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GLSTENCILOP(3G) 			  OpenGL Manual 			  GLSTENCILOP(3G)

NAME
       glStencilOp - set front and back stencil test actions

C SPECIFICATION
       void glStencilOp(GLenum sfail, GLenum dpfail, GLenum dppass);

PARAMETERS
       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. Use glStencilOpSeparate() to set front and back stencil state to different values.

       glStencilOp 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 glStencilOp 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 tests always pass, regardless of any
       call to glStencilOp.

       glStencilOp() is the same as calling glStencilOpSeparate() with face set to
       GL_FRONT_AND_BACK.

ERRORS
       GL_INVALID_ENUM is generated if sfail, dpfail, or dppass is any value other than the
       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(), glStencilOpSeparate()

COPYRIGHT
       Copyright (C) 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				    06/10/2014				  GLSTENCILOP(3G)
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