Make isocontour transfer functions 'wrap'

[yt-fido]

Originally reported by: Nathan Goldbaum (Bitbucket: ngoldbaum, GitHub: ngoldbaum)

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Right now it's very difficult to come up with a transfer function that looks good on all scales. For example, in a zoom animation the transfer function needs to be very carefully chosen so it looks good throughout the zoom.

One possible way to fix this is to make the colormap periodic so that it 'wraps' around at the high end of the colormap.

This should allow scale-invariant zooms and time series visualizations with no foreknowledge of the simulation's dynamic range.

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• Bitbucket: https://bitbucket.org/yt_analysis/yt/issue/379

[yt-fido]

Original comment by Matt Turk (Bitbucket: MatthewTurk, GitHub: MatthewTurk):

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This might be an unpopular opinion, but I am -1 on this. I think I understand the objections -- and my data crosses 24 OOM in density, so I also worry about this -- but I'm not sure that a wraparound tf is the solution to that problem.

[yt-fido]

Original comment by chummels (Bitbucket: chummels, GitHub: chummels):

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Removing milestone: 2.4 (automated comment)