table of contents
GLSTENCILOP(3G) | [FIXME: manual] | GLSTENCILOP(3G) |
NAME¶
glStencilOp - set front and back stencil test actionsC SPECIFICATION¶
void
glStencilOp(GLenum sfail, GLenum dpfail,
GLenum dppass);
PARAMETERS¶
sfailSpecifies the action to take when the stencil
test fails. Eight symbolic constants are accepted: GL_KEEP,
GL_ZERO, GL_REPLACE, GL_INCR, GL_INCR_WRAP,
GL_DECR, GL_DECR_WRAP, and GL_INVERT. The initial value
is GL_KEEP.
dpfail
Specifies the stencil action when the stencil
test passes, but the depth test fails. dpfail accepts the same symbolic
constants as sfail. The initial value is GL_KEEP.
dppass
Specifies the stencil action when both the
stencil test and the depth test pass, or when the stencil test passes and
either there is no depth buffer or depth testing is not enabled. dppass
accepts the same symbolic constants as sfail. The initial value is
GL_KEEP.
DESCRIPTION¶
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 value in the stencil buffer and a reference value. To enable and disable the test, call glEnable() and glDisable() with argument GL_STENCIL_TEST; to control it, call glStencilFunc() or glStencilFuncSeparate(). There can be two separate sets of sfail, dpfail, and dppass parameters; one affects back-facing polygons, and the other affects front-facing polygons as well as other non-polygon primitives. glStencilOp() sets both front and back stencil state to the same values. Use glStencilOpSeparate() to set front and back stencil state to different values.Keeps the current value.
GL_ZERO
Sets the stencil buffer value to 0.
GL_REPLACE
Sets the stencil buffer value to ref,
as specified by glStencilFunc().
GL_INCR
Increments the current stencil buffer value.
Clamps to the maximum representable unsigned value.
GL_INCR_WRAP
Increments the current stencil buffer value.
Wraps stencil buffer value to zero when incrementing the maximum representable
unsigned value.
GL_DECR
Decrements the current stencil buffer value.
Clamps to 0.
GL_DECR_WRAP
Decrements the current stencil buffer value.
Wraps stencil buffer value to the maximum representable unsigned value when
decrementing a stencil buffer value of zero.
GL_INVERT
Bitwise inverts the current stencil buffer
value.
Stencil buffer values are treated as unsigned integers. When incremented and
decremented, values are clamped to 0 and 2 n - 1, where n is the value
returned by querying GL_STENCIL_BITS.
The other two arguments to glStencilOp specify stencil buffer actions
that depend on whether subsequent depth buffer tests succeed ( dppass)
or fail ( dpfail) (see glDepthFunc()). The actions are specified
using the same eight symbolic constants as sfail. Note that
dpfail is ignored when there is no depth buffer, or when the depth
buffer is not enabled. In these cases, sfail and dppass specify
stencil action when the stencil test fails and passes, respectively.
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 tests always pass, regardless of any call to glStencilOp.ERRORS¶
ASSOCIATED GETS¶
SEE ALSO¶
COPYRIGHT¶
Copyright © 1991-2006 Silicon Graphics, Inc. This document is licensed under the SGI Free Software B License. For details, see http://oss.sgi.com/projects/FreeB/.05/30/2012 | [FIXME: source] |