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GLSTENCILOPSEPARATE(3G)                          OpenGL 3.3                          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 (C) 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/.



OpenGL 3.3                                       03/08/2011                          GLSTENCILOPSEPARATE(3G)