EXT_stencil_wrap
GL_EXT_stencil_wrap
Date: 4/4/2002 Version 1.2
176
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Various algorithms use the stencil buffer to "count" the number of
surfaces that a ray passes through. As the ray passes into an object,
the stencil buffer is incremented. As the ray passes out of an object,
the stencil buffer is decremented.
GL requires that the stencil increment operation clamps to its maximum
value. For algorithms that depend on the difference between the sum
of the increments and the sum of the decrements, clamping causes an
erroneous result.
This extension provides an enable for both maximum and minimum wrapping
of stencil values. Instead, the stencil value wraps in both directions.
Two additional stencil operations are specified. These new operations
are similiar to the existing INCR and DECR operations, but they wrap
their result instead of saturating it. This functionality matches
the new stencil operations introduced by DirectX 6.
   New Procedures and Functions |
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Accepted by the <sfail>, <dpfail>, and <dppass> parameter of
StencilOp:
INCR_WRAP_EXT 0x8507
DECR_WRAP_EXT 0x8508
| Additions to Chapter 2 of the GL Specification (OpenGL Operation) |
None
| Additions to Chapter 3 of the GL Specification (Rasterization) |
None
| Additions to Chapter 4 of the GL Specification (Per-Fragment Operations and the Framebuffer) |
Section 4.1.4 "Stencil Test" (page 144), change the 3rd paragraph to read:
"... The symbolic constants are KEEP, ZERO, REPLACE, INCR, DECR,
INVERT, INCR_WRAP_EXT, and DECR_WRAP_EXT. The correspond to
keeping the current value, setting it to zero, replacing it with
the reference value, incrementing it with saturation, decrementing
it with saturation, bitwise inverting it, incrementing it without
saturation, and decrementing it without saturation. For purposes of
incrementing and decrementing, the stencil bits are considered as an
unsigned integer. Incrementing or decrementing with saturation will
clamp values at 0 and the maximum representable value. Incrementing
or decrementing without saturation will wrap such that incrementing
the maximum representable value results in 0 and decrementing 0
results in the maximum representable value. ..."
| Additions to Chapter 5 of the GL Specification (Special Functions) |
None
| Additions to Chapter 6 of the GL Specification (State and State Requests) |
None
| Additions to the GLX Specification |
None
None
INVALID_ENUM is generated by StencilOp if any of its parameters
are not KEEP, ZERO, REPLACE, INCR, DECR, INVERT, INCR_WRAP_EXT,
or DECR_WRAP_EXT.
(table 6.15, page 205)
Get Value Type Get Command Initial Value Sec Attribute
------------------------ ---- ------------ ------------- ----- ---------
STENCIL_FAIL Z8 GetIntegerv KEEP 4.1.4 stencil-buffer
STENCIL_PASS_DEPTH_FAIL Z8 GetIntegerv KEEP 4.1.4 stencil-buffer
STENCIL_PASS_DEPTH_PASS Z8 GetIntegerv KEEP 4.1.4 stencil-buffer
NOTE: the only change is that Z6 type changes to Z8
| New Implementation Dependent State |
None
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 |  | Last update: November 14, 2006.
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