Am 31.01.2013 09:19, schrieb scott:

>> - It doesn't properly handle the variation in specular reflection
>> depending on incoming angle and ior (modeled by the "fresnel" setting
>> for reflections).
>
> Do you mean the specular reflections for point light sources controlled
> by the specular keyword? Or the specular reflections you get by using
> the reflection and power parameters (which the fresnel setting has an
> effect on)?

I mean the fresnel stuff in general: At low angles there is a lot of 
specular reflection. That reflected light obviously won't enter the 
material to be scattered diffusely. At high angles, however, the 
specular reflection is significantly lower, so more light enters the 
material to be scattered diffusely.

Neither POV-Ray nor MCPov honor this effect when computing the diffuse 
stuff.

>> - MCPov gets diffuse reflections wrong by a factor of 2.
>
> Can I correct for this by simply halving the diffuse factor in the
> finish statement?

To the contrary, you'll need to set the diffuse factor twice as high in 
MCPov.

>> - When using a "brilliance" setting of something other than 1.0, the
>> value specified in "diffuse" is /not/ the percentage of light scattered
>> back diffusely. Instead, the "diffuse" parameter directly controls the
>> brightness of the brightest spot. The new "albedo" keyword takes care of
>> this discrepancy: If you specify "diffuse albedo X", then X is indeed
>> the ratio of light scattered back diffusely (of all the light that comes
>> in).
>
> OK, I've not played about with brilliance before - but I assume albedo
> is not part of mcpov.

No, indeed not.

>> As you can see there are still some details missing for physically
>> realistic materials. But I'll keep working on it.
>
> Do you have an idea how much work it is to get mcpov type rendering into
> 3.7? Currently I use a simple program that fires off multiple mcpov
> instances and then merges the results, which works ok but obviously it
> doesn't take advantage of all the other goodies in 3.7.

It's not a thing to pull off in a week or so, that's for sure. I have 
already thrown together a patch that does blurred reflections, but 
blurred refractions are still missing, and I haven't yet fully 
integrated it with the other stochastic (or could-be-made-stochastic) 
elements already in POV-Ray (focal blur, anti-aliasing, area lights, 
diffraction and SSLT come to my mind). Importance sampling is still 
missing as well. It also doesn't render the image over and over again 
until you're satisfied - instead it uses a special oversampling mode 
that uses stochastic analysis of the rendered pixels to decide when to 
stop working on a render block and move on to the next one.

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