[osg-users] Questions about vertex and index arrays for geometry

Andreas Goebel a-goebel at gmx.de
Fri Oct 26 02:41:08 PDT 2007


Hello,

I have some questions about how to set up, change dynamically and resize 
vertex and index arrays for geometrys.

So far I have constructed my geometries along the lines of the 
osgGeometry-Example. Whenever the vertices had changed I had assigned a 
new vertex array, and this way everything works.

But: My profiler tells me that I spend much time constructing new 
osg::vec3 and pushing them back to std::vectors all the time.

While I think I could easily just change the vertices within the 
vertex-array the problem is not as simple as that, as not only the 
positions but the number of vertices change.

So my question: Is there a documentation about how to use the 
index-arrays? If not, could please someone explain how to use them?

I would like to
- let the vertex-array stay the same size all the time
- control which vertices are used with an index array

If I have four vertices, is it as easy as pushing back numbers 0, 1, 2, 
1, 2, 3 to the index-array and I get two triangles sharing vertices 1 
and 2? And does the geometry use the index-array automatically if there 
is one? Because at the moment I don´t have an index-array and the 
geometry just uses all the vertices.

And if so, how can I change the size of the index array? Do I have to 
resize the std::vector containing the indices, or is there a way of 
telling osg::geometry about how many indices should be used?

Regards,

Andreas



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