POV-Ray : Newsgroups : povray.binaries.images : hdr : Re: hdr Server Time
16 Oct 2021 18:26:52 EDT (-0400)
  Re: hdr  
From: Tek
Date: 12 Apr 2007 09:41:08
Message: <461e36f4$1@news.povray.org>
My light dome's not adaptive like that. I sample each light from an average 
of 20 points on the dome to get less aliasing, but for the light positions I 
just messed with some formulae until I got a nice even distribution of 
lights over the dome (I couldn't be bothered coding a geodisic dome light 
placement). My formula for spreading lights over a sphere is:

  #declare invpow = function(x,p) { 
select(x,-1+pow(1-abs(x),p),1-pow(1-abs(x),p)) }
  #while (i < num_lights)
   #local j=(i+.5)/num_lights;
   #local dir = 
vrotate(z,<invpow(j*2-1,.5)*90,invpow(j*2-1,.5)*sqrt(num_lights)*180,0>);
    ...place light...
   #local i=i+1;
  #end

To be honest I don't know why it gives such a good distribution, I found it 
by trial and error, I have a knack for messing with pow() functions until I 
get something that looks right!

Your weighted sampling technique sounds good, I assume you use bigger area 
lights if they're representing a region with less lights in (if you see what 
I mean). My area lights are setup so I can specify an angular size for them, 
which matches the region I'm sampling on the dome, the angular size was 
chosen using a simple sun-dial test scene adjusted until the distinct 
shadows overlapped enough that they looked like 1 smooth shadow.

-- 
Tek
http://evilsuperbrain.com

"Trevor G Quayle" <Tin### [at] hotmailcom> wrote in message 
news:web.461d485ac3e2923bc150d4c10@news.povray.org...
> First, thanks to the link to the HDRs, more to add to my collection!  (you
> can never hav enough in my opinion...)
>
> Second, looks pretty good.  Are you using any kind of weighted sampling? 
> A
> good weighting technique can reduce the number of lights needed to get 
> good
> results.  I have been working on a lightdome macro that creates 
> environment
> lighting from HDRs for quite some time now (not quite made it public, a 
> few
> more tweaks maybe).  Within the last month or so of development, I added
> area light support and found it worked out quite nicely.  With point
> lights, I was using about 256 (2^8) light sources with pretty good 
> results,
> but still had some artifacting visible depending on the probe used.  With
> area lights, I found I could get similar results, but with less 
> artifacting
> with as little as 32 (2^5) 3x3 area lights.
>
> I would like to see your scene perhaps to see how my lighting macro
> performs.
>
> If you need any further information on this, I'll see what I can do (I've
> been quite busy at non-POV lately, so have been here less frequently
> recently).
>
> I still hope to release my lighting macro at some point, I just have to
> convince myself that I'm satisfied with its operation.
>
> -tgq
>
>


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