Wear, Mark (mark.wear++at++lmco.com)
Mon, 04 Jan 1999 08:20:09 -0700
In my application, I use a precull callback to set the virtual LOD offset
for each geode that is drawn. I end up using about 5 different offsets in
any given frame. The approach works well, but I am seeing some texture
artifacts in the scene. At a fairly constant distance from the eyepoint,
texture tiles (maybe only 1?) that appear to be incorrectly placed are
being blended with the surrounding correctly-placed tiles. The result is an
artifact in the distance that disappears as the eyepoint approaches it.
Often, the incorrect tiles are completely black giving the appearance of
rips in the texture. Sometimes however, the tiles are clearly texture from
some other part of the database. This tile that does not belong is rendered
and blended with its neighbors from other levels. This blending helps mask
the problem, but the artifacts are significant enough to render this
approach unusable.
Some of the artifacts appear the be transient, eventually correcting
themselves without eyepoint movement, but this is not always the case. These
incorrectly placed tiles do not appear in an over-head view, only in more
oblique views do they become a problem.
Running the same application using only a single offset for all of the
geodes eliminates the artifacts. Reducing the number of different offsets
(down to 2) does not eliminate the problem. I have tried different blending
techniques without improvement.
I have read section 1.1 (Virtual clipmap alignment granularity vs. number of
good levels) of the IR Virtual Clipmapping Bugs and Limitations document.
I'm not sure if this is what I am seeing, or exactly what this document is
saying.
Here are a few questions. I hope someone has had similar experiences.
Is there some texture mapping calculation that depends upon the LOD offset
that could be using an incorrect offset value because I change it from geode
to geode? (I think the problem would be much worse if this were the case.)
What exactly is section 1.1 (Virtual clipmap alignment granularity vs.
number of good levels) of the IR Virtual Clipmapping Bugs and Limitations
document saying, and if that is my problem what can I do about it?
System:
Onyx II
512 MB
As always, any help would be appreciated.
Mark E. Wear
Electronic Systems Engineer: Real-Time Simulation
Lockheed Martin Vought Systems
(972) 603-2758
mark.wear++at++lmco.com
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