Страницы справочника OS X

Эта страница руководства является частью версии 5.0 Инструментов XCode

Читать страницы руководства

GLSTENCILFUNC(3G)                                OpenGL 3.3                                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 (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/.



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