Using the Z-Buffer

In order to turn on the Z-buffer, you must call

glEnable(GL_DEPTH_TEST)

To disable Z-Buffering, call

glDisable(GL_DEPTH_TEST)

Z-Buffer and the Freedoms

Curiously, turning on Z-buffering allows the Freedoms to perform much faster than with it off. This is because when Z-buffering is on, OpenGL allows the system to draw primitives in any order it wants, and not in the order the user specified them. This liberty allows the Freedoms to distribute primitive drawing among its processors, providing much better performance.