Monday, February 17, 2014

Rainbow artifact

I found an interesting effect in Vue today. I noticed it before but never figured out what the problem was. On the picture below you can see a line running diagonally from top to bottom.






It turns out that this is an effect from the rainbow option in the atmosphere dialog. The artifact appears to be dependent on the position of the sun.

The scene itself is fairly simple, ground, sea, two trees, three very large rocks placed manually and about 250 rocks of three types in a global ecosystem.
Porous Stone
Ovis Stone
Oak Creek Stone

Memory used 15.4 GB.
Time to render 3 hours set at user.

One of the three rock types, and seen in the picture above, is 'porous stone'. After deleting these stones the rendering requirements was significantly reduced to about 30 percent and memory required is 6 GB.
It's still too slow for the scene considering it's simplicity, but it's much faster then it was. Clearly the Porous Stone was a significant drain on resources. No doubt the fractal displacement bump mapping is the culprit.
Other settings that effect the rendering time of this scene is likely:
 Sea is physically displaced.
Soft shadows on.
Soft reflections on.
The three large stones use a  Dax Pandhi material Supernoi, which is also a displacement map material, but is not as computationally expensive as Porous Stone.

Same scene with porous rocks and rainbow removed, sun lowered.

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