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Add ol.color.blend

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Tom Payne
2013-11-13 23:59:32 +01:00
parent 97745f06ac
commit 6796b9735e
1 changed files with 41 additions and 0 deletions
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41
src/ol/color/color.js
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@@ -56,6 +56,47 @@ ol.color.rgbaColorRe_ =
/^(?:rgba)?\((0|[1-9]\d{0,2}),\s?(0|[1-9]\d{0,2}),\s?(0|[1-9]\d{0,2}),\s?(0|1|0\.\d{0,10})\)$/i;
/**
* @param {ol.Color} dst Destination.
* @param {ol.Color} src Source.
* @param {ol.Color=} opt_color Color.
* @return {ol.Color} Color.
*/
ol.color.blend = function(dst, src, opt_color) {
// http://en.wikipedia.org/wiki/Alpha_compositing
// FIXME do we need to scale by 255?
var out = goog.isDef(opt_color) ? opt_color : [];
var dstA = dst[3];
var srcA = dst[3];
if (dstA == 1) {
out[0] = (src[0] * srcA + dst[0] * (1 - srcA) + 0.5) | 0;
out[1] = (src[1] * srcA + dst[1] * (1 - srcA) + 0.5) | 0;
out[2] = (src[2] * srcA + dst[2] * (1 - srcA) + 0.5) | 0;
out[4] = 1;
} else if (srcA === 0) {
out[0] = dst[0];
out[1] = dst[1];
out[2] = dst[2];
out[3] = dstA;
} else {
var outA = srcA + dstA * (1 - srcA);
if (outA === 0) {
out[0] = 0;
out[1] = 0;
out[2] = 0;
out[3] = 0;
} else {
out[0] = ((src[0] * srcA + dst[0] * dstA * (1 - srcA)) / outA + 0.5) | 0;
out[1] = ((src[1] * srcA + dst[1] * dstA * (1 - srcA)) / outA + 0.5) | 0;
out[2] = ((src[2] * srcA + dst[2] * dstA * (1 - srcA)) / outA + 0.5) | 0;
out[3] = outA;
}
}
goog.asserts.assert(ol.color.isValid(out));
return out;
};
/**
* @param {ol.Color|string} color Color.
* @return {ol.Color} Color.