Always passes.
Passes if the fragment's depth value is equal to the value currently in the depth buffer.
Passes if the fragment's depth value greater than or equal to the value currently in the depth buffer.
Passes if the fragment's depth value is greater than the value currently in the depth buffer.
Passes if the fragment's depth value is less or equal to the value currently in the depth buffer.
Passes if the fragment's depth value is less than the value currently in the depth buffer.
Never passes.
Passes if the fragment's depth value is not equal to the value currently in the depth buffer.
When using depth testing one of these functions is used to compare the depth of an incoming fragment against the depth value currently stored in the depth buffer. The function is changed using
cogl_depth_state_set_test_function().The test is only done when depth testing is explicitly enabled. (See
cogl_depth_state_set_test_enabled())