[Radiance-general] Area lights breaking up?

[Ian Tester]

On Wed, 24 Aug 2005 08:27:00 -0700
Greg Ward <gregoryjward at gmail.com> wrote:

> (Meant to copy this to radiance-general, but I guess I missed.)
> 
> Hi Ian,
> 
> This behavior is the same as for Radiance 3.6.  (I just checked.)   
> You can increase the -dj parameter to 1 and get a better result.   
> Decreasing -ds also helps somewhat, but setting -ds 0 makes it look  
> unnatural.  Increasing the roughness also alleviates the problem --  
> it's just when you're on the boundary that you'll have trouble.
> 
> An alternative is to use a perfectly smooth material modified by a  
> random texture function that simulates roughness without applying the  
> BRDF model in Radiance, like so:
> 
> # A glossy surface
> void texfunc ball_roughness
> 4 gloss_dx gloss_dy gloss_dz gloss.cal
> 0
> 3 0.01 0.01 0.01
> 
> ball_roughness plastic white3
> 0
> 0
> 5       0.9     0.9     0.9
>          0.05    0.0
> 
> -Greg
> 
> P.S.  There are two relevant references for materials in Radiance, as  
> Rob mentioned:
> 
> SIGGRAPH '92:    http://radsite.lbl.gov/radiance/papers/sg92/paper.html
> 
> Materials reference:    http://radsite.lbl.gov/radiance/refer/ 
> materials.pdf

Thanks for that info. I tried your texfunc suggestion but it didn't seem to
be giving the effect I was after. Then I read about "plastic" in
materials.ps:

	If the surface roughness (a5) is zero or the specularity (rs) is
	greater than the threshold (ts) then a ray is traced in or
	near the mirror direction.

So I set -st to just below the specularity of the balls (0.05) and set
their roughness to the value I wanted (0.03). This gave a better effect and
seemed faster. I'm still using the texfunc modifier on a dielectric
material I need to match with the plastic (the transparent window over the
numbers on the billiard balls). So thanks for that.

bye