glSamplePatternSGIS(3G) OpenGL Reference glSamplePatternSGIS(3G)
NAME
glSamplePatternSGIS - set pattern for multisampling
C SPECIFICATION
void glSamplePatternSGIS( GLenum pattern )
PARAMETERS
pattern A symbolic constant that indicates the sampling pattern to be
used when multisampling is enabled. The allowable values are
GL1PASSSGIS, GL2PASS0SGIS, GL2PASS1SGIS,
GL4PASS0SGIS, GL4PASS1SGIS, GL4PASS2SGIS, and
GL4PASS3SGIS.
DESCRIPTION
glSamplePatternSGIS is part of the SGIS_multisample extension. This
extension provides multisampling, a mechanism for antialiasing all GL
primitives: points, lines, polygons, bitmaps, and images. Multisample
antialiasing is most valuable for rendering polygons, because it requires
no sorting for hidden surface elimination, and it correctly handles
adjacent polygons, object silhouettes, and even intersecting polygons.
If only points or lines are being rendered, the "smooth" antialiasing
mechanism provided by the base GL may result in a higher quality image.
This extension is designed to allow multisample and smooth antialiasing
techniques to be alternated during the rendering of a single scene.
The technique is to sample all primitives multiple times at each pixel.
The color sample values are resolved to a single, displayable color each
time a pixel is updated, so the antialiasing appears to be automatic at
the application level. Because each sample includes depth and stencil
information, the depth and stencil functions perform equivalently to the
single-sample mode.
An additional buffer, called the multisample buffer, is required. Pixel
sample values, including color, depth, and stencil values, are stored in
this buffer. When the frame buffer includes a multisample buffer, it
does not also include separate depth or stencil buffers, even if the
multisample buffer does not store depth or stencil values. Color buffers
(left/right, front/ back, and aux) do coexist with the multisample
buffer, however.
The locations of the sample points are relatively static. They change
only when glSamplePatternSGIS is called, and are a repeatable function of
the parameter pattern. The default pattern GL1PASSSGIS is designed to
produce a well antialiased result in a single rendering pass. Patterns
GL2PASS0SGIS and GL2PASS1SGIS together specify twice the number of
sample points per pixel. It is intended that a scene be completely
rendered using pattern GL2PASS0SGIS, then completely rendered again
using GL2PASS1SGIS. When these two images are averaged using the
accumulation buffer, the result is as if a single pass had been rendered
with a pattern of twice the number of sample points. Patterns
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glSamplePatternSGIS(3G) OpenGL Reference glSamplePatternSGIS(3G)
GL4PASS0SGIS, GL4PASS1SGIS, GL4PASS2SGIS, and GL4PASS3SGIS
together define a pattern of four times the number of sample points. They
can be used to accumulate an image after four complete rendering passes.
NOTES
It is not possible to query the actual sample locations of a pixel.
Some sample locations may lie outside the unit square that is considered
to bound the pixel.
glSamplePatternSGIS is part of the SGISmultisample extension, not part
of the core GL command set. If GLSGISmultisample is included in the
string returned by glGetString, when called with argument GLEXTENSIONS,
extension SGISmultisample is supported by the connection.
ERRORS
GLINVALIDOPERATION is generated if glSamplePatternSGIS is executed
between the execution of glBegin and the corresponding execution of
glEnd.
ASSOCIATED GETS
glGet with argument GLSAMPLEPATTERNSGI.
MACHINE DEPENDENCIES
Multisampling is supported only on RealityEngine, RealityEngine2, and VTX
and InfiniteReality systems. Currently it can be used with windows of
multisample-capable Visual types, but not with pixmaps.
SEE ALSO
glSampleMaskSGI, glPushAttrib, glXGetConfig, glXChooseVisual, glEnable
with argument GLMULTISAMPLESGIS.
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