[cairo] enumeration of backends

[Øyvind Kolås]

In GtkCairo it is currently possible to select glitz as the rendering
backend by setting the GTKCAIRO_GL enviroment variable to a non 0 value.

This enviroment variable is internally reflected as the gtkcairo->gl
variable. As I see it this is a less than ideal situation, but it works
when the backend selection actually is boolean.

A more ideal situation would be to have a enumeration value, where each
backend has a constant value. This is something a 'autoselect' backend,
or other libraries / applications supporting multiple backends also
need.

Is this something that belongs in cairo.h ?

 typedef enum cairo_backend {
    CAIRO_IMAGE_BACKEND,
    CAIRO_XLIB_BACKEND,
    CAIRO_XCB_BACKEND
    CAIRO_GL_BACKEND,
    CAIRO_PNG_BACKEND,
    CAIRO_PS_BACKEND,
    CAIRO_PDF_BACKEND
 } cairo_backend_t;

 another thing that would be useful, is choosing which backend actually
 feeds the image backend, and thus the png backend, this could be used
 to hardware accelerate creation of png images on a webserver.

/Øyvind K.

-- 
  .^.
  /V\    Øyvind Kolås,  Gjøvik University College, Norway 
 /(_)\   <oeyvindk at hig.no>,<pippin at users.sourceforge.net>
  ^ ^