glStencilFunc(3G)glStencilFunc(3G)NAMEglStencilFunc - 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. 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 sten‐
cil buffer. To enable and disable the test, call glEnable() and glDis‐
able() 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 compari‐
son. 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 suc‐
ceeds is the pixel passed through to the next stage in the rasteriza‐
tion 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 ) <= ( sten‐
cil & 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
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
ASSOCIATED GETSglGet() 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
SEE ALSOglAlphaFunc(3), glBlendFunc(3), glDepthFunc(3), glEnable(3), glIsEn‐
abled(3), glLogicOp(3), glStencilOp(3),