bob kuehne - [EMAIL PROTECTED] - 734-834-2696
On Oct 22, 2007, at 6:47 PM, "Paul Martz" <[EMAIL PROTECTED]> wrote: > Thanks for the note, Robert -- > >> The high level approach does suffer from a round trip to the >> graphics card - you still have to wait till all the queries >> are returned before you can dispatch the last bit of data >> into the OpenGL fifo. Claiming this eliminates the latency >> is rather stretching things, it hides it a bit, bit only a >> bit, you are still stalling the CPU till the GPU is done so >> parallelism between the CPU and the GPU is heavily compromised. > > The total time for the hardware to generate the results is the same in > either case, you're right. The "latency" I was referring to is a > visual > latency, not a time latency per se: seeing (or not seeing) the actual > geometry in frame N is based on query results from frame N-1. > > My current implementation suffers from this latency. I'm not pleased > with > the results, and recent discussions (such as the thread concerning > only > rendering when needed rather than with a continuous rendering loop) > indicate > that there are OSG use cases under which such an implementation > would be a > poor choice. > >> Personally I'd rather taking the hit and doing everything in >> one frame rather than having a frame overlap and then having >> to come up with clever frame coherency tricks to ensure that >> you don't get false negatives in the next frame. There are >> certain models types that are already breaking frame by a >> long way - i.e. hitting 10fps, so for these a round trip to >> the GPU is relatively low compared to the potential gain of >> culling geometry and state from the draw dispatch, for these >> occlusion culling in frame will be a godsend. > > Yep, I'm leaning this way as well. So, then, the question becomes: > How to > implement this in OSG? > >> As for mods the rendering backend, I'd suggest some sort >> RenderLeaf extension that allows leaves to be switched off, >> and during draw traversal the switched off leaves are >> ignored. The toggling code be done be the pre RenderStage >> you set up to do the occlusion query. > > Hm. I really want all the occlusion queries to be done after all other > "normal" rendering has finished (to maximize the chance for > occlusion to > occur). So it seems I really want a POST RenderStage that issues the > queries, then iterates looking for available results; as each result > becomes > available, it checks for visibility and renders or skips the actual > Drawables accordingly. > > Also, I don't want to limit this to Drawable-level queries. It is very > useful to be able to perform a single occlusion query to test for the > visibility of an entire subtree. Thoughts on that? > > I'll look into this, but look forward to any additional thoughts or > directions from you. > > Paul Martz > Skew Matrix Software LLC > http://www.skew-matrix.com > 303 859 9466 > > _______________________________________________ > osg-users mailing list > [email protected] > http://lists.openscenegraph.org/listinfo.cgi/osg-users-openscenegraph.org _______________________________________________ osg-users mailing list [email protected] http://lists.openscenegraph.org/listinfo.cgi/osg-users-openscenegraph.org
