Specifies whether front and/or back stencil state is updated. Three symbolic constants are valid: GL_FRONT , GL_BACK , and GL_FRONT_AND_BACK .
Specifies the test function. Eight symbolic constants are valid: GL_NEVER , GL_LESS , GL_LEQUAL , GL_GREATER , GL_GEQUAL , GL_EQUAL , GL_NOTEQUAL , and GL_ALWAYS . The initial value is GL_ALWAYS .
Specifies the reference value for the stencil test. ref is clamped to the range , where is the number of bitplanes in the stencil buffer. The initial value is 0.
Specifies a mask that is ANDed with both the reference value and the stored stencil value when the test is done. The initial value is all 1's.