[cairo] Image format independent API?

[DANIELLLANO]

Charles Wang wrote:
> I want to use cairo in embedded system which is leak of flash space, so
> I just want support one graphic format(such as png or jpeg). Now libsvg
> MUST support both of them without the modification of the code.
> 
> The attachment is a patch to configure.in and src/svg_image.c. If
> applied, configure will test libpng, libjpeg automatically and
> svg_image.c will include only the detected picture format.

Why is cairo exposing a image format dependent API instead exposing an
interface that's image format independent.
So instead having functions like:
cairo_png_surface_create
have format independent functions:
cairo_surface_create

It would be like gdk-pixbuf API for loading images.
Or maybe just using gdk-pixbuf.

(Forgiveme if the format independent API is already there I'm using
cairo releases only)