Ok, I prepared a patch explaining the problem I’m trying to solve (my original project is to complicated and containing to many external dependences to post it).
In posted patch I located two [jit.gl.videoplane] objects. One filled with an image taken from [jit.grab], second one containing stuff from [jit.mgraphics]. I’m using @layer parameter to put the [jit.gl.videoplane] containing data from [jit.mgraphics] "over" the [jit.gl.videoplane] with [jit.grab] data. Moreover I’m using alphablending for both [jit.gl.videoplane]’s.
Now I need a method to change "paint" command used for [jit.mgraphics] to something allowing me to create clear (filled with 0.) alpha channel for the image produced by [jit.mgraphics] – and see both: the drawings from [jit.mgraphics] and background from [jit.grab].
Maybe a good model of the thing, I want to create is "HUD" display.