Signature
Parameters
| Variables | Description |
|---|---|
| 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
,
where
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
,
where
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
,
where
is the number of bitplanes in the stencil buffer.
The following values are accepted by
func
:
- GL_NEVER
-
Always fails.
- 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
Version Support
| glStencilFunc |
See Also
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/
.
Sample Code References
The following code samples have been found which appear to reference the functions described here. Take care that the code may be old, broken or not even use PyOpenGL.
glStencilFunc
