This adds API to let you override the choice of Cogl's winsys backend.
Previously it was only possible to override the winsys using the
COGL_RENDERER environment variable, but it's useful for something like
Clutter to be able to control the winsys via API without needing
environment variable tricks. This also adds API to query back the
winsys chosen by Cogl, in case you don't set an explicit override.
Signed-off-by: Neil Roberts <neil@linux.intel.com>
All of the winsys backends didn't handle cleaning up the CoglOnscreen
properly so that they would assert in cogl_onscreen_free because the
winsys pointer is never freed. They also didn't cope if deinit is
called before init (which will be the case if an onscreen is created
and freed without being allocated).
When SetPixelFormat fails, the DC would get released but none of the
other resources would be freed. This patch makes it call
_cogl_winsys_onscreen_deinit on failure to clean up all of the
resources. The patch looks big because it moves the onscreen_deinit
and onscreen_bind functions.
