I faced with a problem when setting the local alpha blending.
Use 2 framebuffer:
fb0 for my qt application (widget with a black background and green text information);
fb1 for outputting a video camera using gstreamer 1.0
How to programmatically configure framebuffer on 32 bit?
P.S. Use this article to configure the global alpha blending, but when mixed are black pixels around the green text.