GLSTENCILOP(3G) UNIX Programmer's Manual GLSTENCILOP(3G)
glStencilOp - set stencil test actions
void glStencilOp( GLenum fail,
GLenum zfail,
GLenum zpass )
fail Specifies the action to take when the stencil test
fails. Six symbolic constants are accepted: GL_KEEP,
GL_ZERO, GL_REPLACE, GL_INCR, GL_DECR, and GL_INVERT.
The initial value is GL_KEEP.
zfail Specifies the stencil action when the stencil test
passes, but the depth test fails. zfail accepts the
same symbolic constants as fail. The initial value is
GL_KEEP.
zpass 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. zpass accepts the same
symbolic constants as fail. The initial value is
GL_KEEP.
Stenciling, like depth-buffering, enables and disables draw-
ing 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, out-
lining, 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.
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 fail specifies what happens to
the stencil buffer contents. The following six actions are
possible.
GL_KEEP Keeps the current value.
MirOS BSD #10-current Printed 20.2.2012 1
GLSTENCILOP(3G) UNIX Programmer's Manual GLSTENCILOP(3G)
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_DECR Decrements the current stencil buffer value.
Clamps to 0.
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
2n-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 (zpass) or fail (zfail) (see
glDepthFunc). The actions are specified using the same six
symbolic constants as fail. Note that zfail is ignored when
there is no depth buffer, or when the depth buffer is not
enabled. In these cases, fail and zpass specify stencil
action when the stencil test fails and passes, respectively.
Initially the stencil test is disabled. If there is no sten-
cil buffer, no stencil modification can occur and it is as
if the stencil tests always pass, regardless of any call to
glStencilOp.
GL_INVALID_ENUM is generated if fail, zfail, or zpass is any
value other than the six defined constant values.
GL_INVALID_OPERATION is generated if glStencilOp is executed
between the execution of glBegin and the corresponding exe-
cution of glEnd.
glGet with argument GL_STENCIL_FAIL
glGet with argument GL_STENCIL_PASS_DEPTH_PASS
glGet with argument GL_STENCIL_PASS_DEPTH_FAIL
glGet with argument GL_STENCIL_BITS
glIsEnabled with argument GL_STENCIL_TEST
glAlphaFunc(3G), glBlendFunc(3G), glDepthFunc(3G),
MirOS BSD #10-current Printed 20.2.2012 2
GLSTENCILOP(3G) UNIX Programmer's Manual GLSTENCILOP(3G)
glEnable(3G), glLogicOp(3G), glStencilFunc(3G)
MirOS BSD #10-current Printed 20.2.2012 3
Generated on 2012-02-20 02:47:02 by $MirOS: src/scripts/roff2htm,v 1.70 2011/12/03 18:21:12 tg Exp $
These manual pages and other documentation are copyrighted by their respective writers;
their source is available at our CVSweb,
AnonCVS, and other mirrors. The rest is Copyright © 2002‒2011 The MirOS Project, Germany.
This product includes material
provided by Thorsten Glaser.
This manual page’s HTML representation is supposed to be valid XHTML/1.1; if not, please send a bug report – diffs preferred.