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GLSTENCILOPSEPARATE(3G)		 OpenGL Manual	       GLSTENCILOPSEPARATE(3G)

NAME
       glStencilOpSeparate - set front and/or back stencil test actions

C SPECIFICATION
       void glStencilOpSeparate(GLenum face, GLenum sfail, GLenum dpfail,
				GLenum dppass);

PARAMETERS
       face
	   Specifies whether front and/or back stencil state is updated. Three
	   symbolic constants are valid: GL_FRONT, GL_BACK, and
	   GL_FRONT_AND_BACK.

       sfail
	   Specifies the action to take when the stencil test fails. Eight
	   symbolic constants are accepted: GL_KEEP, GL_ZERO, GL_REPLACE,
	   GL_INCR, GL_INCR_WRAP, GL_DECR, GL_DECR_WRAP, and GL_INVERT. The
	   initial value is GL_KEEP.

       dpfail
	   Specifies the stencil action when the stencil test passes, but the
	   depth test fails.  dpfail accepts the same symbolic constants as
	   sfail. The initial value is GL_KEEP.

       dppass
	   Specifies the stencil action when both the stencil test and the
	   depth test pass, or when the stencil test passes and either there
	   is no depth buffer or depth testing is not enabled.	dppass accepts
	   the same symbolic constants as sfail. The initial value is GL_KEEP.

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 value in the stencil buffer and a reference
       value. To enable and disable the test, call glEnable() and glDisable()
       with argument GL_STENCIL_TEST; to control it, call glStencilFunc() or
       glStencilFuncSeparate().

       There can be two separate sets of sfail, dpfail, and dppass parameters;
       one affects back-facing polygons, and the other affects front-facing
       polygons as well as other non-polygon primitives.  glStencilOp() sets
       both front and back stencil state to the same values, as if
       glStencilOpSeparate() were called with face set to GL_FRONT_AND_BACK.

       glStencilOpSeparate takes three arguments that indicate what happens to
       the stored stencil value while stenciling is enabled. If the stencil
       test fails, no change is made to the pixel's color or depth buffers,
       and sfail specifies what happens to the stencil buffer contents. The
       following eight actions are possible.

       GL_KEEP
	   Keeps the current value.

       GL_ZERO
	   Sets the stencil buffer value to 0.

       GL_REPLACE
	   Sets the stencil buffer value to ref, as specified by
	   glStencilFunc().

       GL_INCR
	   Increments the current stencil buffer value. Clamps to the maximum
	   representable unsigned value.

       GL_INCR_WRAP
	   Increments the current stencil buffer value. Wraps stencil buffer
	   value to zero when incrementing the maximum representable unsigned
	   value.

       GL_DECR
	   Decrements the current stencil buffer value. Clamps to 0.

       GL_DECR_WRAP
	   Decrements the current stencil buffer value. Wraps stencil buffer
	   value to the maximum representable unsigned value when decrementing
	   a stencil buffer value of zero.

       GL_INVERT
	   Bitwise inverts the current stencil buffer value.

       Stencil buffer values are treated as unsigned integers. When
       incremented and decremented, values are clamped to 0 and 2 n - 1, where
       n is the value returned by querying GL_STENCIL_BITS.

       The other two arguments to glStencilOpSeparate specify stencil buffer
       actions that depend on whether subsequent depth buffer tests succeed
       (dppass) or fail (dpfail) (see glDepthFunc()). The actions are
       specified using the same eight symbolic constants as sfail. Note that
       dpfail is ignored when there is no depth buffer, or when the depth
       buffer is not enabled. In these cases, sfail and dppass specify stencil
       action when the stencil test fails and passes, respectively.

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 face is any value other than GL_FRONT,
       GL_BACK, or GL_FRONT_AND_BACK.

       GL_INVALID_ENUM is generated if sfail, dpfail, or dppass is any value
       other than the eight defined constant values.

ASSOCIATED GETS
       glGet() with argument GL_STENCIL_FAIL, GL_STENCIL_PASS_DEPTH_PASS,
       GL_STENCIL_PASS_DEPTH_FAIL, GL_STENCIL_BACK_FAIL,
       GL_STENCIL_BACK_PASS_DEPTH_PASS, GL_STENCIL_BACK_PASS_DEPTH_FAIL, or
       GL_STENCIL_BITS

       glIsEnabled() with argument GL_STENCIL_TEST

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

COPYRIGHT
       Copyright © 2006 Khronos Group. This material may be distributed
       subject to the terms and conditions set forth in the Open Publication
       License, v 1.0, 8 June 1999.  http://opencontent.org/openpub/.

AUTHORS
       opengl.org

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