In order to render a large amount of identical primitives, you probably want to use either instancing or geometry shaders. If your target hardware supports OpenGl 3.x features, then the latter is better. You can use arrays of per-vertex data to specify the differences between your spheres (radius, colour etc), create your osg::geometry as a list of points and have your geometry shader expand that into spheres.
For the spheres themselves, it's far quicker to create them as camera-facing impostors, and have your fragment shader just draw spheres for each of them (various examples are available on the web), which can be lit as needs be. The trouble is that they will be flat, which might not be ideal if many of your spheres intersect. You could at least save some triangles by generating camera-facing hemispheres. I'm not sure what the effect would be if you changed the z-values in the fragment shader, but I am advised that's not a good idea, because it means z-buffer-testing can't be done before your fragment shader is run. If you're stuck with older or mobile hardware, then (extensions permitting) you can use shader instancing to do the same thing. Create a single sphere (or hemisphere or quad, for an impostor) , put your per-instance data into a texture, and sample that texture in your vertex shader (ensure you set your texture filtering modes appropriately). There is an example osgdrawinstanced supplied with the OpenSceneGraph distribution that shows you basically how that is done. If you don't have the instancing extension available (MESA software rendering, some older mobile OpenGLES 2 chipsets, VERY old desktop hardware) you need to just make sure you render them in large batches of vertices, which means making 1, or only a few Geometries containing multiple spheres (or quads if you can still use a vertex shader to orient them). Quite a lot of ideas there for things to try, I think, apologies if any of that is a bit confusing. Alistair Baxter Software Engineer ________________________________ Have you downloaded your FREE copy of FieldMove Clino? Find out more about our app for iPhone and Android smartphones: http://news.mve.com/fieldmoveclino Midland Valley Exploration Ltd. 144 West George Street Glasgow G2 2HG United Kingdom Tel: +44 (0) 141 332 2681 Fax: +44 (0) 141 332 6792 The structural geology experts From: [email protected] [mailto:[email protected]] On Behalf Of Trajce Nikolov NICK Sent: 02 December 2013 13:50 To: OpenSceneGraph Users Subject: [osg-users] rendering millions of spheres Hi Community, I remember someone has faced this problem and I think with some solution. Anyone knowing some pointers willing to share some hints, techniques? Thanks a bunch Nick -- trajce nikolov nick
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