Make sure the frame callbacks are sent at the right time

When there is a rendering thread, like with QtQuick compositors,
there is a race condition where the frame callbacks are sent before
the last buffer the client sent is released.
Assume the following scenario:
attach(B1)/frame(F1)/commit()...frame started...attach(B2)/frame(F2)/
commit()...frame finished.
On frame finished the callback just installed is emitted before the
buffer B2 is being used and B1 released. That forces the client to
allocate a third buffer to draw the next frame.
Now, do not send out the frame callbacks until a new frame started.
The successive draw will release B1, use the new B2 and than send out F2.

Change-Id: I5743c7baf9fdd3cde28c5f594ff646c06abb74b7
Reviewed-by: Gunnar Sletta <gunnar.sletta@jollamobile.com>
Reviewed-by: Jørgen Lind <jorgen.lind@digia.com>

1 files changed, 1 insertions, 0 deletions

diff --git a/src/compositor/compositor_api/qwaylandcompositor.h b/src/compositor/compositor_api/qwaylandcompositor.h
index 6ed9cd894..9009f4caa 100644
--- a/src/compositor/compositor_api/qwaylandcompositor.h
+++ b/src/compositor/compositor_api/qwaylandcompositor.h
@@ -84,6 +84,7 @@ public:
 
     struct wl_display *waylandDisplay() const;
 
+    void frameStarted();
     void sendFrameCallbacks(QList<QWaylandSurface *> visibleSurfaces);
 
     void destroyClientForSurface(QWaylandSurface *surface);