[Bf-committers] Realistic materials question (Farsthary)

javier loureiro derethor at derethor.net
Wed Feb 25 13:34:52 CET 2009

I believe that the main problem with complex BxDF's is how to sample it
in an efficient way. There is no a way to sample according to a complex
BxDF (a tabulated one, for example) , so, you sample cosine weighted
around the normal. Also, you must define multiple leyers of BxDF for a
material, with different weights (like 20% diffuse, 60% phong, 20%
emissive), and "weight maps". The random number generation, and previus
stratification of samples is fundamental to sample correctly the whole

Another question: what happens when a material is emissive (like lava)..
how to deal with non realistic light sources, like point lights,
directional, etc?

pd. first time i write here :)

On Mon, 2009-02-23 at 15:18 -0500, echelon at infomail.upr.edu.cu wrote:
> Hi all :)
>  I've being making some researches and tests in the path tracer and as a
> result now are required fewer samples per pixel to achieve a desired
> level compared to my previous implementation. Off course , for pure path
> tracers that´s very dependant on the scene but in general are required 5
> times less samples.
>  A scene where before need 1000 spp now perform at similar level at 200 spp.
>  The algorithm handle very well diffuse surfaces, now is the time to
> tackle reflective and refractive surfaces and is where arise some
> questions:
>   Many small projects path tracers around the web are designed to work
> with a very specific BRDF model, or support only few BRDF
> implementations, but since the design of the Russian Roulette (if we
> want to account for those effects because pure statistics diminish small
> probability states like specular reflections ) should be tailored to
> certain parameters of a light scatter model, in order to design a
> general Russian Roulette I need to implement a physically based material
> with all the parameters needed for BxDF functions.
>   For example:
>   Blinn-Phong model------------>  kd + ks*(H.nor)^n have 3 parameters kd,ks,n
>   Modified Blinn-Phong model--->  kd/PI + ks*(n+2)*(nor,H)^n/(2*PI) also
> have 3 parameters
>  what I mean is what are the ever needed material properties for a BxDF
> model? here I'm very open to ideas, suggestions,papers,links and so :)
>  also I need good formulas for implementing tone mappers because path
> tracer images fall outside the (0,1) range.
>    Perhaps there´s already a well established plan for include physically
> based materials in blender in the future but I could not wait for that
> and although the Path tracer project could not became a candidate for
> official integration in the future it could ease the way for other
> projects so I should start implementing it in a very basic way :)
>                                    I´m waiting for help
>                            Cheers to all and thanks in advance
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