Sascha Ledinsky wrote:

> Is this also the reason why derivates are not supperted in POVMANs version
> of shader-language?
> 
No, true reason is my laziness :-)
But talking more seriously: Yes, this is one of reasons, why derivatives 
are not supported in POVMan: current implementation lacks information to 
support it. I have intention to provide some support for surface 
derivatives (for these objects, which support uv-mapping, although 
meshes are probably the only types, for which this uv-mapping is 
useful), but haven't had enough time for it :-(
I thought also about mip-mapping (or filtering of texture image file, as 
it is in RenderMan (BMRT) renderers), but this could be done only after 
surface derivatives are implemented. And I'm not quite sure, that this 
feature will make big difference with current supersampling (as Thorsten 
pointed out).

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