always pass
pass if the incoming value equals the the depth buffer value
pass if the incoming value is greater than or equal to the depth buffer value
pass if the incoming value is greater than the depth buffer value
pass if the incoming value is less than or equal to the depth buffer value
pass if the incoming value is less than the depth buffer value
never pass
pass if the incoming value is not equal to the depth buffer value
An enumeration specifying the depth comparison function, which sets the conditions under which the pixel will be drawn. The default value is LESS.