Re: [Raypp-general] Trianlge mesh [was: Suggestion for Load3DS()]

[Martin R. <ma...@MP...>]

Hi Andreas!

>>It's probably better to keep the whole mesh in a single object and build
>>a sort of octtree (or similar) inside it, so that only a small part of the
>>triangles need to be tested.
> 
> 
> I'll check if I could re-use the hmaker for this purpose nethertheless. I
> could
> make the triangle mesh to be one object for the renderer but build my own
> object/triangle hierachy inside the triangle mesh (like you suggest). Is
> this would
> be quite similar to what hmaker does, so the code could be re-used (although
> the interface might have to change a bit for this, maybe make it a template
> class).

I think you should definitely try that. The interface changes shouldn't be
a problem.

> 
> BTW: In the paper I mentioned some time ago (XU Zhi-Yuan, et al: An
> Efficient
> Rejection Test for Ray/Triangle Mesh Intersection) they use a different
> approach.
> They have a fast rejection test for ray/triangle intesection which is based
> on the
> following fact: Given any plane the ray is part of. A triangle then cannot
> intersect
> with the ray, if all its 3 vertices lie on the same side of the a plane. (I
> plan to use
> this rejection test as well).

I'm sure this could help a lot.

> But they do not build a 3D object hierachy like we discuss here. Instead,
> they
> build a quad-tree for the vertices (as seen from the observer), so that the
> position
> of vertices relative to the plane can the determined quickly.
> However, this approach only works for primary rays and only if the primary
> rays
> really come from the same point in space as far as I understood it (which is
> not the
> case if e.g. you do focal blurring).
> Therefore I do not want to use this approach (it would be a nasty to
> implement
> anyway, since the object needs to have information about the observer) but
> go
> the 3D hierachy way.

I agree completely, even if this solution might not be as fast as the one
proposed in the paper. The object shouldn't know about the camera, and should
even work properly for focal blurring and other things we are not even thinking about yet.

Cheers,
   Martin