Hi, I am also very surprised to see that use of index arrays/buffer objects impacts performance. Is this a limitation of OSG or OpenGL ? I always thought that Hardware Vertex Buffer + Hardware Index Buffer should be the best performing scenario.
I just checked GPU_Programming_Guide on NVidia Developer site and found following excerpt in Chapter 3 General GPU Performance Tips: " ... 3.3 Vertex Shader 3.3.1 Use Indexed Primitive Calls Using indexed primitive calls allows the GPU to take advantage of its post-transform-and-lighting vertex cache. If it sees a vertex it's already transformed, it doesn't transform it a second time-it simply uses a cached result. ... " It seems to contradict what Robert said... Cheers, Wojtek ----- Original Message ----- From: "Thibault Genessay" <[EMAIL PROTECTED]> To: "OpenSceneGraph Users" <osg-users@lists.openscenegraph.org> Sent: Monday, January 07, 2008 11:28 AM Subject: Re: [osg-users] VBO > Hi all, > > I know this is slightly off-topic, but if some of you have 5 minutes > to waste, please read on :) > I just take the occasion to ask a question regarding Robert's latest > comment: > >> So if you want fast paths absolutely never ever ever used vertex >> indices. Vertex indices are there in the OSG purely for backwards >> compatibility and are not something I'd recommend usage today. > > Acknowledged. Now, what is the preferred way to render triangle > strip-based geometries where all strips are parallel and share an edge > ? Should we duplicate all common vertices ? e.g. I have a 1080 * 31 > patch, rendered as 30 tri strips (basically, it's a 3D plot). I use > indexed rendering so I have 33480 vertices. Now if I want to switch to > "fast-path", does it mean I'm going to need 2*1080*30 = 64800 vertices > ? > Given the amount of info for each vertex (color, texcoords, ...) this > seems a pretty big memory impact to me (and if the T&L has to be > performed again, it can also be a slowdown, can't it ?). I am no > cutting-edge 3D expert so please forgive my ignorance. > > Happy new year to everyone, > > Thibault > _______________________________________________ > osg-users mailing list > osg-users@lists.openscenegraph.org > http://lists.openscenegraph.org/listinfo.cgi/osg-users-openscenegraph.org > _______________________________________________ osg-users mailing list osg-users@lists.openscenegraph.org http://lists.openscenegraph.org/listinfo.cgi/osg-users-openscenegraph.org
