Don't erase background for visual trace in Quartz Composer

Question

I it possible NOT to clear the background in Quartz Composer? I want to move an image across the screen and keep it visible at the old positions to have some sort of trace effect.

Thanks and regards,
Sebastian Mecklenburg

Answer 1

Do your rendering inside a Render In Image patch, and connect its output to an Addition patch. Connect the output of Addition to an Accumulator patch, and connect the output of the Accumulator patch to the "Background Image" port of the Addition patch, to create a feedback loop. Then connect the Addition patch to a Billboard.