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glStencilFunc - set function and reference value for stencil testing
eqn not supported
void glStencilFunc( GLenum func,
GLuint mask )
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
- 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,$2 sup n - 1$], 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.
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,$2 sup n - 1$], 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,$2 sup n - 1$], where $n$ is
the number of bitplanes in the stencil buffer.
The following values are
accepted by func:
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.
- Always fails.
- Passes if ( ref & mask )
< ( stencil & mask ).
- Passes if ( ref & mask ) <= ( stencil & mask
- Passes if ( ref & mask ) > ( stencil & mask ).
if ( ref & mask ) >= ( stencil & mask ).
- Passes if ( ref & mask ) =
( stencil & mask ).
- Passes if ( ref & mask ) != ( stencil & mask
- Always passes.
generated if glStencilFunc is executed between the execution of glBegin
and the corresponding execution of glEnd.
glGet with argument
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
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