Wolfgang Wieser wrote:
>>
>>What you describe seems to be specific to shadow rays, does your
>>suggested change also influence the appearance of the actual surface
>>(i.e. camera rays). You could try rendering with a fairly large accuracy
>>value for testing.
>>
> 
> Well, in iso code there is no difference between viewing and shadow rays. 
> The in_shadow_test flag is never actually used except for some cache 
> which is handeled at a higher level and should not matter here. 

So what?

My question was if your change makes a difference to the appearance of 
an isosurface despite possible effects on shadow ray tests.  This is 
best to test with high detail surface features of a size similar to the 
accuracy value.

>>I agree with Thorsten that the interpolation will probably cause
>>slowdown without much advantage 
>>
> 
> I am not sure about that. Because the gain in accuracy is considerably.

Note this is not a real gain in accuracy - it would be if the function 
value changed linearly between the two points but obviously it does not 
in most cases.  A comparitive test with raising accuracy and using your 
technique vs. current technique with low accuracy value would be necessary.

>[...]
> should work as well (and does for my scenes). All the other conditions 
> are just to work around conditions which I am not sure about. 

You should at least test with the most common special situations (use in 
CSG, view of the isosurface from inside, high gradient functions etc.).

Christoph

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