[osg-users] Computing Normals for Drawables

James Buckthorpe James.Buckthorpe at gmail.com
Fri Nov 6 08:18:15 PST 2009


Hi,

I have a scene that contains a very large number of osg::Drawables.

I am currently using osg::SmoothingVisitor to compute the normals for each geometry. This creates a normal per vertex. If I turn normals off I see a sigificant reduction in the amount of memory in use, hence I am currently looking at implementing a visitor to compute 1 normal per triangle which would still give the appearance I need and reduce the memory load.

However, I am not sure of the correct way to binding normals to the geometry:

In osg::SmoothingVisitor this is done using:

geom.setNormalArray( normals );
geom.setNormalIndices( geom.getVertexIndices() );
geom.setNormalBinding(osg::Geometry::BIND_PER_VERTEX);

My geometries are mostly defined using quads and triangle strips. If I use osg::Geometry::BIND_PER_PRIMITVE I am guessing that this will try to bind to a quad or triangle strip not a triangle as I would like. Is this correct?
Using a single normal for a triangle strip is not going to give me a suitable view of the geometry.

Is anyone able to point me in the right direction?

Many Thanks for your help.
James

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