks-1)?0x01:0x00);
			Array.prototype.push.apply(stream, blockLen.bytes16sw() );
			Array.prototype.push.apply(stream, (~blockLen).bytes16sw() );
			var id=imageData.slice(i*32768,i*32768+blockLen);
			Array.prototype.push.apply(stream, id );
		}
		Array.prototype.push.apply(stream, imageData.adler32().bytes32() );
		Array.prototype.push.apply(stream, stream.crc32(crcStart, crcLen).bytes32() );
		stream.push(0x00,0x00,0x00,0x00,0x49,0x45,0x4e,0x44);
		Array.prototype.push.apply(stream, stream.crc32(stream.length-4, 4).bytes32() );
		return "data:image/png;base64,"+btoa(String.fromCharCode.apply(null,stream));
	};

	var tdu=HTMLCanvasElement.prototype.toDataURL;

	HTMLCanvasElement.prototype.toDataURL=function(type){
		var res=tdu.apply(this,arguments);
		if(res.substr(0,6)=="data:,"){
			HTMLCanvasElement.prototype.toDataURL=toDataURL;
			return this.toDataURL();
		}else{
			HTMLCanvasElement.prototype.toDataURL=tdu;
			return res;
		}
	}
})();