This will also cause clearing to 0,0,0,0.
Essential in order to allow fast testing of window transparency
issues in combination with QRhi and the various backends.
Change-Id: Iee2763c1d06f1d3e5d59a9142abaf30fab1dc543
Reviewed-by: Christian Strømme <christian.stromme@qt.io>
D3D11 and GL (4.3+, ES 3.1+) will come separately at a
later time.
Change-Id: If30f2f3d062fa27e57e9912674669225b82a7b93
Reviewed-by: Lars Knoll <lars.knoll@qt.io>