fglStencilOp man page on IRIX

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fglStencilOp(3G)	       OpenGL Reference		      fglStencilOp(3G)

NAME
     fglStencilOp - set stencil test actions

FORTRAN SPECIFICATION
     SUBROUTINE fglStencilOp( INTEGER*4 fail,
			      INTEGER*4 zfail,
			      INTEGER*4 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 fglEnable and fglDisable with
     argument GL_STENCIL_TEST; to control it, call fglStencilFunc.

     fglStencilOp 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
		     fglStencilFunc.

									Page 1

fglStencilOp(3G)	       OpenGL Reference		      fglStencilOp(3G)

     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
						   n
     and decremented, values are clamped to 0 and 2 -1, where n is the value
     returned by querying GL_STENCIL_BITS.

     The other two arguments to fglStencilOp specify stencil buffer actions
     that depend on whether subsequent depth buffer tests succeed (zpass) or
     fail (zfail) (see
     fglDepthFunc).  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 fglStencilOp.

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 fglStencilOp is executed between the
     execution of fglBegin and the corresponding execution of fglEnd.

ASSOCIATED GETS
     fglGet with argument GL_STENCIL_FAIL
     fglGet with argument GL_STENCIL_PASS_DEPTH_PASS
     fglGet with argument GL_STENCIL_PASS_DEPTH_FAIL
     fglGet with argument GL_STENCIL_BITS
     fglIsEnabled with argument GL_STENCIL_TEST

SEE ALSO
     fglAlphaFunc, fglBlendFunc, fglDepthFunc, fglEnable, fglLogicOp,
     fglStencilFunc

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