Mike Williams wrote:
> Wasn't it Fjolsvit who wrote:
> 
>>This may be obvious, and I've simply overlooked it, but I can't seem to 
>>figure out a way to explicitly say what color I want at a specific point 
>>on a surface.  Basically what I want is a way to draw the u and v 
>>coordinate lines ...u = -2, u = -1, u = 0, u = 1, u = 2 ...,...v = -2, v 
>>= -1, v = 0, v = 1, v = 2 ..., etc.
>>
>>This *seems* like it should be easy.  Suggestions?
> 
> 
> If the object is one of those which supports uv_mapping, then you can
> use a uu_mapped pigment function something like this:
> 
> #declare Spacing = 20;                    
> sphere {0,1
>   uv_mapping 
>   pigment {
>     function {min(abs(sin(u*pi*Spacing)),
>               abs(sin(v*2*Spacing)))}
>     color_map { [0.0 rgb 0]
>                 [0.05 rgb 0]
>                 [0.05 rgb 1]
>                 [1 rgb 1]
>     }
>   }
> }
> 

Thanks.

It looks as though the answere is 'yes, and no'.  I wanted to do this 
with  a parameterized object or an isosurface.  *6.7.7.1 Supported 
Objects* of the docs is telling me I can't do it.  This *seems* somewhat 
strange since I am already defining the parameterized object in terms of 
UV parameters.  What I've done is to create a composite of areas 
excluding the coordinate line areas, and then create a union of all 
patches and coordinate lines.

This does not render very quickly, but it produces the basic desired 
result.  Now the next trick will be to draw an arbitrary curve on said 
surface.

<scratches head>

STH

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