darker color

Caman.Blender.register("darkerColor", function (rgbaLayer, rgbaParent) {
			var LUMINANCE_WEIGHTING = [0.299, 0.587, 0.114];
			
			return (CanvasHelpers.intensity(rgbaLayer, LUMINANCE_WEIGHTING) < CanvasHelpers.intensity(rgbaParent, LUMINANCE_WEIGHTING)) 
						? CanvasHelpers.blend(rgbaParent, rgbaLayer) 
						: CanvasHelpers.blend(rgbaLayer, rgbaParent);
        });

static intensity(rgba, luminanceWeighting)
	{
		var frgba = CanvasHelpers.rsUnpackColor8888(rgba);
			
		var luminance = CanvasHelpers.dot(frgba, luminanceWeighting);
		var intensity = CanvasHelpers.clamp(luminance * 255, 0, 255);

		return Math.floor(intensity);
	}
	
static rsUnpackColor8888(rgba) {
        return {
            r: rgba.r / 255.0,
            g: rgba.g / 255.0,
            b: rgba.b / 255.0,
            a: rgba.a / 255.0
        };
    }
    
static clamp(x, min, max) {
		if (x < min) {
			return min;
		}
		if (x > max) {
			return max;
		}
		return x;
	}
	
static dot(frgba, luminanceWeighting)
	{		
		return frgba.r * luminanceWeighting[0] + 
			frgba.g * luminanceWeighting[1] + 
			frgba.b * luminanceWeighting[2];
	}

static blend(rgba1, rgba2) {
		return {
			r: rgba2.a > 0 ? CanvasHelpers.componentAlpha(rgba1.r, rgba2.r, rgba2.a / 255) : rgba1.r,
			g: rgba2.a > 0 ? CanvasHelpers.componentAlpha(rgba1.g, rgba2.g, rgba2.a / 255) : rgba1.g,
			b: rgba2.a > 0 ? CanvasHelpers.componentAlpha(rgba1.b, rgba2.b, rgba2.a / 255) : rgba1.b,
			a: rgba2.a + rgba1.a * ((255 - rgba2.a) / 255)
		};
	}
	
static componentAlpha(c1, c2, opacity) {
        return Math.floor(opacity * c2 + (1 - opacity) * c1);
    }