Hi Steven, Thanks for the overview, it kinda makes a but more sense.
As general notes, if you can avoid glReadPixels and glDrawPixels calls as these are both very slow, if you can avoid glReadPixels in your alogirithm - try to use an algorithm that doesn't require this. In you explanation it's not clear why you are doing a glReadPixels, and what is in the frame buffer before you do the glReadPixels, so I can't really comment on whether this is doable. Secondly a glDrawPixels is really expensive, you are better off using an osg::Texture2D/TextureRectangle with an osg::Image/osg::PixelBufferObject combination for maximizing copy rate from CPU to GPU. I can't reconcile the word "simulation" with using ray tracing, I presume this isn't a simulator you are developing, and not expect a solid 60Hz. Robert. On Mon, Jun 16, 2008 at 12:42 PM, Watkins, Steven M CIV NSWCDD, G24 <[EMAIL PROTECTED]> wrote: > Hi Robert > > I am probably much more confused than you are at this point! I am working on > a simulation where it was required to incorporate BRLCAD models. BRLCAD are > CSG models, though there are some tools to convert these models to > polygonized formats (ie. STL), these tools generally produce errors on the > more complex geometries. So by including these models into OpenSceneGraph I > am mixing apples with oranges! What I have done so far: > > 1) Incorporated the BRLCAD pre-build libs and dll's in an OpenSceneGraph app. > The BRLCAD is old "C" code that you can not even think about running the .h > files through the C++ compiler. Just use void * pointers and move on. > > 2) Load a BRLCAD model, and generate a "point cloud" to display in > OpenSceneGraph. The points are all determined using the native BRLCAD ray > tracer. The "point cloud" is just to show the model and move around in the > scene with a decent frame rate. Because the next step just kills the frame > rate. > > 3) Once I get the model into the position I want, I toggle into a BRLCAD > ray trace mode, where prior to the swapbuffers: > > - Grab the frame buffer with a glReadPixels call. > - Generate a ray from each pixel location using the SceneView projection > matrix. > - Using the BRLCAD ray tracer determine where/if the ray hit and come up with > a rgb value for the model (simple diffuse lighting model). > - Intersect the OSG scene with the same ray. If there are no intersections > before the BRLCAD intersection, replace the pixel values with BRLCAD derived > rgb values. > - Overwrite the frame buffer with a glDrawPixels. > - Drink lots of coffee, waiting for the scene to render. > > > This works, in that the BRLCAD model is displayed as a "lit" model in the > OpensceneGraph scene. Close up views occasionally show some subpixel? error. > I was looking for a "better" method than above. I do realize that I am out > in the wilderness with this one! > > Thanks > > > > > ________________________________ > > From: [EMAIL PROTECTED] on behalf of Robert Osfield > Sent: Mon 6/16/2008 5:34 AM > To: OpenSceneGraph Users > Subject: Re: [osg-users] Ray Tracing a BRLCAD model in Openscenegraph > > > > Hi Steven, > > I'm confused by what you are actually need to do on the OSG side. You > talk about ray tracing on the OSG side, point clouds, and then talk > about glReadPixels/glDrawPixels, to me they seem un-related so > obviously I'm missing something key to what you are trying to do. > Could you explain for a high level what steps you are taking to create > the scene graph, what operations you need to do on it on the CPU/GPU > and how you need to present/get the results. > > Robert. > > On Tue, Jun 10, 2008 at 12:36 PM, Watkins, Steven M CIV NSWCDD, G24 > <[EMAIL PROTECTED]> wrote: >> Hi All >> >> I have implemented BRLCAD, which is a CSG based ray tracing api, into an >> Openscenegraph application. I am currently displaying BRLCAD models in the >> Openscenegraph world by generating a "point cloud" using the native BRLCAD >> ray tracer and rendering that as Osg point geometry. >> >> I would like to display these BRLCAD models by ray trace in Openscenegraph >> (yes, it will be slow!). I have done some searches through the archives and >> have not found a lot of info. It appears that I am going to have to use >> glReadPixels and glWritePixels prior to the swapbuffers (I am not using >> osgViewer yet). Does anyone know of a better method to render via ray trace >> in Openscenegraph? >> >> Thanks >> >> _______________________________________________ >> 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 > > > > _______________________________________________ > 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
