if (window.CanvasRenderingContext2D && CanvasRenderingContext2D.prototype.getImageData){
	var defaultOffsets = {
	destX : 0,
	destY : 0,
	sourceX : 0,
	sourceY : 0,
	width : 'auto',
	height : 'auto'
	};
	CanvasRenderingContext2D.prototype.blendOnto = function(destContext,blendMode,offsetOptions){
	var offsets={};
	for (var key in defaultOffsets){
	if (defaultOffsets.hasOwnProperty(key)){
	offsets[key] = (offsetOptions && offsetOptions[key]) || defaultOffsets[key];
	}
	}
	if (offsets.width =='auto') offsets.width =this.canvas.width;
	if (offsets.height=='auto') offsets.height=this.canvas.height;
	offsets.width = Math.min(offsets.width, this.canvas.width-offsets.sourceX, destContext.canvas.width-offsets.destX );
	offsets.height = Math.min(offsets.height,this.canvas.height-offsets.sourceY,destContext.canvas.height-offsets.destY);
	
	var srcD = this.getImageData(offsets.sourceX,offsets.sourceY,offsets.width,offsets.height);
	var dstD = destContext.getImageData(offsets.destX,offsets.destY,offsets.width,offsets.height);
	var src = srcD.data;
	var dst = dstD.data;
	var sA, dA, len=dst.length;
	var sRA, sGA, sBA, dRA, dGA, dBA, dA2;
	var demultiply;
	
	for (var px=0;px<len;px+=4){
	sA = src[px+3]/255;
	dA = dst[px+3]/255;
	dA2 = (sA + dA - sA*dA);
	dst[px+3] = dA2*255;
	
	sRA = src[px ]/255*sA;
	dRA = dst[px ]/255*dA;
	sGA = src[px+1]/255*sA;
	dGA = dst[px+1]/255*dA;
	sBA = src[px+2]/255*sA;
	dBA = dst[px+2]/255*dA;
	
	demultiply = 255 / dA2;
	
	switch(blendMode){
	// ******* Very close match to Photoshop
	case 'normal':
	case 'src-over':
	dst[px ] = (sRA + dRA - dRA*sA) * demultiply;
	dst[px+1] = (sGA + dGA - dGA*sA) * demultiply;
	dst[px+2] = (sBA + dBA - dBA*sA) * demultiply;
	break;
	
	case 'screen':
	dst[px ] = (sRA + dRA - sRA*dRA) * demultiply;
	dst[px+1] = (sGA + dGA - sGA*dGA) * demultiply;
	dst[px+2] = (sBA + dBA - sBA*dBA) * demultiply;
	break;
	
	case 'multiply':
	dst[px ] = (sRA*dRA + sRA*(1-dA) + dRA*(1-sA)) * demultiply;
	dst[px+1] = (sGA*dGA + sGA*(1-dA) + dGA*(1-sA)) * demultiply;
	dst[px+2] = (sBA*dBA + sBA*(1-dA) + dBA*(1-sA)) * demultiply;
	break;
	
	case 'difference':
	dst[px ] = (sRA + dRA - 2 * Math.min( sRA*dA, dRA*sA )) * demultiply;
	dst[px+1] = (sGA + dGA - 2 * Math.min( sGA*dA, dGA*sA )) * demultiply;
	dst[px+2] = (sBA + dBA - 2 * Math.min( sBA*dA, dBA*sA )) * demultiply;
	break;
	
	// ******* Slightly different from Photoshop, where alpha is concerned
	case 'src-in':
	// Only differs from Photoshop in low-opacity areas
	dA2 = sA*dA;
	demultiply = 255 / dA2;
	dst[px+3] = dA2*255;
	dst[px ] = sRA*dA * demultiply;
	dst[px+1] = sGA*dA * demultiply;
	dst[px+2] = sBA*dA * demultiply;
	break;
	
	case 'plus':
	case 'add':
	// Photoshop doesn't simply add the alpha channels; this might be correct wrt SVG 1.2
	dA2 = Math.min(1,sA+dA);
	dst[px+3] = dA2*255;
	demultiply = 255 / dA2;
	dst[px ] = Math.min(sRA + dRA,1) * demultiply;
	dst[px+1] = Math.min(sGA + dGA,1) * demultiply;
	dst[px+2] = Math.min(sBA + dBA,1) * demultiply;
	break;
	
	case 'overlay':
	// Correct for 100% opacity case; colors get clipped as opacity falls
	dst[px ] = (dRA<=0.5) ? (2*src[px ]*dRA/dA) : 255 - (2 - 2*dRA/dA) * (255-src[px ]);
	dst[px+1] = (dGA<=0.5) ? (2*src[px+1]*dGA/dA) : 255 - (2 - 2*dGA/dA) * (255-src[px+1]);
	dst[px+2] = (dBA<=0.5) ? (2*src[px+2]*dBA/dA) : 255 - (2 - 2*dBA/dA) * (255-src[px+2]);
	
	// http://dunnbypaul.net/blends/
	// dst[px ] = ( (dRA<=0.5) ? (2*sRA*dRA) : 1 - (1 - 2*(dRA-0.5)) * (1-sRA) ) * demultiply;
	// dst[px+1] = ( (dGA<=0.5) ? (2*sGA*dGA) : 1 - (1 - 2*(dGA-0.5)) * (1-sGA) ) * demultiply;
	// dst[px+2] = ( (dBA<=0.5) ? (2*sBA*dBA) : 1 - (1 - 2*(dBA-0.5)) * (1-sBA) ) * demultiply;
	
	// http://www.barbato.us/2010/12/01/blimageblending-emulating-photoshops-blending-modes-opencv/#toc-blendoverlay
	// dst[px ] = ( (sRA<=0.5) ? (sRA*dRA + sRA*(1-dA) + dRA*(1-sA)) : (sRA + dRA - sRA*dRA) ) * demultiply;
	// dst[px+1] = ( (sGA<=0.5) ? (sGA*dGA + sGA*(1-dA) + dGA*(1-sA)) : (sGA + dGA - sGA*dGA) ) * demultiply;
	// dst[px+2] = ( (sBA<=0.5) ? (sBA*dBA + sBA*(1-dA) + dBA*(1-sA)) : (sBA + dBA - sBA*dBA) ) * demultiply;
	
	// http://www.nathanm.com/photoshop-blending-math/
	// dst[px ] = ( (sRA < 0.5) ? (2 * dRA * sRA) : (1 - 2 * (1 - sRA) * (1 - dRA)) ) * demultiply;
	// dst[px+1] = ( (sGA < 0.5) ? (2 * dGA * sGA) : (1 - 2 * (1 - sGA) * (1 - dGA)) ) * demultiply;
	// dst[px+2] = ( (sBA < 0.5) ? (2 * dBA * sBA) : (1 - 2 * (1 - sBA) * (1 - dBA)) ) * demultiply;
	break;
	
	case 'hardlight':
	dst[px ] = (sRA<=0.5) ? (2*dst[px ]*sRA/dA) : 255 - (2 - 2*sRA/sA) * (255-dst[px ]);
	dst[px+1] = (sGA<=0.5) ? (2*dst[px+1]*sGA/dA) : 255 - (2 - 2*sGA/sA) * (255-dst[px+1]);
	dst[px+2] = (sBA<=0.5) ? (2*dst[px+2]*sBA/dA) : 255 - (2 - 2*sBA/sA) * (255-dst[px+2]);
	break;
	
	case 'colordodge':
	case 'dodge':
	if ( src[px ] == 255 && dRA==0) dst[px ] = 255;
	else dst[px ] = Math.min(255, dst[px ]/(255 - src[px ])) * demultiply;
	
	if ( src[px+1] == 255 && dGA==0) dst[px+1] = 255;
	else dst[px+1] = Math.min(255, dst[px+1]/(255 - src[px+1])) * demultiply;
	
	if ( src[px+2] == 255 && dBA==0) dst[px+2] = 255;
	else dst[px+2] = Math.min(255, dst[px+2]/(255 - src[px+2])) * demultiply;
	break;
	
	case 'colorburn':
	case 'burn':
	if ( src[px ] == 0 && dRA==0) dst[px ] = 0;
	else dst[px ] = (1 - Math.min(1, (1 - dRA)/sRA)) * demultiply;
	
	if ( src[px+1] == 0 && dGA==0) dst[px+1] = 0;
	else dst[px+1] = (1 - Math.min(1, (1 - dGA)/sGA)) * demultiply;
	
	if ( src[px+2] == 0 && dBA==0) dst[px+2] = 0;
	else dst[px+2] = (1 - Math.min(1, (1 - dBA)/sBA)) * demultiply;
	break;
	
	case 'darken':
	case 'darker':
	dst[px ] = (sRA>dRA ? dRA : sRA) * demultiply;
	dst[px+1] = (sGA>dGA ? dGA : sGA) * demultiply;
	dst[px+2] = (sBA>dBA ? dBA : sBA) * demultiply;
	break;
	
	case 'lighten':
	case 'lighter':
	dst[px ] = (sRA<dRA ? dRA : sRA) * demultiply;
	dst[px+1] = (sGA<dGA ? dGA : sGA) * demultiply;
	dst[px+2] = (sBA<dBA ? dBA : sBA) * demultiply;
	break;
	
	case 'exclusion':
	dst[px ] = (dRA+sRA - 2*dRA*sRA) * demultiply;
	dst[px+1] = (dGA+sGA - 2*dGA*sGA) * demultiply;
	dst[px+2] = (dBA+sBA - 2*dBA*sBA) * demultiply;
	break;
	
	// ******* UNSUPPORTED
	default:
	dst[px] = dst[px+3] = 255;
	dst[px+1] = px%8==0 ? 255 : 0;
	dst[px+2] = px%8==0 ? 0 : 255;
	}
	}
	destContext.putImageData(dstD,offsets.destX,offsets.destY);
	};
	// For querying of functionality from other libraries
	var modes = CanvasRenderingContext2D.prototype.blendOnto.supportedBlendModes = 'normal src-over screen multiply difference src-in plus add overlay hardlight colordodge dodge colorburn burn darken lighten exclusion'.split(' ');
	var supports = CanvasRenderingContext2D.prototype.blendOnto.supports = {};
	for (var i=0,len=modes.length;i<len;++i) supports[modes[i]] = true;
}