I have found a solution that kind of does the job, although takes three times as much memory. Every update I calculate the difference between the new and the old saturation matrix, this eliminates 60% of the nonzero values, which means it gets drawn that much faster. As a second layer of optimization I call repaint with a rectangle describing the most important zone, and call update every 60ms.

@SGaist Hi, I'm running Windows 10, OpenGL 4.5.0