I am trying to achieve a transparent rectangle in the resulting frame rendered on screen, but cannot find how to do this.
Pipeline: I am writing a c++ application. I have multiple incoming video streams composed into one frame using compositor, rendered on screen using kmssink. (something like udpsrc -> rtpdepay -> decoder -(multiple)> compositor -> videoconvert -> kmssink)
Background: The setup is that different applications render on different DRM devices (devices are mapped to their own z-ordered layer on display, merged together by hardware). I need to sometimes make "my layer" transparent in a rectangle to show part of the layer below mine. I am new to gstreamer and "graphics" in general - perhaps this is a trivial task for the experienced person.
