[Radiance-general] Calculating diffuse component in a BRTDfunc

[atelier iebele abel]

Hi all,

I am writing a BRTD material which I want to use to change the diffuse 
component of a surface, related to a certain direction an the surface 
normal.
Radiance reports: error bad arguments for BRTDfunc
What am I doing wrong here?

I get the impression that the rfdif, gfdif, bfdif, rbdif, gbdif and 
bbdif are not variables ???
If these are not variables, how can I change/calculate/define the 
diffuse component in a BRTDfunc?
See the bold lines of the example in my cal file.

I appreciate any suggestions !

Iebele


<--- snip  ---->


{
    directional.cal

    arg10 red diffuse
    arg11 green diffuse
    arg12 blue diffuse
    arg13 direction x 
    arg14 direction y
    arg15 direction z
}

{ RGB values for the reflection  }
valr  = arg(10);
valg  = arg(11);
valb  = arg(12);
xdir = arg(13);
ydir = arg(14);
zdir = arg(15);

{ dot product direction and normal }
DdN = (xdir*Nx)+(ydir*Ny)+(zdir*Nz);

{ always return a positive value }
multi = if(DdN, DdN, -DdN) ;

*reflr = CrP + (multi*valr)  ;
reflg = CgP + (multi*valg)  ;
reflb = CbP + (multi*valb)  ;*


{
    example usage:
        void BRTDfunc LAYER114
        10
        0 0 0                          / reflection
        0 0 0                          / specular
        0 0 0          
        directional.cal
        0
        15
       * reflr reflg reflb              */ diffuse front*
        reflr reflg reflb  *            / diffuse back
        0 0 0                          / trans
        0.8 0.7 0.6                    / color of surface
        0.57735 0.57735 0.57735        / vector defining bright side of 
surface
}