Chambers wrote:
> BTW, here is another scene which attempts to replicate the problem using 
> reflection.  Not only does it show that reflection is not significantly 
> slower in 3.7, in some cases reflection is even faster in 3.7 than 3.6! 
>  So the bug is not directly related to recursive calls, but only to 
> transmittance.
> 
> ...Chambers

It gets even better.  I went back to the scene with the concentric 
spheres, and removed the IOR (so it's a bunch of transparent spheres, 
and nothing else).

Here are the old and new timings:

// Values using IOR
// Recursion 1: 1s; 4s; 4x
// Recursion 5: 2s; 15s; 7.5x
// Recursion 10: 4s; 29s; 7.25x
// Recursion 20: 9s; 1m 15s (75s); 8.3x
// Recursion 50: 37s; 5m 9s (309s); 8.35x

// Values NOT using IOR
// Recursion 1: 0s; 1s; -
// Recursion 5: 2s; 2s; 1x
// Recursion 10: 4s; 5s; 1.2x
// Recursion 20: 9s; 10s; 1.1x
// Recursion 50: 44s; 44s; 1x

As you can see, the 8x speed decrease is only observed when refraction 
(IOR other than 1.0) is used.  When no IOR is used, the speed is 
virtually identical.

...Chambers

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