Страницы справочника OS X

Эта страница руководства является частью версии 5.0 Инструментов XCode

Читать страницы руководства

GLSTENCILOP(3G)                                                                              GLSTENCILOP(3G)



NAME
       glStencilOp - set stencil test actions


C SPECIFICATION
       void glStencilOp( GLenum fail,
                         GLenum zfail,
                         GLenum zpass )


PARAMETERS
       fail   Specifies  the  action  to  take  when  the  stencil  test  fails.  Six symbolic constants are
              accepted: GL_KEEP, GL_ZERO, GL_REPLACE, GL_INCR, GL_DECR, and GL_INVERT. The initial value  is
              GL_KEEP.

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

       zpass  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.
              zpass accepts the same symbolic constants as fail. 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 algo-rithms algorithms
       rithms to achieve special effects, such as decals, outlining, and constructive solid geometry render-ing. rendering.
       ing.

       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.

       glStencilOp takes three arguments that indicate what happens to the stored stencil value while  sten-ciling stenciling
       ciling  is  enabled.   If  the  stencil  test  fails, no change is made to the pixel's color or depth
       buffers, and fail specifies what happens to the stencil buffer contents.  The following  six  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_DECR         Decrements the current stencil buffer value.  Clamps to 0.

       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 subse-quent subsequent
       quent depth buffer tests succeed (zpass) or fail (zfail) (see
       glDepthFunc).  The actions are specified using the same six symbolic constants as  fail.   Note  that
       zfail  is  ignored  when there is no depth buffer, or when the depth buffer is not enabled.  In these
       cases, fail and zpass 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.

ERRORS
       GL_INVALID_ENUM  is  generated  if fail, zfail, or zpass is any value other than the six defined con-stant constant
       stant values.

       GL_INVALID_OPERATION is generated if glStencilOp is executed between the execution of glBegin and the
       corresponding execution of glEnd.

ASSOCIATED GETS
       glGet with argument GL_STENCIL_FAIL
       glGet with argument GL_STENCIL_PASS_DEPTH_PASS
       glGet with argument GL_STENCIL_PASS_DEPTH_FAIL
       glGet with argument GL_STENCIL_BITS
       glIsEnabled with argument GL_STENCIL_TEST

SEE ALSO
       glAlphaFunc(3G), glBlendFunc(3G), glDepthFunc(3G), glEnable(3G), glLogicOp(3G), glStencilFunc(3G)




                                                                                             GLSTENCILOP(3G)