AO is sounding really really good, especially as a per-object pattern 
function. Dust and shadows would be a realistic use for this, but there are 
other thing that could be done with this to color the serface. It could be 
used to apply grout on tiles, or some strange effect on an alien planet. 
Keep up the good work!

"Gilles Tran" <tra### [at] inapgfr> wrote in message 
news:46961491$1@news.povray.org...

> web.468ea5ce94b248557d55e4a40@news.povray.org...
>
>> Apart from cleverer image-space sampling, damn them, I notice that many
>> other AO implementations allow you to set a maximum search distance 
>> beyond
>> which an AO object will not respond to other objects. Do you use this
>> feature?
>
> Definitely. There are other AO features to consider, basically those that 
> help to control the spread (linear, exponential...) and contrast of the 
> "shadowing". Again, keep in mind that when one uses AO as a (per object) 
> shader, these features are quite mandatory. For instance, AO with a small 
> spread and search distance (and low sampling) will be used on small 
> objects (like a door handle) to give them a patina/dirt effect while AO 
> with a larger spread and search distance will be used for walls to get 
> proper corner shadowing and smooth/hide the radiosity artefacts that tend 
> to crop up in corners.
>
> G.
>

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Well, this was going ok until I ran into meshes (possibly other primitives
as well), which use their own internal bounding hierarchy that the shader
can't access or know about.

The methods I've started using to allow implementation of a user-specified
search distance (and speed up the effect) involve producing a cut-down
bounding hierarchy from the scene for picking up intersections along
occlusion rays, and the mesh's internal bounding sidesteps all of that.

Since I use meshes a lot, I decided not to spend any more time on this for
now. I'm going wait for 3.7 and see what the situation is then. From the
sound of it a lot of the code will have been cleaned up.

Attached is the last attempt, with the occlusion pigment providing the
surface colour (ranging from very dark blue to white), diffuse shading
only. Three lights were used, two of them shadowless. Render time (with
non-exclusive use of the processor) was 55 minutes for 128 occlusion sample
rays and +A0.3 +AM2 +r1, on a 2.4GHz P4. You can get a reasonable preview
quality image in about 7 minutes with between 8-32 sample rays.

Tom

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Attachments:
Download 'ao_54min.jpg' (142 KB)

Preview of image 'ao_54min.jpg'

"Tom York" <alp### [at] zubenelgenubi34spcom> wrote:
> Well, this was going ok until I ran into meshes (possibly other primitives
> as well), which use their own internal bounding hierarchy that the shader
> can't access or know about.
>
> The methods I've started using to allow implementation of a user-specified
> search distance (and speed up the effect) involve producing a cut-down
> bounding hierarchy from the scene for picking up intersections along
> occlusion rays, and the mesh's internal bounding sidesteps all of that.
>
> Since I use meshes a lot, I decided not to spend any more time on this for
> now. I'm going wait for 3.7 and see what the situation is then. From the
> sound of it a lot of the code will have been cleaned up.
>
> Attached is the last attempt, with the occlusion pigment providing the
> surface colour (ranging from very dark blue to white), diffuse shading
> only. Three lights were used, two of them shadowless. Render time (with
> non-exclusive use of the processor) was 55 minutes for 128 occlusion sample
> rays and +A0.3 +AM2 +r1, on a 2.4GHz P4. You can get a reasonable preview
> quality image in about 7 minutes with between 8-32 sample rays.
>
> Tom

Fell on this discussion by accident, I try bumping this up to show interest does
exist: Is this an abandonned project now? or is there an alternative solution in
3.8 through aoi pattern or other "new" features?

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