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

VERSION SUPPORT

       ┌──────────────┬───────────────────────────────────────────────────────────────────────┐
       │              │                OpenGL Version                                         │
       ├──────────────┼─────┬─────┬─────┬─────┬─────┬─────┬─────┬─────┬─────┬─────┬─────┬─────┤
       │Function      │ 2.0 │ 2.1 │ 3.0 │ 3.1 │ 3.2 │ 3.3 │ 4.0 │ 4.1 │ 4.2 │ 4.3 │ 4.4 │ 4.5 │
       │/             │     │     │     │     │     │     │     │     │     │     │     │     │
       │Feature       │     │     │     │     │     │     │     │     │     │     │     │     │
       │Name          │     │     │     │     │     │     │     │     │     │     │     │     │
       ├──────────────┼─────┼─────┼─────┼─────┼─────┼─────┼─────┼─────┼─────┼─────┼─────┼─────┤
       │glStencilFunc │  ✔  │  ✔  │  ✔  │  ✔  │  ✔  │  ✔  │  ✔  │  ✔  │  ✔  │  ✔  │  ✔  │  ✔  │
       └──────────────┴─────┴─────┴─────┴─────┴─────┴─────┴─────┴─────┴─────┴─────┴─────┴─────┘

SEE ALSO

       glBlendFunc(), glDepthFunc(), glEnable(), glLogicOp(), glStencilFuncSeparate(),
       glStencilMask(), glStencilMaskSeparate(), glStencilOp(), glStencilOpSeparate()

COPYRIGHT

       Copyright © 1991-2006 Silicon Graphics, Inc. Copyright © 2010-2014 Khronos Group. This
       document is licensed under the SGI Free Software B License. For details, see
       http://oss.sgi.com/projects/FreeB/.

COPYRIGHT

       Copyright © 1991-2006 Silicon Graphics, Inc.
       Copyright © 2010-2014 Khronos Group

[FIXME: source]                             01/03/2018                          GLSTENCILFUNC(3G)