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glStencilFunc - set function and reference value for stencil testing
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.
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.
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
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
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
The following values are accepted by func:
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 ).
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
GL_INVALID_ENUM is generated if func is not one of the eight accepted
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),
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