cloudcover/context_blender.js at master · phl/cloudcover · GitHub

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
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
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
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;
}