Hi Paul, The OSG has a range of culling approaches, and support for OpenGL fast paths.
W.r.t. back face culling, this is just an OpenGL operation done during triangle set, its not a high level culling operation, and as such only saves of fill rate. The OSG does support cluster culling which is a bit like back face culling, but is a test that can be inserted via the osg::ClusterCullingCallback. into any node in the scene. This is great of whole earth paged database when you can cull the back faces of the earth. I have to say, the OSG has almost all the tools you could use for get best performance, but and this is a big but it does depend upon databases that are well conditioned. Database optimization is a huge huge topic that I won't go into now. Please browse the archives on this topic. Robert. On 6/28/07, Paul Kahler <[EMAIL PROTECTED]> wrote:
I've been poking around on the OSG site and the mailing list and it's not clear to me how well OSG scales with geometric complexity (polygon count). I understand view frustum culling and back-face culling, but it's not clear to me if OSG can do more than that. For example, if I have an entire town modeled with terrain, buildings, furniture, under what conditions will OSG skip drawing a chair inside a room? Or more simply, what does OSG do to skip rendering objects obstructed by other objects? Speaking theoretically: back-face culling eliminates about 1/2 of all polygons. View frustum culling eliminates perhaps all but 1/4 of polygons in a large city viewed from the middle of town. From a time complexity standpoint this turns a O(n) problem where n is the number of polygons, into O(n/8) which is really just k*O(n) = O(n). A constant improvement but still linear. Does OSG do better? How? I understand that creating impostors and using LOD techniques can also improve performance, but my question is strictly in regard to methods that don't simplify geometry (i.e. culling). Thanks, Paul _______________________________________________ osg-users mailing list [email protected] http://openscenegraph.net/mailman/listinfo/osg-users http://www.openscenegraph.org/
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