man glDepthFunc (3): specify the value used for depth buffer comparisons

C SPECIFICATION

void glDepthFunc(GLenum func);

PARAMETERS

func

: Specifies the depth comparison function. Symbolic constants GL_NEVER, GL_LESS, GL_EQUAL, GL_LEQUAL, GL_GREATER, GL_NOTEQUAL, GL_GEQUAL, and GL_ALWAYS are accepted. The initial value is GL_LESS.

DESCRIPTION

glDepthFunc specifies the function used to compare each incoming pixel depth value with the depth value present in the depth buffer. The comparison is performed only if depth testing is enabled. (See glEnable() and glDisable() of GL_DEPTH_TEST.)

func specifies the conditions under which the pixel will be drawn. The comparison functions are as follows:

GL_NEVER

: Never passes.

GL_LESS

: Passes if the incoming depth value is less than the stored depth value.

GL_EQUAL

: Passes if the incoming depth value is equal to the stored depth value.

GL_LEQUAL

: Passes if the incoming depth value is less than or equal to the stored depth value.

GL_GREATER

: Passes if the incoming depth value is greater than the stored depth value.

GL_NOTEQUAL

: Passes if the incoming depth value is not equal to the stored depth value.

GL_GEQUAL

: Passes if the incoming depth value is greater than or equal to the stored depth value.

GL_ALWAYS

: Always passes.

The initial value of func is GL_LESS. Initially, depth testing is disabled. If depth testing is disabled or if no depth buffer exists, it is as if the depth test always passes.

NOTES

Even if the depth buffer exists and the depth mask is non-zero, the depth buffer is not updated if the depth test is disabled. In order to unconditionally write to the depth buffer, the depth test should be enabled and set to GL_ALWAYS.

ERRORS

GL_INVALID_ENUM is generated if func is not an accepted value.

ASSOCIATED GETS

glGet() with argument GL_DEPTH_FUNC

glIsEnabled() with argument GL_DEPTH_TEST