'This method sets the alpha value of the entire layer in a single
pass. This is helpful for merging layers with transparency.'

def setLayerAlpha(self, alpha):

    self._mSurface.set_alpha(alpha)
    pixels_alpha = pg.surfarray.pixels_alpha(self._mSurface)
    pixels_alpha[...] = (np.ones(pixels_alpha.shape) * alpha).astype(np.uint8)
    self._mAlphaDelta = (alpha / 255.0)
    del pixels_alpha
    return None
