void render_to_drawable_alpha(GdkWindow
drawable, int
src_x, int
src_y, int
dest_x, int
dest_y, int
width, int
height, GdkPixbufAlphaMode
alpha_mode, int
alpha_threshold [, GdkRgbDither
dither = Gdk::RGB_DITHER_NORMAL [, int
x_dither = Gdk::RGB_DITHER_NORMAL [, int
y_dither = Gdk::RGB_DITHER_NORMAL]]]);