OpenGL: How to clear only a part of the screen?

Question

Is it possible to not clear entire screen when using glClear() function? I need to clear only a part of the screen to save some rendering time, otherwise i would have to red

Answer 1

Draw a giant quad :) Apply this to just half your screen.

http://www.opengl.org/resources/faq/technical/transformations.htm#tran0090