Index for Section 3G

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glStencilOp(3G)
NAME
  glStencilOp - set stencil test actions

SYNOPSIS
  void glStencilOp(
	  GLenum fail,
	  GLenum zfail,
	  GLenum zpass );

PARAMETERS
  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.

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().

  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.

  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 2 sup 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 (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.

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
  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 execution of glEnd().

ASSOCIATED GETS
       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

SEE ALSO
  glAlphaFunc(3), glBlendFunc(3), glDepthFunc(3), glEnable(3), glLogicOp(3),
  glStencilFunc(3)

Index for Section 3G

Alphabetical listing for G

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