[osg-users] osgUtil::IntersectionVisitor, information on polygon intersected

Jean-Sébastien Guay jean-sebastien.guay at cm-labs.com
Wed Sep 17 11:02:06 PDT 2008

Hi Claudio,

> is it possibile with osgUtil::IntersectionVisitor, know what is 
> intersected polygon (example the number 2 or the named "ad32") and which 
> texture is mapped to this polygon?(the name of file which contains the 
> texture)

See the documentation of osgUtil::LineSegmentIntersector::Intersection. 
(which you get from the LineSegmentIntersector which you gave to the 


In the Public Attributes:
* nodePath is the path to the node that was hit for this intersection
* drawable is the drawable that was hit (osg::Geometry or whatever)
* primitiveIndex is the index of the primitive that was hit, so if 
drawable is an osg::Geometry which has one primitiveSet in mode 
GL_TRIANGLES, primitiveIndex would be the triangle index that was hit 
(formed of vertices 3*primitiveIndex, 3*primitiveIndex+1 and 
3*primitiveIndex+2 in the geometry's vertex array). How to get the 
primitive/vertices independently of primitive set mode, I don't know, 
you'll have to work that out yourself. There must be some code in OSG 
that does this already, check the osgpick example or look around in the 
OSG sources.
* To get the texture, just traverse the nodePath and get the last 
texture once you get to drawable (checking the nodes' statesets). You 
can't get the texture filename like that, but perhaps you can have a map 
of filename to texture* in your app and make the correspondence that way.

(the rest is speculation, someone please correct me if I'm wrong)

I think ratioList is the barycentric coordinates of where the hit 
occurred on the polygon (i.e. if it was a triangle that was hit, there 
will be 3 ratios in ratioList, which you can then use to find out where 
in the triangle the hit occurred by multiplying the 3 vertices of the 
triangle by the 3 ratios) but I'm not sure. If that's the case, you can 
do the same with the triangle's texture coordinates at the 3 same 
vertices and thus get where in the texture the hit occured.

In general, you should get acquainted with the doxygen-generated 
reference documentation, and be prepared to navigate through the pages 
in it to find out how to "connect" things together and where to get the 
information you need.

Hope this helps,

Jean-Sebastien Guay    jean-sebastien.guay at cm-labs.com

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