Am 16.04.2012 12:56, schrieb D103:
> Ok, problems. :(
>
> To generate a unique cloud map for each planet, I need to (among other things)
> load the image map and normal map.
>
>  From these, I need to take samples along the x and y axis, and I don't know how
> to do so. My first thought was the trace() function, but I don't know whether I
> can get trace() to return the colour of the intersection.
>
> Second problem, even if I can use trace(), this means that I have to have the
> colour_maps in the scene in some form or another, and as the cloud_map is
> partially transparent, this would mean that the other objects would appear in
> the final render. :(
>
> Perhaps I could get around this by using two scene files? Downside would be less
> convenience, but if it's the only way...

Remember that you need to pass a #declare'd (or #local) object to 
trace(). Note that trace() only probes this single object, and that this 
object isn't visible in the scene unless you also instantiate it with 
"object{MyObjectVariable}". You could use this to trace() a height_field 
of the image.

trace() is comparatively slow for your purposes though. Instead, a 
better alternative is probably to define a "pigment function", which you 
can then directly evaluate to retrieve the pigment's color at any given 
point. The "functions.inc" macro "eval_pigment" encapsulates this in a 
simple macro:

#macro eval_pigment(pigm, vec)
     #local fn = function { pigment { pigm } }
     #local result = (fn(vec.x, vec.y, vec.z));
     result
#end

You pass it the pigment and the point to be evaluated, and will get a 
color value. (This is one of the few exceptions where functions may 
return colors rather than scalars.)

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