Martin Beckett wrote:
Jason Daly wrote:
If you're familiar with OpenGL, osg::DrawArrays is equivalent to
glDrawArrays(), osg::DrawElements is equivalent to glDrawElements().
The first uses the vertex arrays directly, the second uses an index
array to select vertices from the vertex arrays.
Thank you.
I had it in my mind that glDrawElements() was very slow compared to ranges, and
it was recommended that a large geode was broken down into a number of
osg::DrawArrays
DrawElements is fine. What you don't want to do is use indexed vertex
attributes (for example, osg::Geometry::setVertexIndices() ). That will
force OSG to use glBegin/glEnd, which is never a good idea these days.
The advice about breaking up large geodes is still applicable. If
you're talking about hundreds of thousands of vertices, it's probably
best to represent those as multiple geodes (and group them spatially, if
possible).
What about using 'out of order' osg::DrawElements to group points by location rather than in the vertex order, for easy point picking - is that a good idea?
I don't think that will matter too much as far as performance is
concerned, so it's probably a good idea if it makes your app more usable.
Yes (but still better than using glBegin/glEnd ;-)
Indeed :-)
I will just be editing the points interactively so compared to the speed of the
intersector this shouldn't be a problem.
I'd still disable them. If you're using VBOs and DrawElements
effectively, they probably won't help that much, and you'll have to
recompile the display list each time you make a change, which might
cause frame rate hiccups.
--"J"
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