OpenGL Programming Guide

Chapter 3Viewing

Viewport Transformation

The Transformed z Coordinate

The z or depth coordinate is encoded and then stored during the viewport transformation. You can scale z values to lie within a desired range with the glDepthRange() command. (Chapter 10 discusses the depth buffer and the corresponding uses for the z coordinate.) Unlike x and y window coordinates, z window coordinates are treated by OpenGL as though they always range from 0.0 to 1.0. void glDepthRange(GLclampd near, GLclampd far);

Defines an encoding for z coordinates that's performed during the viewport transformation. The near and far values represent adjustments to the minimum and maximum values that can be stored in the depth buffer. By default, they're 0.0 and 1.0, respectively, which work for most applications. These parameters are clamped to lie within [0,1].

OpenGL Programming Guide