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glStencilFunc(3G)
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glStencilFunc - set function and reference value for stencil
testing
void glStencilFunc(
GLenum func,
GLint ref,
GLuint mask );
Specifies the test function. Eight tokens 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. 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. 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.
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().
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: Always fails.
Passes if ( ref & mask ) < ( stencil & mask ). Passes if
( ref & mask ) <= ( stencil & mask ). Passes if ( ref &
mask ) > ( stencil & mask ). Passes if ( ref & mask ) >=
( stencil & mask ). Passes if ( ref & mask ) = ( stencil
& mask ). Passes if ( ref & mask ) <> ( stencil & mask ).
Always passes.
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.
GL_INVALID_ENUM is generated if func is not one of the
eight accepted values.
GL_INVALID_OPERATION is generated if glStencilFunc() is
executed between the execution of glBegin() and the corresponding
execution of glEnd().
glGet() with argument GL_STENCIL_FUNC
glGet() with argument GL_STENCIL_VALUE_MASK
glGet() with argument GL_STENCIL_REF
glGet() with argument GL_STENCIL_BITS
glIsEnabled() with argument GL_STENCIL_TEST
glAlphaFunc(3), glBlendFunc(3), glDepthFunc(3), glEnable(3), glIsEnabled(3), glLogicOp(3), glStencilOp(3),
glStencilFunc(3G)
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