This adds a callback that can be registered with
cogl_onscreen_add_dirty_callback which will get called whenever the
window system determines that the contents of the window is dirty and
needs to be redrawn. Under the two X-based winsys's, this is reported
off the back of the Expose events, under SDL it is reported from
SDL_VIDEOEXPOSE or SDL_WINDOWEVENT_EXPOSED and under Windows from the
WM_PAINT messages. The Wayland winsys doesn't really have the concept
of dirtying the buffer but in order to allow applications to work the
same way on all platforms it will emit the event when the surface is
first shown and whenever it is resized.
There is a private feature flag to specify whether dirty events are
supported. If the winsys does not set this then Cogl will simulate
dirty events by emitting one when the window is first allocated and
when it is resized. The only winsys's that don't set this flag are
things like KMS or the EGL null winsys where there is no windowing
system and showing and hiding the onscreen doesn't really make any
sense. In that case Cogl can assume the buffer will only become dirty
once when it is first allocated.
Reviewed-by: Robert Bragg <robert@linux.intel.com>
(cherry picked from commit 85c5a9ba419b2247bd768284c79ee69164a0c098)
Conflicts:
cogl/cogl-private.h
d0944b8fbd