Re: [Openvrml-develop] Simple object to object collision detection in OpenVrml

[Christopher K. S. J. <cs...@qu...>]

Patrick AS Sinclair wrote:
> 
> What's the best way to do this?
> 

 Normally picking is done as a separate traversal, so
you'd need to copy the code that walks the geometry
tree, transforming the point as you go. 

 There isn't code to do that right now, since picking
is done 2d using OpenGL's native picking support.

 For an overview of how it might work, were it to be
implemented, check out the Performer or Inventor
documentation at the SGI site.

 I'd kinda like to see something along theses lines,
but nothing is set in stone:

 1) add code to the core-side so the geometry primitves
spit out triangles (meshes? strips? whatever) instead
of calling over to the opengl side. keeping the geometry
over in core side means a simpler, easier to optimize
opengl layer, it also means...

 2) using (1), you can add generic code to do view frustum
culling, since currently the culling code would need to
reproduce much of the code over in the opengl layer, for
example in order to do extrusions. (right now, extrusions
just aren't culled, which means they render slower sometimes
but doesn't cause any other harm)

 3) using (1), we can then add generic code to do ray-based
(or point-based) picking. right now, to do picking against
extrustions, you'd have to reproduce all the extrustion
rendering code yet again. unlike culling, picking has to
work for everything the first time, you can't just do the
easy bits and leave the rest for later.

 4) using (1,3), add terrain following and avatar collision
code.

 Note that 3d-point-based picking is fairly easy, but true
object-object collision detection doesn't fit very well into
the above framework, it's really a totally separate thing,
you'd probably need to glom on something like vcollide (there
are some articles about this is the various VRML conference
proceedings, if anybody is interested)

 Sorry it took so long, my life has been very, hmmm,
"interesting" lately :-)




-cks













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