OpenGL Programming Guide: The Official Guide to Learning OpenGL, Version 4.3, Eighth Edition

Advanced: z Precision

One bizarre effect of these transformations is z fighting. The hardware’s floating-point numbers used to do the computation have limited precision. Hence, depth coordinates that are mathematically distinct end up having the same (or even reversed) actual floating-point z values. This in turn causes incorrectly hidden objects in the depth buffer. The effect varies per pixel and can cause disturbing flickering intersections of nearby objects. Precision of z is made even worse with perspective division, which is applied to the depth coordinate along with all the other coordinates: As the transformed depth coordinate moves farther away from the near clipping plane, its location becomes increasingly less precise, as shown in ...