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     <STRONG>NAME</STRONG>
	  <STRONG>glStencilFunc</STRONG>	- set function and reference value for stencil
	  testing


     <STRONG>C</STRONG> <STRONG>SPECIFICATION</STRONG>
	  void <STRONG>glStencilFunc</STRONG>( GLenum <EM>func</EM>,
			      GLint <EM>ref</EM>,
			      GLuint <EM>mask</EM> )


     <STRONG>PARAMETERS</STRONG>
	  <EM>func</EM>	Specifies the test function.  Eight tokens are valid:
		<STRONG>GL_NEVER</STRONG>, <STRONG>GL_LESS</STRONG>, <STRONG>GL_LEQUAL</STRONG>, <STRONG>GL_GREATER</STRONG>, <STRONG>GL_GEQUAL</STRONG>,
		<STRONG>GL_EQUAL</STRONG>, <STRONG>GL_NOTEQUAL</STRONG>, and <STRONG>GL_ALWAYS</STRONG>. The initial
		value is <STRONG>GL_ALWAYS</STRONG>.

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

	  <EM>mask</EM>	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.

     <STRONG>DESCRIPTION</STRONG>
	  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 <STRONG>glEnable</STRONG> and <STRONG>glDisable</STRONG> with argument
	  <STRONG>GL_STENCIL_TEST</STRONG>.  To specify actions based on	the outcome of
	  the stencil test, call <STRONG>glStencilOp</STRONG>.

	  <EM>func</EM> is a symbolic constant that determines the stencil
	  comparison function.	It accepts one of eight	values,	shown
	  in the following list.  <EM>ref</EM> 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.  <EM>mask</EM> is bitwise ANDed with both the
	  reference value and the stored stencil value,	with the ANDed
	  values participating in the comparison.

	  If <EM>stencil</EM> 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 <EM>func</EM>.
	  Only if the comparison succeeds is the pixel passed through
	  to the next stage in the rasterization process (see
	  <STRONG>glStencilOp</STRONG>).	 All tests treat <EM>stencil</EM> 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 <EM>func</EM>:

	  <STRONG>GL_NEVER</STRONG>	    Always fails.

	  <STRONG>GL_LESS</STRONG>	    Passes if (	<EM>ref</EM> &amp; <EM>mask</EM> ) &lt; ( <EM>stencil</EM> &amp;
			    <EM>mask</EM> ).

	  <STRONG>GL_LEQUAL</STRONG>	    Passes if (	<EM>ref</EM> &amp; <EM>mask</EM> ) <EM>&lt;</EM> ( <EM>stencil</EM> &amp;
			    <EM>mask</EM> ).

	  <STRONG>GL_GREATER</STRONG>	    Passes if (	<EM>ref</EM> &amp; <EM>mask</EM> ) &gt; ( <EM>stencil</EM> &amp;
			    <EM>mask</EM> ).

	  <STRONG>GL_GEQUAL</STRONG>	    Passes if (	<EM>ref</EM> &amp; <EM>mask</EM> ) <EM>&gt;</EM> ( <EM>stencil</EM> &amp;
			    <EM>mask</EM> ).

	  <STRONG>GL_EQUAL</STRONG>	    Passes if (	<EM>ref</EM> &amp; <EM>mask</EM> ) = ( <EM>stencil</EM> &amp;
			    <EM>mask</EM> ).

	  <STRONG>GL_NOTEQUAL</STRONG>	    Passes if (	<EM>ref</EM> &amp; <EM>mask</EM> ) <STRONG>/</STRONG>	( <EM>stencil</EM> &amp;
			    <EM>mask</EM> ).

	  <STRONG>GL_ALWAYS</STRONG>	    Always passes.

     <STRONG>NOTES</STRONG>
	  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.

     <STRONG>ERRORS</STRONG>
	  <STRONG>GL_INVALID_ENUM</STRONG> is generated if <EM>func</EM> is not one of the eight
	  accepted values.

	  <STRONG>GL_INVALID_OPERATION</STRONG> is generated if <STRONG>glStencilFunc</STRONG> is
	  executed between the execution of <STRONG>glBegin</STRONG> and	the
	  corresponding	execution of <STRONG>glEnd</STRONG>.

     <STRONG>ASSOCIATED</STRONG>	<STRONG>GETS</STRONG>
	  <STRONG>glGet</STRONG>	with argument <STRONG>GL_STENCIL_FUNC</STRONG>
	  <STRONG>glGet</STRONG>	with argument <STRONG>GL_STENCIL_VALUE_MASK</STRONG>
	  <STRONG>glGet</STRONG>	with argument <STRONG>GL_STENCIL_REF</STRONG>
	  <STRONG>glGet</STRONG>	with argument <STRONG>GL_STENCIL_BITS</STRONG>
	  <STRONG>glIsEnabled</STRONG> with argument <STRONG>GL_STENCIL_TEST</STRONG>

     <STRONG>SEE</STRONG> <STRONG>ALSO</STRONG>
	  <STRONG>glAlphaFunc</STRONG>, <STRONG>glBlendFunc</STRONG>, <STRONG>glDepthFunc</STRONG>, <STRONG>glEnable</STRONG>,
	  <STRONG>glIsEnabled</STRONG>, <STRONG>glLogicOp</STRONG>, <STRONG>glStencilOp</STRONG>

















































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