Instead of having separate callbacks for each backend-handled feature
(like MPGLContext.fullscreen, MPGLContext.border, etc.), pass the
VOCTRL responsible for this directly to the backend. This allows
removing a bunch of callbacks, that currently must be set even for
optional/lesser features (like VOCTRL_BORDER).
This requires changes to all VOs using gl_common, as well as all
backends that support gl_common.
Also introduce VOCTRL_CHECK_EVENTS. vo.check_events is now optional.
VO backends can use VOCTRL_CHECK_EVENTS instead to implementing
check_events. This has the advantage that the event handling code in
VOs doesn't have to be duplicated if vo_control() is used.
Allows playing video with alpha information on X11, as long as the video
contains alpha and the window manager does compositing. See vo.rst.
Whether a window can be transparent is decided by the choice of the X
Visual used for window creation. Unfortunately, there's no direct way to
request such a Visual through the GLX or the X API, and use of the
XRender extension is required to find out whether a Visual implies a
framebuffer with alpha used by XRender (see for example [1]). Instead of
depending on the XRender wrapper library (which would require annoying
configure checks, even though XRender is virtually always supported),
use a simple heuristics to find out whether a Visual has alpha. Since
getting it wrong just means an optional feature will not work as
expected, we consider this ok.
[1] http://stackoverflow.com/questions/4052940/how-to-make-an-opengl-rendering-context-with-transparent-background/9215724#9215724
Do this instead of stuffing all x11/cocoa/win32/wayland specific code
into gl_common.c. The cocoa specific parts could probably go directly
into cocoa_common.m, possibly same with wayland.
Also redo how the list of backends is managed. Get rid of the GLTYPE_
constants. Instead of having a big switch() on GLTYPE_, each backend
entry has a function pointer to setup the MPGLContext callback (e.g.
mpgl_set_backend_x11()).
wm4