Paul Martz wrote on Thursday, April 23, 2009 9:59 AM: > Hi all -- I'd like to see how members of the community are handling this > fairly common OSG problem. > > Imagine that your app needs to modify the scene graph based on the viewpoint > location, view frustum, distance to the viewpoint, etc. This information is > not guaranteed to be available, accurate, or up-to-date until the _end_ of > the update phase, right? Typically this info is only available from the > CullVisitor. But it's too late to modify the scene graph during cull -- it's > not thread safe. So, how does your app handle this situation? > > OSG itself needs to handle this situation in a few places. AutoTransform, > Billboard, LOD, and screen-oriented text, just to name a few. I believe OSG > handles this with a 1-frame latency with these classes (obtains the values > during cull but updates the scene graph during update of the next frame), but > haven't looked at the code in a long time. > > Another way to do this would be to query the viewpoint location / view > frustum during update and modify the scene graph based on those values, even > though those values could still change before the start of cull-draw.
> > But I'm interested in hearing other ideas on how to handle this issue. Thanks > in advance for any feedback. I used a custom cull visitor (which I needed for other reasons, too) to capture the viewpoint data and do the necessary scenegraph modifications. At the time, I also needed more than the float precision given by getEyepoint(), and I was trying to minimize the effects on code that used my library; otherwise, I think I would have gone with a modified update visitor that tracked the current eyepoint(s). -- Bryan Thrall FlightSafety International bryan.thr...@flightsafety.com _______________________________________________ osg-users mailing list osg-users@lists.openscenegraph.org http://lists.openscenegraph.org/listinfo.cgi/osg-users-openscenegraph.org
