Hello all, I am working on few NURBS classes and would like to know design guidelines to make them work effectively with rest of OSG. As a start one simple renderer class (based on GLU) and two tesselator classes are on the plate. After reviewing many comments in various articles and forums, it seems converting the surfaces to polygons and rendering them is more practical than trying to evaluate them directly. One tesselator class to divide the surface into uniform triangles and another class to sub-divide based on "curvature" - both are producing a list of triangles from a NURBS surface.
Now I am looking for how to supply this triangle geometry to OSG effectively. I saw the shape classes (such as sphere) and thought I could make NURBS as one more shape derived class, but the shapedrawable class is closed (in the sense it is using ComputeBoundShapeVisitor that is "fixed" for few known types) and not sure if we can extend it (without modifying it). Also the comments in the code say that shape is not a peformance oriented class. So how do we host these triangles that we generate from the surface? If we use DrawElements classes to host these list of triangle, will OSG be able to cull them ? Because all that we will be supplying to DrawElements is a big vector of points and I am not sure if OSG will be able to figure out the bounds that can be culled effectively from that linear vector. (I am of the impression that to for an effective elimination of nodes there should be some kind of parent-child relationship and not just a linear triangle list. Is that correct?) Or is there a better class that we need to derive from implement its methods? Would it do good to group a every 100 or 200 triangles into a geode so that OSG can traverse quickly to eliminate any geodes that fall out of view. Also I read in old posts here that shader support is good for surfaces. If we supply the triangles to the OSG that would automatically make them as shader compatible (since they will be having vertices that can be processed) - or do we need to add any extra explicit support? Looking for any guidelines on how to progress. Thank you for your time and effort. _______________________________________________ osg-users mailing list [email protected] http://lists.openscenegraph.org/listinfo.cgi/osg-users-openscenegraph.org
