ilbuffer(3G)ilbuffer(3G)NAMEilbuffer - allocates framebuffer space to hold temporary image processing
results
C SPECIFICATION
long ilbuffer(long buffers)
PARAMETERS
buffers the number of 12bit-per-component screen-sized buffers
requested
FUNCTION RETURN VALUE
The returned value of the function is the number of buffers granted.
DESCRIPTIONilbuffer 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.
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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
ildraw, readsource
NOTE
This routine is available only in immediate mode, and only on
RealityEngine running 5.0.1 or later.
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