On Tue, 10 Dec 2002 21:38:07 +0100
"Philippe Debar" <phd### [at] wanadoobe> wrote:

> You mean: I should not adjust the luminosity of the sky with your
> code, but leave it wholly independent? I plan to have one day a
> "scientific" Y to lumen conversion and hence have a real integration
> with your system. In the meanwhile, I wanted the luminosity to be
> dependant both on Intensity_Mult and on Exposure.

  No, I mean to not involve here the Lumens value. The overall scene
luminosity can still be controlled with EXPOSURE, and the sun/sky
intensity (lumens) with Intensity_Mult. That is, I can setup Skylight
ith Intensity_Mult to have an intensity proportionally correct respect
to the other lightsys lights, changing the overall luminosity of both
at once with EXPOSURE. 

 If you come up with a way to convert Y to Lumens, that would be
aditionally nice, because sun/sky intensity will be automatically
proportional to the lightsys lights (if you feed them with realistic
lumens values, of course).

> > (((lct/REF_WHITE)+(<COLOR_FILTER.gray,COLOR_FILTER.gray,COLOR_FILTE
> > R.gr ay>-COLOR_FILTER))*EXPOSURE)
>
> It looks very logical. I'll think about it. If anybody test this, I'll
> be happy to hear their thoughts.

  At least, the change to the "gray vector" on the color filter seems
necesary to get proper results: I changed it too for the next version of
my light macros (I've not tested it, but I'm supossing it was a bad
assumption for my part on float to vector promotion, or something...).

> It's not that complicated, really. It looks like it is, but it really
> is mathematical formulas copied from the paper into SDL.

  That is exactly what I was refering to: these papers are usually for
people who understand maths. 
 
> Many thanks. But once again: the merit is Preetham's.

  Yes, but you have the merit of being good enough, both at the SDL and
color maths, to port such "crude" scientific papers.
 
> >   1) The skydome texture is based on a luminous finish, with
> 
> Yes, it is because I designed it to use with radiosity, to get
> realistic lighting.
> 
> Furthermore, with diffuse 0 ambient 1 (and no highlights) it looks the
> same whatever the light sources in the scene are, which was my goal.
> With diffuse 1 (and I suppose ambient 0), it is dependant on the scene
> lighting. I did not test it that way, so I had no idea the results
> would be good, but I am really happy to learn it :-)

 Hmmm... I suppose you're saying that you don't want ths sky being
lighted with radiosity? Yes, that seems logical, as it changes the
exact colors calculated by Skylight, and the model is then not accurate.

 But, on the other hand, the POV docs encourage to use global ambient
set to 0 for radiosity with light sources, wich is what I do usually, to
use predefined and existant textures wich have ambient (rather than
changing all the textures to set ambient to 0). What's the solution in
that case? I can't think of anything right now... 

> I bet it is diffuse 1, which makes the sky colors dependant on the
> lighting, so the difference in orientation of the polygons shows.

  You're right! And don't worry: "brilliance 0" solves partially the
problem.:) Still, it's not the correct method to use your include,
because the sky gets excesively bright. I suppose it can be solved
decreasing the overall luminosity and decreasing the weight of the
sun... will try this too. 

  Next time I will post a first WIP for the scene where I'm using
Skylight.inc... regards.


-- 
Jaime Vives Piqueres
		
La Persistencia de la Ignorancia
http://www.ignorancia.org

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