NAME

       glStencilFuncSeparate - set front and/or back function and reference value for stencil
       testing

C SPECIFICATION

       void glStencilFuncSeparate(GLenum face, GLenum func, GLint ref, GLuint mask);

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.

       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. 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 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, as
       if glStencilFuncSeparate() were called with face set to GL_FRONT_AND_BACK.

       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.

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(), glStencilFunc(), glStencilMask(),
       glStencilMaskSeparate(), glStencilOp(), glStencilOpSeparate()

COPYRIGHT

       Copyright © 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/.

AUTHORS

       opengl.org