Hi all, hi Paul,
I have a few questions about OcclusionQueryNode since I'm going to start
using it in our software soon (that's one of the cool things about
having a new stable release of OSG to upgrade to, you get cool new
things to play with! Thanks again for your work on 2.8.3 Paul!)
First of all, running the osgocclusionquery example, I get erratic
results (though this is the one from the svn trunk, not 2.8.3, but my
understanding is that the version in 2.8.3 is basically up to date with
the trunk). For example, if I turn the camera so I see the back of the
box straight-on (perpendicular to the view vector) I get the same stats
as if I view it from the front (i.e. seeing all the lines). If I just
turn the camera slightly so the back is not exactly perpendicular, then
the GPU time goes down considerably (as I'd have expected even when
looking at the back). Is this normal?
The second thing I wonder is that looking at the code, I don't see
anything that lets the OcclusionQueryNode work if the required GL
extensions are not present. I don't see any explicit test for the
required extensions. Perhaps I just missed it, could you point it out to
me if I did? Or is it up to the app to not use OcclusionQueryNodes if
they're not supported on the hardware it's running on?
In particular, in RetrieveQueriesCallback, I see this line of code:
ext->glGetQueryObjectiv( tr->_id, GL_QUERY_RESULT, &(tr->_numPixels) );
glGetQueryObjectiv is defined as this:
void Drawable::Extensions::glGetQueryObjectiv(GLuint id, GLenum pname,
GLint *params) const
{
if (_gl_get_query_objectiv_arb)
_gl_get_query_objectiv_arb(id, pname, params);
else
osg::notify(osg::WARN) << "Error: glGetQueryObjectiv not supported
by OpenGL driver" << std::endl;
}
which means that if it's not supported, then the call will return,
printing a warning, but not modifying tr->_numPixels. But the default
constructor of TestResult sets this to 0. So since there's no test to
see if glGetQueryObjectiv is supported or not before the call, that
means that the geometry under the OQN will always be culled as if it had
0 visible pixels if it's not supported? Surely that's not the intended
result.
Perhaps the TestResult default constructor should set _numPixels to -1,
and then if it stays -1 even after the call to glGetQueryObjectiv, the
OQN should be disabled? Or just explicitly test if glGetQueryObjectiv is
supported...
Any insight into this would be appreciated. I need to make sure my
software runs on any hardware but I'd really like to take advantage of
this "new" feature in OSG... Thanks in advance,
J-S
--
______________________________________________________
Jean-Sebastien Guay jean-sebastien.g...@cm-labs.com
http://www.cm-labs.com/
http://whitestar02.webhop.org/
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