scott schrieb:
>> There's one potential stumbling block: The "main loop", as I'd call 
>> it. In order to implement SMP this has changed quite a lot. 
>> Re-starting the render phase over and over again might not be as easy 
>> as it was in 3.6.
> 
> Once all blocks have finished in the current image, I wonder if you 
> could re-submit blocks again from the beginning to be re-rendered?  The 
> main loop code would have to deal with averaging the results rather than 
> just writing them to the screen/file.

That should be possible indeed. However, the render threads would have 
to be paused somehow while writing to the screen/file.

At any rate, I guess the problem can be solved, but it is the major 
obstacle to expect.

>> I hope, however, that whoever picks up that glove will not copy MCPov 
>> behaviour 1:1, as I recently found out that MCPov gets diffuse 
>> illumination wrong by what appears to be a factor of 2 in brightness.
> 
> Really?  What exactly do you mean by this (the whole scene is 2x bright, 
> but relative brightnesses are correct)? How do I check it?

Essentially, MCPov behaves like radiosity with a "brightness 0.5" 
setting, that is, diffuse illumination is attenuated by a factor of 0.5 
/per bounce/, messing with the brightness of shadows in relation to that 
of non-shadowed portions of the scene.

Initially I found out by comparing radiosity and MCPov results, leading 
me to the assumption that radiosity might be wrong in using a defailt 
brightness of 1.0; however, a carefully designed test revealed that 
brightness 1.0 is indeed the right setting to use, and that MCPov is 
doing it wrong; see news://news.povray.org:119/4b093e4b@news.povray.org 
in povray.unofficial.patches for details of the test setup.

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