Hi Robert et. al.,
> A custom "cull visitor" wouldn't be related to the osgViewer, rather
> it's something you'd instantiate and call yourself on demand. The
> custom "cull visitor" needn't even subclass from CullVisitor. The
> subclass from IntersectionVisitor with a Polytope representing the
> view frustum way actually be the best place to start.
I setup a osgUtil::PolytopeIntersector with a custom
osgUtil::IntersectionVisitor::ReadCallback for loading as you suggested,
but I have two new independent problems with this approach:
1) If I set the PolytopeIntersector to represent the view frustum (as
below), then the IntersectionVisitor will try to load an insane amount
of tiles (i.e. does not work. For the purpose of testing the method of
loading PagedLOD this way I have just set the polytope to a fraction of
the view). I think(?) the problem here is that I don't need the highest
level of detail available - I need the correct level of detail for the
specified camera.
viewport = getCamera()->getViewport();
intersector = new osgUtil::PolytopeIntersector(
osgUtil::Intersector::WINDOW, viewport->x(), viewport->y(),
viewport->width(), viewport->height() );
osgUtil::IntersectionVisitor iv(intersector,_readCallback.get());
getCamera()->accept(iv);
2) The DatabasePager does not pick up on the fact that some PagedLODs
have already been explicitly loaded with: osgDB::readNodeFile(filename,
new osgDB::ReaderWriter::Options("CACHE_ALL")) in my implementation of
osgUtil::IntersectionVisitor::ReadCallback.
I found the earlier thread between Robert and Wojtek titled "Passing
explicitly loaded model to DatabasePager for expiry management"
http://groups.google.com/group/osg-users/browse_thread/thread/b4f1a0abf7f72353/fcd3955ed3e0384e?lnk=gst&q=DatabasePager+IntersectionVisitor#fcd3955ed3e0384e
However, I didn't get the "double caching" trick to work (Wojtek, do you
have any code sample to share?). I even tried to derive DatabasePager
and add code (i.e.: ugly hacks) for making the DatabasePager aware of
explicitly loaded tiles, but with no luck:(
Furthermore, even if I succeed in making the DatabasePager aware of
already loaded tiles, I'm not sure that the intersector approach to
loading the "correct" level of detail will fare any better than the
CustomRenderer approach presented in an earlier posting. Profiling
(callgrind) of both the osgautocapture and the osgintersection example
with "LineOfSight" enabled shows that it is
osgTerrain::GeometryTechnique::generateGeometry() that takes 60-78% for
CPU time (rendering is disabled in both cases).
So the challenge seems to be:
1) Load necessary tiles down to appropriate level of detail _without_
generating geometry.
2) Discard tiles that are that are not needed for specific camera
setting (excluding tiles that already have geometry)
3) Generate geometry for remaining tiles.
4) Render scene, capture image, and exit.
Thanks in advance for any suggestions, idea or relevant code samples:)
Apologies for the lengthy post.
Best regards,
John
Robert Osfield wrote:
Hi John,
A custom "cull visitor" wouldn't be related to the osgViewer, rather
it's something you'd instantiate and call yourself on demand. The
custom "cull visitor" needn't even subclass from CullVisitor. The
subclass from IntersectionVisitor with a Polytope representing the
view frustum way actually be the best place to start.
Robert.
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