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>> I thought the entire definition of AO is that it's a rough
>> approximation to true GI that's useful because it renders really fast?
>
> Indeed. Raytracers typically cast out a few rays (the more the smoother
> the result) to see if they hit anything within a certain distance. GPU
> methods typically just compare the depths of the surrounding pixels (so
> it's essentially done in 2D). Obviously for a GPU this is much faster
> as it doesn't need to access the scene data (it might not even exist in
> most cases!).
Ah, wait... Apparently I'm confusing SSAO with normal AO. (The former
being commonly run on the GPU, the latter requiring an actual ray
tracer.) I wasn't aware that Blender is doing true AO. I assumed it was
just faking it, GPU-style.
>> (I idea why AA would be better...)
>
> AFAIK standard GPU rendering uses a very limited AA algorithm (usually
> fixed to a certain number of sub-pixels and some maximum like 8x), a
> raytracer usually can use dynamic AA depth and as many rays as are
> necessary.
This puzzles me. I'm not disputing you're wrong - usually there's some
option to set the number of subsamples taken - but since a GPU can
*only* draw straight lines, you'd think they could just use the
closed-form formulas for doing mathematically perfect AA on polygon
edges. It takes about 3 float-ops. No subsamples required.
Weird...
>> I guess I usually think of the main advantage of ray-tracing as being
>> the ability to render things that aren't triangles.
>
> I think there are some raytracers that can *only* render triangles.
Apparently I'm looking at one.
> I
> guess it makes them simpler and they can be highly optimised for huge
> lists of triangles. Then you can make some layer that converts higher
> order shapes to pixel sized triangles on the fly to feed the raytracer
> if needed. IIRC this is how Pixar's raytracer works.
That's what I heard. I also hear that only about 0.1% of the stuff Pixar
does actually involves any ray tracing, with is kind of unbelievable...
I still find it rather hard to believe that you can take a complex shape
such as the surface of a water splash and automatically tesselate it.
But apparently somebody has figured out how to do this.
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