How to redraw only a portion of the presenting framebuffer?

Question

I want to implement a simple paint feature on iOS. I have some framebuffers/textures wired up to get the desired final composition.

Redrawing the whole screen is a huge overhead. I can determine a rectangle that has changed.

So what is the best way to draw only that portion?

Answer 1

glScissor(0, 0, 50, 50); glEnable(GL_SCISSOR_TEST);