drawing.py 文件源码

def mix(fgcolor, bgcolor, mix_alpha):
    """ Creates a composite rgb of a foreground rgba and a background rgb.

         - fgcolor: an rgb of floats
         - bgcolor: an rgb of floats
         - mix_alpha: (0.0 - 1.0) the proportion of fgcolor mixed
                      into bgcolor
    """

    src_r, src_g, src_b = fgcolor.red, fgcolor.green, fgcolor.blue
    bg_r, bg_g, bg_b = bgcolor.red, bgcolor.green, bgcolor.blue

    # Source: http://en.wikipedia.org/wiki/Alpha_compositing
    r = ((1 - mix_alpha) * bg_r) + (mix_alpha * src_r)
    g = ((1 - mix_alpha) * bg_g) + (mix_alpha * src_g)
    b = ((1 - mix_alpha) * bg_b) + (mix_alpha * src_b)
    return Gdk.RGBA(red=r, green=g, blue=b)