NAME
	  glStencilFunc	- set function and reference value for stencil
	  testing


     C SPECIFICATION
	  void glStencilFunc( GLenum func,
			      GLint ref,
			      GLuint mask )


     PARAMETERS
	  func	Specifies the test function.  Eight tokens 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.

	  ref	Specifies the reference	value for the stencil test.
		ref is clamped to the range [0,2n-1], where n is the
		number of bitplanes in the stencil buffer. The initial
		value is 0.

	  mask	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.

     DESCRIPTION
	  Stenciling, like depth-buffering, enables and	disables
	  drawing on a per-pixel basis.	 You draw into the stencil
	  planes using GL drawing primitives, then render geometry and
	  images, using	the stencil planes to mask out portions	of the
	  screen.  Stenciling is typically used	in multipass rendering
	  algorithms to	achieve	special	effects, such as decals,
	  outlining, and constructive solid geometry rendering.

	  The stencil test conditionally eliminates a pixel based on
	  the outcome of a comparison between the reference value and
	  the value in the stencil buffer.  To enable and disable the
	  test,	call glEnable and glDisable with argument
	  GL_STENCIL_TEST.  To specify actions based on	the outcome of
	  the stencil test, call glStencilOp.

	  func is a symbolic constant that determines the stencil
	  comparison function.	It accepts one of eight	values,	shown
	  in the following list.  ref is an integer reference value
	  that is used in the stencil comparison.  It is clamped to
	  the range [0,2n-1], where n is the number of bitplanes in
	  the stencil buffer.  mask is bitwise ANDed with both the
	  reference value and the stored stencil value,	with the ANDed
	  values participating in the comparison.

	  If stencil represents	the value stored in the	corresponding
	  stencil buffer location, the following list shows the	effect
	  of each comparison function that can be specified by func.
	  Only if the comparison succeeds is the pixel passed through
	  to the next stage in the rasterization process (see
	  glStencilOp).	 All tests treat stencil values	as unsigned
	  integers in the range	[0,2n-1], where	n is the number	of
	  bitplanes in the stencil buffer.

	  The following	values are accepted by func:

	  GL_NEVER	    Always fails.

	  GL_LESS	    Passes if (	ref & mask ) < ( stencil &
			    mask ).

	  GL_LEQUAL	    Passes if (	ref & mask ) < ( stencil &
			    mask ).

	  GL_GREATER	    Passes if (	ref & mask ) > ( stencil &
			    mask ).

	  GL_GEQUAL	    Passes if (	ref & mask ) > ( stencil &
			    mask ).

	  GL_EQUAL	    Passes if (	ref & mask ) = ( stencil &
			    mask ).

	  GL_NOTEQUAL	    Passes if (	ref & mask ) /	( stencil &
			    mask ).

	  GL_ALWAYS	    Always passes.

     NOTES
	  Initially, the stencil test is disabled.  If there is	no
	  stencil buffer, no stencil modification can occur and	it is
	  as if	the stencil test always	passes.

     ERRORS
	  GL_INVALID_ENUM is generated if func is not one of the eight
	  accepted values.

	  GL_INVALID_OPERATION is generated if glStencilFunc is
	  executed between the execution of glBegin and	the
	  corresponding	execution of glEnd.

     ASSOCIATED	GETS
	  glGet	with argument GL_STENCIL_FUNC
	  glGet	with argument GL_STENCIL_VALUE_MASK
	  glGet	with argument GL_STENCIL_REF
	  glGet	with argument GL_STENCIL_BITS
	  glIsEnabled with argument GL_STENCIL_TEST

     SEE ALSO
	  glAlphaFunc, glBlendFunc, glDepthFunc, glEnable,
	  glIsEnabled, glLogicOp, glStencilOp