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John VanSickle <evi### [at] hotmail com> wrote:
> The shadow ray is shot to some random point on the surface of the
> light_source;
[...]
> The reflected ray can be given the strict reflection used in POV-Ray for
> a smooth reflection, or its direction can be jittered to simulate a
> blurred reflection.
> Transparency can be calculated directly from the laws of refraction, or
> the refracted ray can be jittered in order to simulate a translucent
> interior.
> Motion blur is set by selecting a random time within the time slice that
> represents the duration of the frame, and positioning everything
> according to that precise time for that ray shot.
[...]
> Focal blur is done by selecting a focal point and then moving the origin
> of the ray by a random amount for each camera ray.
> With the AA level set to 1x1, the results will be a very grainy image
> where these features are in force, but as the AA level climbs, the grain
> gets averaged out. There are sampling methods that can reduce the
> graininess as well. The paper reports that they seldom need more than
> 64 samples per screen pixel.
While that idea is certainly interesting, I see one big problem with it:
If you have reflective+refractive objects which are very slow to render
(because of all the numerous rays reflecting and refracting and thus
doubling at each intersection point, as is very normal eg. with clear
glass objects), using the AA of 64 samples per pixel will make the
rendering of those objects *very* slow.
The default antialiasing of POV-Ray (method 1 with default settings)
uses at most 9 rays per pixel, which keeps the rendering times of
such objects bearable. I can only imagine how much it will slow down
if instead 64 rays per pixel are shot.
My guess is that Pixar mostly avoids having such objects in their
scenes, and mostly use reflective-only and refractive-only objects,
seldom both at the same time (except if the scene *really* requires it).
--
- Warp
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