[osg-users] "LOS" materail query

[Sebastian Messerschmidt]

Hi Mike
> Hi,
>
> I am wanting to do a dust cloud when an entity (helicopter) lands on a terrain. Ideally, would like the color of the dust cloud to be similar to the material/texture that the entity is on. Is there a way to do a "material/texture color" query based on an entity position, kind of like an LOS intersector test?
> Thank you!

You can use the osgUtil::LineSegmentIntersector to retrieve intersections.
The result will contain the information on the primitives hit, so you 
can get the stateset containing the material properties from there. As 
for the textures: you can also retrieve the texel you hit.
I've attached some code-snippet out of some test-application of mine.

<snip>

if (!mExternalPickPositionHandler.empty() && computeIntersections(view, 
ea, intersections) )
     {
         osg::Vec3d pos = (intersections.begin())->getWorldIntersectPoint();
         osg::Vec3d normal = 
(intersections.begin())->getWorldIntersectNormal();
#ifdef TEST_TEXELS
     // use the nearest intersection
         const osgUtil::LineSegmentIntersector::Intersection& 
intersection = *(intersections.begin());
         osg::Drawable* drawable = intersection.drawable.get();
         osg::Geometry* geometry = drawable ? drawable->asGeometry() : 0;
         osg::Vec3Array* vertices = geometry ? 
dynamic_cast<osg::Vec3Array*>(geometry->getVertexArray()) : 0;
         if (vertices)
         {
             // get the vertex indices.
             const 
osgUtil::LineSegmentIntersector::Intersection::IndexList& indices = 
intersection.indexList;
             const 
osgUtil::LineSegmentIntersector::Intersection::RatioList& ratios = 
intersection.ratioList;

             if (indices.size()==3 && ratios.size()==3)
             {
                 unsigned int i1 = indices[0];
                 unsigned int i2 = indices[1];
                 unsigned int i3 = indices[2];

                 float r1 = ratios[0];
                 float r2 = ratios[1];
                 float r3 = ratios[2];

                 osg::Array* texcoords = 
(geometry->getNumTexCoordArrays()>0) ? geometry->getTexCoordArray(0) : 0;
                 osg::Vec2Array* texcoords_Vec2Array = 
dynamic_cast<osg::Vec2Array*>(texcoords);
                 if (texcoords_Vec2Array)
                 {
                     osg::Vec2 tc1 = (*texcoords_Vec2Array)[i1];
                     osg::Vec2 tc2 = (*texcoords_Vec2Array)[i2];
                     osg::Vec2 tc3 = (*texcoords_Vec2Array)[i3];
                     osg::Vec2 tc = tc1*r1 + tc2*r2 + tc3*r3;
                     //normalize, since negative tex-coords are not 
handled by osg::Image::set/getImage
                     float int_part;
                     if (tc[0] < 0) { tc[0] = 1.0 - modf(tc[0], 
&int_part); }
                     if (tc[1] < 0) { tc[1] = 1.0 - modf(tc[1], 
&int_part); }

                     osg::Texture* texture = 
intersection.getTextureLookUp(osg::Vec3(tc,0));
                     osg::Image* image = nullptr;

                     if (texture && (image = texture->getImage(0)))
                     {
                         osg::Vec4 color = image->getColor(osg::Vec3(tc,0));
                         std::cout << SCRed() << "HIT texture: " << 
image->getFileName() << " at " << color << std::endl;
                         image->setColor(osg::Vec4(color) * 
0.9,osg::Vec3(tc,0));
                         image->dirty();
texture->setDataVariance(osg::Object::DYNAMIC);
                     }
                 }
             }
         }
</snip>
>
> Cheers,
> Mike
>
> ------------------
> Read this topic online here:
> http://forum.openscenegraph.org/viewtopic.php?p=64857#64857
>
>
>
>
>
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