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GLSTENCILFUNC(3G)		 OpenGL Manual		     GLSTENCILFUNC(3G)

NAME
       glStencilFunc - set front and back function and reference value for
       stencil testing

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

PARAMETERS
       func
	   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.

       ref
	   Specifies the reference value for the stencil test.	ref is clamped
	   to the range 0 2 n - 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. Stencil planes are first drawn into using GL drawing
       primitives, then geometry and images are rendered 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() or
       glStencilOpSeparate().

       There can be two separate sets of func, ref, and mask parameters; one
       affects back-facing polygons, and the other affects front-facing
       polygons as well as other non-polygon primitives.  glStencilFunc() sets
       both front and back stencil state to the same values. Use
       glStencilFuncSeparate() to set front and back stencil state to
       different values.

       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 2 n - 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 2 n - 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.

       glStencilFunc() is the same as calling glStencilFuncSeparate() with
       face set to GL_FRONT_AND_BACK.

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

ASSOCIATED GETS
       glGet() with argument GL_STENCIL_FUNC, GL_STENCIL_VALUE_MASK,
       GL_STENCIL_REF, GL_STENCIL_BACK_FUNC, GL_STENCIL_BACK_VALUE_MASK,
       GL_STENCIL_BACK_REF, or GL_STENCIL_BITS

       glIsEnabled() with argument GL_STENCIL_TEST

SEE ALSO
       glBlendFunc(), glDepthFunc(), glEnable(), glLogicOp(),
       glStencilFuncSeparate(), glStencilMask(), glStencilMaskSeparate(),
       glStencilOp(), glStencilOpSeparate()

COPYRIGHT
       Copyright © 1991-2006 Silicon Graphics, Inc. This document is licensed
       under the SGI Free Software B License. For details, see
       http://oss.sgi.com/projects/FreeB/.

AUTHORS
       opengl.org

opengl.org			  03/16/2013		     GLSTENCILFUNC(3G)
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