Graphics Reference
In-Depth Information
Table 11-2
Stencil Operations
(continued)
Description
Stencil Function
(incrementing the maximum value will result
in a new stencil value of zero) or underflows
(decrementing zero will result in the maximum
stencil value)
GL_KEEP
Keep the current stencil value, effectively not
modifying the value for that pixel
GL_INVERT
Bit-wise invert the value in the stencil buffer
void
glStencilOp
(GLenum
sfail
, GLenum
zfail
,
GLenum
zpass
)
void
glStencilOpSeparate
(GLenum
face
, GLenum
sfail
,
GLenum
zfail
, GLenum
zpass
)
face
specifies the face associated with the provided stencil function.
Valid values are
GL_FRONT
,
GL_BACK
, and
GL_FRONT_AND_BACK
(
glStencilOpSeparate
only).
sfail
specifies the operation applied to the stencil bits if the fragment
fails the stencil test. Valid values are
GL_KEEP
,
GL_ZERO
,
GL_REPLACE
,
GL_INCR
,
GL_DECR
,
GL_INCR_WRAP
,
GL_DECR_WRAP
, and
GL_INVERT
.
zfail
specifies the operation applied when the fragment passes the
stencil test, but fails the depth test
zpass
specifies the operation applied when the fragment passes both
the stencil and depth tests
The following example illustrates using
glStencilFunc
and
glStencilOp
to control rendering in various parts of the viewport:
GLfloat vVertices[] =
{
−0.75f, 0.25f, 0.50f, // Quad #0
−0.25f, 0.25f, 0.50f,
−0.25f, 0.75f, 0.50f,
−0.75f, 0.75f, 0.50f,
(continues)
