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NAME
glStencilOp - set front and back stencil test actions
C SPECIFICATION
void glStencilOp(GLenum sfail, GLenum dpfail, GLenum dppass);
PARAMETERS
sfail
Specifies 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.
glStencilOp takes three arguments that indicate what happens to the stored stencil value
while stenciling is enabled. If the stencil test fails, no change is made to the pixel's
color or depth buffers, and sfail specifies what happens to the stencil buffer contents.
The following eight actions are possible.
GL_KEEP
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.
glStencilOp() is the same as calling glStencilOpSeparate() with face set to
GL_FRONT_AND_BACK.
ERRORS
GL_INVALID_ENUM is generated if sfail, dpfail, or dppass is any value other than the
defined constant values.
ASSOCIATED GETS
glGet() with argument GL_STENCIL_FAIL, GL_STENCIL_PASS_DEPTH_PASS,
GL_STENCIL_PASS_DEPTH_FAIL, GL_STENCIL_BACK_FAIL, GL_STENCIL_BACK_PASS_DEPTH_PASS,
GL_STENCIL_BACK_PASS_DEPTH_FAIL, or GL_STENCIL_BITS
glIsEnabled() with argument GL_STENCIL_TEST
VERSION SUPPORT
┌────────────┬───────────────────────────────────────────────────────────────────────┐
│ │ OpenGL Version │
├────────────┼─────┬─────┬─────┬─────┬─────┬─────┬─────┬─────┬─────┬─────┬─────┬─────┤
│Function │ 2.0 │ 2.1 │ 3.0 │ 3.1 │ 3.2 │ 3.3 │ 4.0 │ 4.1 │ 4.2 │ 4.3 │ 4.4 │ 4.5 │
│/ │ │ │ │ │ │ │ │ │ │ │ │ │
│Feature │ │ │ │ │ │ │ │ │ │ │ │ │
│Name │ │ │ │ │ │ │ │ │ │ │ │ │
├────────────┼─────┼─────┼─────┼─────┼─────┼─────┼─────┼─────┼─────┼─────┼─────┼─────┤
│glStencilOp │ ✔ │ ✔ │ ✔ │ ✔ │ ✔ │ ✔ │ ✔ │ ✔ │ ✔ │ ✔ │ ✔ │ ✔ │
└────────────┴─────┴─────┴─────┴─────┴─────┴─────┴─────┴─────┴─────┴─────┴─────┴─────┘
SEE ALSO
glBlendFunc(), glDepthFunc(), glEnable(), glLogicOp(), glStencilFunc(),
glStencilFuncSeparate(), glStencilMask(), glStencilMaskSeparate(), glStencilOpSeparate()
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/.
COPYRIGHT
Copyright © 1991-2006 Silicon Graphics, Inc.
Copyright © 2010-2014 Khronos Group
[FIXME: source] 01/03/2018 GLSTENCILOP(3G)