pixmap.return
and mask.return arguments, respectively, and renders a pixbuf and its
corresponding tresholded alpha mask to them. This is merely a convenience
function; applications that need to render pixbufs with dither offsets or to
given drawables should use gdkDrawPixbuf, and gdkPixbufRenderThresholdAlpha.gdkPixbufRenderPixmapAndMaskForColormap(object, colormap, alpha.threshold = 127)colormap.
This colormap must match the colormap of the window where the pixmap
will eventually be used or an error will result.
If the pixbuf does not have an alpha channel, then *mask.return will be set
to NULL.