var Color = require(“../tree/color”),
functionRegistry = require("./function-registry");
// Color Blending // ref: www.w3.org/TR/compositing-1
function colorBlend(mode, color1, color2) {
var ab = color1.alpha, cb, // backdrop as = color2.alpha, cs, // source ar, cr, r = []; // result ar = as + ab * (1 - as); for (var i = 0; i < 3; i++) { cb = color1.rgb[i] / 255; cs = color2.rgb[i] / 255; cr = mode(cb, cs); if (ar) { cr = (as * cs + ab * (cb - as * (cb + cs - cr))) / ar; } r[i] = cr * 255; } return new Color(r, ar);
}
var colorBlendModeFunctions = {
multiply: function(cb, cs) { return cb * cs; }, screen: function(cb, cs) { return cb + cs - cb * cs; }, overlay: function(cb, cs) { cb *= 2; return (cb <= 1) ? colorBlendModeFunctions.multiply(cb, cs) : colorBlendModeFunctions.screen(cb - 1, cs); }, softlight: function(cb, cs) { var d = 1, e = cb; if (cs > 0.5) { e = 1; d = (cb > 0.25) ? Math.sqrt(cb) : ((16 * cb - 12) * cb + 4) * cb; } return cb - (1 - 2 * cs) * e * (d - cb); }, hardlight: function(cb, cs) { return colorBlendModeFunctions.overlay(cs, cb); }, difference: function(cb, cs) { return Math.abs(cb - cs); }, exclusion: function(cb, cs) { return cb + cs - 2 * cb * cs; }, // non-w3c functions: average: function(cb, cs) { return (cb + cs) / 2; }, negation: function(cb, cs) { return 1 - Math.abs(cb + cs - 1); }
};
for (var f in colorBlendModeFunctions) {
if (colorBlendModeFunctions.hasOwnProperty(f)) { colorBlend[f] = colorBlend.bind(null, colorBlendModeFunctions[f]); }
}
functionRegistry.addMultiple(colorBlend);