> It does not guess, you tell it so. Because as I said, colors should be 
> normalized. If you want black you have to lower the diffuse amount.

Are we talking about a biased raytracer like POV-Ray, or a different 
algorithm? POV-Ray definitely doesn't require normalized colors (3.7 
beta and Mega-POV both support HDRI output).

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>> It does not guess, you tell it so. Because as I said, colors should be 
>> normalized. If you want black you have to lower the diffuse amount.
> 
> Are we talking about a biased raytracer like POV-Ray, or a different 
> algorithm? POV-Ray definitely doesn't require normalized colors (3.7 
> beta and Mega-POV both support HDRI output).

No I was just trying to point out a problem with mixing 
reflection_amount & co with colors in the tentative pseudocode. POV-Ray 
certainly has no need to normalize colors.

Thinking about it the easiest way would be to define all the amounts as 
colors with all components between 0 and 1, and run the algorithm for 
each color, rather than trying to treat all colors simultaneously...

-- 
Vincent

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"Warp" wrote:
>
>  If you average the diffuse and the specular reflection, the latter
> would get a red tint.

Sure, there will be a red tint no matter if you add them or average them but 
in both cases the red tint is so small that it's insignificant.

Remember that the specular reflection of a light source is *many* times 
brighter than the diffuse reflection of that same light source in that spot 
where the highlight appears. So the contribution of the red diffuse 
reflection is insignificant compared to the specular reflection - exactly 
like if you had added them together.

Remember to think in terms of high dynamic range and not brightness values 
clamped to a [0-1] range...

Rune

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Vincent Le Chevalier wrote:
> OK, let's say more physically correct then ;-) I don't know, something 
> that conserves energy, for a start :-)

Fair enough. Hey, does it get a prism right, defracting different colors 
by different amounts? That seems pretty fundamental and possible even 
without doing QED calculations.

-- 
   Darren New / San Diego, CA, USA (PST)
     Remember the good old days, when we
     used to complain about cryptography
     being export-restricted?

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Darren New wrote:
>  Hey, does it get a prism right, defracting different colors 
> by different amounts? That seems pretty fundamental and possible even 
> without doing QED calculations.
> 

I think you can manage that in much the same way POV does at the moment, 
yes... It's just more costly in terms of rays, of course.

-- 
Vincent

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Vincent Le Chevalier wrote:
> I think you can manage that in much the same way POV does at the moment, 
> yes... It's just more costly in terms of rays, of course.

Oh! I didn't even know POV handled it at all. :-)

-- 
   Darren New / San Diego, CA, USA (PST)
     Remember the good old days, when we
     used to complain about cryptography
     being export-restricted?

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Darren New wrote:
> Vincent Le Chevalier wrote:
>> I think you can manage that in much the same way POV does at the 
>> moment, yes... It's just more costly in terms of rays, of course.
> 
> Oh! I didn't even know POV handled it at all. :-)
> 
Actually you made me doubt whether it was in Megapov or POV-Ray, but 
there it is, in mainstream POV:

http://www.povray.org/documentation/view/3.6.1/415/


-- 
Vincent

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Vincent Le Chevalier wrote:
> Actually you made me doubt whether it was in Megapov or POV-Ray, but 
> there it is, in mainstream POV:

Kewl. Faked, but kewl. ;-)  When changing the IOR in an unbiased render 
automatically makes a spectrum, let me know. ;-)

-- 
   Darren New / San Diego, CA, USA (PST)
     Remember the good old days, when we
     used to complain about cryptography
     being export-restricted?

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47266adb$1@news.povray.org...
> Kewl. Faked, but kewl. ;-)  When changing the IOR in an unbiased render 
> automatically makes a spectrum, let me know. ;-)

From what I gather from the Maxwell manual, materials use "full ior" data 
(ior for each wavelength) that are taken into account for dispersion. They 
even talk about a "performance hit" when using these, which must be 
something...

Frankly, the Maxwell demo is free (crippled at 800x600 with a watermark, but 
one can create, save and render scenes), available for Windows 32 or 64 
bits, OSX and Linux, and comes with a few test scenes. Lots of user-made 
materials are also available for free apparently. It's really worth the 
couple of minutes it takes to download it, if only to see how it works, and 
a little test drive would probably answer some of the theoretical questions 
I see in these threads.

G.

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>> You're still thinking in terms of a traditional ray-tracer with separate
>> diffuse and reflection components.
>
>  So does your algorithm you give below.

But it's flexible enough to allow you to insert any BRDF, just fire more % 
of rays in a direction towards the light than you do randomly scattered, 
following the shape of the BRDF.  In a traditional ray-tracer this is 
impossible, in the code below it is trivial.

>  That algorithm makes it impossible to render images like this:
> http://warp.povusers.org/images/sphere.png

Just change "surface_color" to some other variable, or even probably you'd 
want to use some function that gives a physically correct change from one 
colour to another depending on the angle relative to the light position.

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