The app could request access to the user's Apple Pay activity. The user would have to grant the access. I don't see a "privacy" breach...

Thank you Eugene, I will start by implementing a CoreGraphics mockup and see how it goes. Two buffers seems indeed the minimum to guaranty immutability. The bandwidth is USB 2.0 bandwidth and I assume it will be enough to drive the LCD since the manufacturer does it already with its own software. You said "drawables" in your answer which leads me to think you have a Metal API background, if it is the case, do you think Metal would be any improvement over CG in this case where I'm dealing with 2D only? Can Metal pipeline be set to not render to screen but into a buffer? Best regards, Thierry