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ilbuffer(3G)							  ilbuffer(3G)

NAME    [Toc]    [Back]

     ilbuffer -	allocates framebuffer space to hold temporary image processing

C SPECIFICATION    [Toc]    [Back]

     long ilbuffer(long	buffers)

PARAMETERS    [Toc]    [Back]

     buffers	the number of 12bit-per-component screen-sized buffers

     The returned value	of the function	is the number of buffers granted.

DESCRIPTION    [Toc]    [Back]

     ilbuffer attempts to allocte buffers 12bit/component color	buffers	that
     span the entire display surface.

     On	the RealityEngine, a 12bit/componenent color buffer consumes 3 16bit
     framebuffer words.	 A count of the	deepest	pixel currently	used is
     maintained	by the Kernel graphics driver. The count is always at least 9
     16bit words, the value required to	support	2 12bit/component color
     buffers and a Z/stencil buffer.  The remainder of the pixel depth can be
     allocated to the caller for use as	temporary image	processing storage.

     Any requests by other graphics contexts to	use pixel depths that would
     extend into the allocated buffer are denied until the buffer is
     explicitly	freed by ilbuffer(0), or the graphics context (window) is
     destroyed.	Equivalently, if a graphics context uses features that require
     all of the	pixel depth, ilbuffer may return 0. The	resource is not
     virtualized and is	allocated first	come, first served.

     For example on a RealityEngine running with small pixel depth, 12 16bit
     framebuffer words available for graphics features.	Six are	required for
     double color buffers and three for	Z/stencil. That	leaves three that
     could be alloced for 1 ilbuffer if	no other program has allocated a pixel
     depth greater than	9 impwords.

     On	a RealityEngine	running	with medium pixel depth, 28 16bit framebuffer
     words are available for graphics features.	Nine are required for basic
     double buffered Zbuffer operation,	so 19 16bit words are available	to be
     allocated as 6 ilbuffers if no other program has allocated	a pixel	depth
     greater than 9 16bit framebuffer words.

     Multiple contexts may allocate the	same framebuffer space through calls
     to	ilbuffer, but the ilbuffer is not virtualized (context switched), so
     user contexts must	synchronize the	use of this buffer themselves. The
     ImageLibrary uses this feature, so	concurrent use of the ImageLibrary
     when it is	using hardware acceleration and	user programs that use this
     feature will not necessarily work together	correctly. One possibility is
     to	cause the ImageLibrary to use only the CPU while user programs use
     this feature.

									Page 1

ilbuffer(3G)							  ilbuffer(3G)

     The ilbuffers can be selected for drawing with ildraw or as a readsource
     for pixel copies or framebuffer to	texture	loads with readsource

SEE ALSO    [Toc]    [Back]

     ildraw, readsource

NOTE    [Toc]    [Back]

     This routine is available only in immediate mode, and only	on
     RealityEngine running 5.0.1 or later.

									PPPPaaaaggggeeee 2222
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