"Hj. Malthaner" <me@home> wrote:

> The BRDFs are still making my head spin. I understand the concept, but
> struggle with the actual math to come up with proper BRDFs for new
> materials of my own.

Diagrams are definitely your friend.
Drawing the diagram with POV-Ray using the math that you're trying to work out
is also an excellent exercise.

I also found this video extremely useful

https://www.youtube.com/watch?v=gsZiJeaMO48

> In regard to the parser, I want to say thanks to the people who wrote
> the PovRay documentation. Each SDL element is documented with a snippet
> of a grammar, which can be converted almost one to one into a recursive
> descend parser. So the documentation is already there. I'll try to keep
> the identifiers used in the parser code close to the ones used the
> documented grammar, so the code will look familiar to those who looked
> at the grammar from the documentation before.

Maybe before you get too far into that, take a look at:
https://journal.stuffwithstuff.com/2011/03/19/pratt-parsers-expression-parsing-made-easy/

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"Hj. Malthaner" <me@home> wrote:
> Something though that I had been missing in PovRay is what is known as
> global illumination or path based lighting. Radiosity, supported by
> PovRay, is very similar, but not quite the same.

Are you aware of the UberPOV fork?

https://github.com/UberPOV/UberPOV

It's based on POV-Ray 3.7 and hasn't really seen any development for some time,
but one of its notable features is stochastic global illumination as an
extension to radiosity. I still use it quite often because I think it produces
much better results than the standard radiosity with almost no tweaking
required.

Maybe there's something there of interest relevant to your project!

Bill

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On 7/18/24 15:38, Bill Pragnell wrote:

> Are you aware of the UberPOV fork?
> 
> https://github.com/UberPOV/UberPOV

Now I am. Well, I had heard of UberPOV before but never really looked 
into it ...

> It's based on POV-Ray 3.7 and hasn't really seen any development for some time,
> but one of its notable features is stochastic global illumination as an
> extension to radiosity. I still use it quite often because I think it produces
> much better results than the standard radiosity with almost no tweaking
> required.

That matches my own impression and why I wanted something with global 
illumination while still supporting PovRay SDL. This is quite 
interesting, thank you for the link!

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On 7/17/24 21:08, Bald Eagle wrote:
> "Hj. Malthaner" <me@home> wrote:
> 
>> In regard to the parser,
> 
> Maybe before you get too far into that, take a look at:
>
https://journal.stuffwithstuff.com/2011/03/19/pratt-parsers-expression-parsing-made-easy/

Interesting, I had not heard of PRATT parsers before.

I think I'll stick with a recursive descent parser though, because it's 
a more widely known approach, even if the code is less compact.

The structure of a recursive descent parser resembles the grammar quite 
closely which a benefit too, I think, with the grammar being of the docs 
already.

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On 7/17/24 21:08, Bald Eagle wrote:

> I also found this video extremely useful
> 
> https://www.youtube.com/watch?v=gsZiJeaMO48

I haven't watched it all yet, but it indeed seems interesting. Thank you 
for sharing the link!

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Op 18-7-2024 om 16:32 schreef Hj. Malthaner:
> On 7/18/24 15:38, Bill Pragnell wrote:
> 
>> Are you aware of the UberPOV fork?
>>
>> https://github.com/UberPOV/UberPOV
> 
> Now I am. Well, I had heard of UberPOV before but never really looked 
> into it ...
> 
>> It's based on POV-Ray 3.7 and hasn't really seen any development for 
>> some time,
>> but one of its notable features is stochastic global illumination as an
>> extension to radiosity. I still use it quite often because I think it 
>> produces
>> much better results than the standard radiosity with almost no tweaking
>> required.
> 
> That matches my own impression and why I wanted something with global 
> illumination while still supporting PovRay SDL. This is quite 
> interesting, thank you for the link!
> 
> 

Even better, 'stochastic' is also supported by version 3.8! I generally use:

+am3 +a0.01 +ac0.90 +r3

and in the radiosity block a count between 10 and 50

varying +a, +ac and +r values increases/decreases the stochastic quality 
(and render time!).

THere must be some documentation by clipka but I am unable to find it 
presently, sorry.


-- 
Thomas

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Thomas de Groot <tho### [at] degrootorg> wrote:
> Even better, 'stochastic' is also supported by version 3.8! I generally use:
>
> +am3 +a0.01 +ac0.90 +r3
>
> and in the radiosity block a count between 10 and 50
>
> varying +a, +ac and +r values increases/decreases the stochastic quality
> (and render time!).

Are we talking about the same thing here?

I was referring to the unbiased purely stochastic version of radiosity, which
was a significant change to the algorithm; I was under the impression that this
wouldn't end up in main POV-Ray in the form it was implemented in UberPOV. Maybe
I missed something, is this in v3.8 now, or are you referring to improvements to
sampling alone?

Bill

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Op 18-7-2024 om 19:49 schreef Bill Pragnell:
> Thomas de Groot <tho### [at] degrootorg> wrote:
>> Even better, 'stochastic' is also supported by version 3.8! I generally use:
>>
>> +am3 +a0.01 +ac0.90 +r3
>>
>> and in the radiosity block a count between 10 and 50
>> 
>> varying +a, +ac and +r values increases/decreases the stochastic quality
>> (and render time!).
> 
> Are we talking about the same thing here?
> 
> I was referring to the unbiased purely stochastic version of radiosity, which
> was a significant change to the algorithm; I was under the impression that this
> wouldn't end up in main POV-Ray in the form it was implemented in UberPOV. Maybe
> I missed something, is this in v3.8 now, or are you referring to improvements to
> sampling alone?
> 

Ah. This I do not know for sure. I am using the 'latest' v3.8-beta2, and 
as far as I can remember, the use of the stochastic implementation there 
is identical(?) to what was implemented in UperPOV. I am afraid this is 
all I can remember from those days, back in 2014, if I am correct. Using 
+am3 automatically switches on the stochastic render and I suppose 
(wrongly maybe) that this directly influences the radiosity, but if this 
then is a [quote] unbiased purely stochastic version of radiosity 
[/quote] I do not know indeed. This would need the comment of an expert 
(Christoph Lipka! where are you?). All I know is that it works fine 
as-is, and I have been using it ever since with v3.8-beta or v3.8-beta2.

Sorry for not being able to be more specific. :-[

-- 
Thomas

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The revision.txt file for v3.8-beta2 has this about stochastic renders:


------------------------------------------------------------------------------
POV-Ray v3.8.0-alpha.9841009
------------------------------------------------------------------------------

Commit 8c1eb72b on 2018-09-17 by Christoph Lipka

     Add anti-aliasing mode 3 (port from UberPOV).

     Also add some bits of infrastructure for future optimization and better
     co-operation of various stochastic features like jittered area lights,
     jittered media sampling, subsurface light transport and the like.


Hope this helps.

-- 
Thomas

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Thomas de Groot <tho### [at] degrootorg> wrote:
> The revision.txt file for v3.8-beta2 has this about stochastic renders:
>
>
> ------------------------------------------------------------------------------
> POV-Ray v3.8.0-alpha.9841009
> ------------------------------------------------------------------------------
>
> Commit 8c1eb72b on 2018-09-17 by Christoph Lipka
>
>      Add anti-aliasing mode 3 (port from UberPOV).
>
>      Also add some bits of infrastructure for future optimization and better
>      co-operation of various stochastic features like jittered area lights,
>      jittered media sampling, subsurface light transport and the like.

Ah yes I think this is just the stochastic sampling, not the modified radiosity
algorithm as a whole. I'm sure it improves things considerably but I don't think
it's what I was referring to!

That said, I should probably try out 3.8 at some point and see what's new for
myself :)

Bill

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