Collision detection with custom nodes?

[JimC]

When I add:

viz.MainView.collision(viz.ON)

to the end of testCustomNode.py (example script from the plugin API), I can still drive the viewpoint right through the middle of the polygon. What am I missing?

Thanks,
-Jim

[farshizzo]

Is your custom node using raw OpenGL command to render? If so, then collisions won't work because OpenSceneGraph will not know anything about the mesh of your object. There are two ways to handle this:

1) Use the built-in osg::Geometry class to render your object

2) Implement the following osg::Drawable methods in your custom drawable class:

virtual bool supports(osg::PrimitiveFunctor&) const;
virtual void accept(osg::PrimitiveFunctor& pf) const;

These methods allow you to pass information about your mesh to OpenSceneGraph, which will allow it to participate in collision/intersection/pick tests. Here is a very simple example showing how to implement this for a simple quad:

virtual bool supports(osg::PrimitiveFunctor&) const { return true; }

virtual void accept(osg::PrimitiveFunctor& pf) const
{
    pf.begin(GL_QUADS);
    pf.vertex(-1,1,0);
    pf.vertex(1,1,0);
    pf.vertex(1,-1,0);
    pf.vertex(-1,-1,0);
    pf.end()
}

[JimC]

This is just the custom-node example plugin that comes with the plugin API. It draw a single (deforming) square.

I assumed that the Drawable's computeBound() method, which returns a BoundingBox, was used for collision detection. The overridden computeBound() method in the example plugin appears to be returning reasonable values, and it does get called by winviz. If not for collision detection, what is this method for?

-Jim

[JimC]

> If not for collision detection, what is this method for?

Culling?

-Jim

[farshizzo]

The bounding box of the drawable is used for culling.