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
	      GL_1PASS_SGIS, GL_2PASS_0_SGIS, GL_2PASS_1_SGIS,
	      GL_4PASS_0_SGIS, GL_4PASS_1_SGIS,	GL_4PASS_2_SGIS, and
	      GL_4PASS_3_SGIS.

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 GL_1PASS_SGIS is designed to
     produce a well antialiased	result in a single rendering pass.  Patterns
     GL_2PASS_0_SGIS and GL_2PASS_1_SGIS together specify twice	the number of
     sample points per pixel.  It is intended that a scene be completely
     rendered using pattern GL_2PASS_0_SGIS, then completely rendered again
     using GL_2PASS_1_SGIS.  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)



     GL_4PASS_0_SGIS, GL_4PASS_1_SGIS, GL_4PASS_2_SGIS,	and GL_4PASS_3_SGIS
     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	SGIS_multisample extension, not	part
     of	the core GL command set.  If GL_SGIS_multisample is included in	the
     string returned by	glGetString, when called with argument GL_EXTENSIONS,
     extension SGIS_multisample	is supported by	the connection.


ERRORS
     GL_INVALID_OPERATION is generated if glSamplePatternSGIS is executed
     between the execution of glBegin and the corresponding execution of
     glEnd.


ASSOCIATED GETS
     glGet with	argument GL_SAMPLE_PATTERN_SGI.



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 GL_MULTISAMPLE_SGIS.


















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