From: ihawkes2++at++csc.com.au
Date: 01/21/2001 16:22:01
Hi,
I am seeing some strange anomalies in my 26 level cliptexture. There are
two distinct effects:
1) Whilst flying over low-res regions of the database (where only 20 levels
are present), small sections of corrupted or misplaced imagery are
sometimes paged into view. Often these sections of imagery are clearly
recognisable as bits of hi-res imagery from other parts of the database.
The sections are paged in/out at a fairly constant distance in front of the
eye point. Turning gridify on (forcing a reload) does not remove corrupted
imagery. In fact, the corrupted bits overlay & obscure the coloured grid.
The attached snapshot snap1 illustrates the problem. A previous email in
1999 "Re: clip texture LOD offset trouble" seems to be describing a similar
problem, and the author has suggested that this is the bug documented in
/usr/share/Performer/doc/clipmap/IRClipmapBugs.txt section 1.1. I have
trouble understanding sections 1.1 and 1.2 of this document - can anyone
give a higher level description of these bugs? Are there any workarounds?
2) The second effect is "striping". Stripes pop up at various places in my
database (both hi-res & low-res areas), often (but not reliably) at
repeatable locations. A stripe consists of a short thin section of
misaligned imagery. Sometimes a stripe appears on its own, other times as a
set of parallel stripes. When a stripe is in view, turning gridify on
(forcing a reload) will remove the stripe. The stripes are aligned with the
cliptexture tex coord axes. The attached snapshots snap2 and snap3
illustrate the problem.
I have been unable to reproduce either problem in clipfly. Examining the
levels in clipgen does not reveal any defects in the data.
To try to fix the problems, I have tried adjusting all the .ct file
parameters (including an invalid border ranging from 8 to 256) to no avail
(see attached .ct file). Note that I use pre-cull callbacks to set my
virtual cliptexture parameters (and yes, I have set
PFN_CULL_SORT_CONTAINED).
My DTR parameters, which I have also experimented with unsuccessfully are currently:
dtrMode = ( MEMLOAD, TEXLOAD );
dtrLoadTime = 1.25; # Milliseconds, per pipe
dtrFadeCount = 5; # Frames
dtrBlurMargin = 0.5;
dtrLoadTimeFrac = 1.0;
I am using Irix 6.5.8f and Performer 2.4 on an Onyx2 IR.
As an aside, does the _PFDRAW_EXERCISE_ARENA environment variable work in 2.4?
Thanks,
Ian Hawkes
CSC Australia
(See attached file: Australia.ct)(See attached file: snap1.jpg)(See attached file: snap2.jpg)(See attached file: snap3.jpg)
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