New function to threshold a pixbuf's alpha channel into a bitmap.

New function to threshold a pixbuf's alpha channel into a bitmap.

1999-10-27  Federico Mena Quintero  <federico@redhat.com>

	* src/gdk-pixbuf-render.c (gdk_pixbuf_render_threshold_alpha): New
	function to threshold a pixbuf's alpha channel into a bitmap.

	* src/gdk-pixbuf.c (gdk_pixbuf_new): Fixed so that it will
	contemplate future extensions to ArtPixBuf's formats.

	* src/io-png.c (png_info_callback): Use the new API of gdk_pixbuf_new().

	* src/gdk-pixbuf.h (gdk_pixbuf_get_height): Added some convenience
	macros to fetch the ArtPixBuf's fields.