As the title says... what does "OpenGL- Over" in the layer composition exactly do?
The wiki has no info about it and the tuts just say that we should use that without explaining why.
I'm asking because I made a couple of black and white pattern video files in Motion ( Prores 422, no alpha) and while having two layers on top of each other with layer 2 set to "OpenGL- Over" this layer shows layer 1 beneath it. I know this is expected behaviour, but I don't know why? Is it a preset luma key setting?