Warp wrote:
> John VanSickle <evi### [at] hotmailcom> wrote:
>> Pixar's docs indicate that shooting one reflected ray and/or one 
>> refracted ray for each intersection that has reflection and/or 
>> refraction in the shader, and one shadow ray for each intersection for 
>> each light source, is enough; anti-aliasing is accomplished by jittering 
>> the light sources and the reflected and refracted rays, and setting the 
>> overall anti-aliasing level high enough to reduce granularity to an 
>> acceptable level.
> 
>   In order to get a grain-free smooth result, you would have to shoot
> something like 50 rays per pixel or more (depending on the scene and the
> amount of blurriness). Think about how long it takes for a scene to render
> with that much antialiasing.

The Pixar doc I'm referencing says that they usually need to sample from 
16 to 64 times for each pixel.

The doc is here:

   http://graphics.pixar.com/library/DistributedRayTracing/paper.pdf

Additionally, their method also includes adjusting the rays shot for 
motion blur and focal blur, and it turns out that the overall AA level 
needed is simply the maximum required by any of the effects in play, so 
that the total cost is no greater than that of the most expensive effect.

>   Just sending all the reflected rays at once, however, can be much faster
> in simple cases because it's done only for the reflecting surface. For example,
> this image took just a few minutes to render:
> 
>   http://warp.povusers.org/pics/Rubiks_Revenge2.jpg

Perhaps this can also be handled (and really, should be handled) by 
allowing the user to specify higher AA levels for certain areas of the 
screen that are believed to require it.  If one object has a great deal 
of fine detail, the user should be able to specify a high AA level for 
the pixels that cover it, without forcing the whole frame to be sampled 
at that high level.

It should be simple enough for a user (let's say in POV-Ray) to specify

aa_box {
   <-1,4,2>,<0,5,3>
   aa_level 5
}

and the renderer, prior to rendering scene objects, would mark the frame 
buffer so that the pixels covered by this box get sampled at an AA level 
of five instead of for the overall scene level.  If two such boxes with 
differing AA levels overlap, the overlap area is sampled at the higher 
of the two rates.

Regards,
John

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