This change has two effects:
1. Only calls FlushCallbacks when we're actually flushing data to a
client. The unnecessary FlushCallback calls could cause significant
performance degradation with compositing, which is significantly
reduced even without any driver changes.
2. By passing the ClientPtr to FlushCallbacks, drivers can completely
eliminate unnecessary flushing of GPU commands by keeping track of
whether we're flushing any XDamageNotify events to the client for
which the corresponding rendering commands haven't been flushed to
the GPU yet.
Reviewed-by: Adam Jackson <ajax@redha.com>
Signed-off-by: Michel Dänzer <michel.daenzer@amd.com>