>  If the ray hits a triangle in a nearer octree node, there's absolutely
no way that a triangle in a farther octree node would be nearer.

Well, there's that word, "if". If it doesn't hit
the nearer octree node, then another one has to be tested.


>   If you want any speed, you will need to perform a spatial tree
optimization
to your scanline rendering algorithm as well. AFAIK commercial high-end
renderers do this.

Yes, I agree that's a given. Using POV-Ray as
infrastructure is good in this respect
since it has raycasting in which to help build
such trees. Games of course do this (BSP, portals, etc.).
I think the attraction of scanline in film was
that many scenes are in rooms, where setting
up spatial culls is less demanding.


>  You need perspective-correct interpolation (linear interpolation will
give you awful results), which is less trivial.

True, except for micropolygons. My particular prototype
does draw macropolygons, so I will need to do that.
In REYES, it's not necessary.


>   You don't need to load meshes to memory, you only need to know their
> bounding box. When a ray hits the bounding box, you load the mesh. If a
> ray never hits the bounding box of a mesh, that mesh is never loaded.
> Understand?

Yes, I see what you're saying. So you would
load the bboxes of the geometry by themselves,
and then they would fill with the actual
respective geometry as initial hits occurred.
Yes, that's doable. You eventually wind
up with only the necessary geometry.
For some reason I thought you meant trying to
load/unload. Sorry about that.

I guess a developer might reason that, worst case,
you need to have enough memory for all objects,
so why bother adding the (albeit slight) overhead
of doing the first-time hit test. But I can see
this being a win on distributed or shared resource
systems when rendering movies or different view
angles of stills, because statistically more RAM
would be available to other tasks. POV would
definitely benefit, because when it animates
it reparses the .pov file for each frame. So as
you zoom in on a scene, less and less geometry
would get loaded (assuming no reflected rays that
wind up hitting the off-camera objects, at least).

I don't want to get into a scanline vs. raytracing
debate (except to collect the pros and cons of
each approach) because I want to augment POV-Ray, not replace
its raytracer. Hybrid renderers offer a compelling
wealth of strengths. Maybe a person doesn't need
to scanline anything most of the time, but
it's nice to know that he could if he wanted to.
For me, it's about having choice. I don't want
to invest lots of time learning POV and then
be forced to always raytrace when scanlining
might offer a big speed benefit on a particular job
or various parts of a job.

Thanks,
Ray

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