glDepthFunc

glDepthFunc is an OpenGL function that specifies the depth comparison function used during the depth test in fragment processing. The depth test compares the depth value of incoming fragments with the value stored in the depth buffer to determine visibility.

Prototype: void glDepthFunc(GLenum func). It sets the function used by the depth test for subsequent draw calls. When depth testing is enabled (glEnable(GL_DEPTH_TEST)), a fragment passes the depth test if the comparison against the corresponding depth buffer value evaluates to true; otherwise it is discarded.

Supported comparison functions include: GL_NEVER, GL_LESS, GL_EQUAL, GL_LEQUAL, GL_GREATER, GL_NOTEQUAL, GL_GEQUAL, GL_ALWAYS. For example, GL_LESS keeps fragments with a depth value strictly less than the current depth; GL_LEQUAL accepts equal depth values as well.

Default behavior is GL_LESS in most OpenGL contexts, meaning nearer fragments overwrite farther ones. Depth writes are controlled separately by glDepthMask; even when the test passes, depth values may or may not be written depending on the mask.

Notes: The depth buffer must be present and the depth test enabled for glDepthFunc to have an effect. Clearing the depth buffer with glClear(GL_DEPTH_BUFFER_BIT) and configuring the depth range influence results. glDepthFunc can be changed per program or per pass for techniques such as shadow mapping and multi-pass rendering.

See also glEnable, glDisable, GL_DEPTH_TEST, glDepthMask, glClear.