Update scene files for best practice 3.7 onward gamma handling.

[wfpokorny]

http://bugs.povray.org/task/106

(Issue originally opened way back in 2011 and looks to have never been completely implemented. I argue strongly we not use conversion macros as suggested, but rather re-write where necessary for the cleanest presentation to new users. Our example scenes should represent best current practices, not forever compatible, historical implementations. -WFP)

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Details:

Most sample scenes and include files were designed at times when POV-Ray did not to any proper gamma handling, or still used the inferior 3.6 "assumed_gamma" mechanism.

All the scenes and include files should be reviewed, and updated to fit the new 3.7 gamma model.

The primary task will probably be gamma-adjusting literal color values and ambient parameters; I suggest using macros (which ideally should be defined in an include file) to be set according to the #version statement, so the scene/include file could be kept compatible with older versions.

[c-lipka]

All the scenes and include files should be reviewed, and updated to fit the new 3.7 gamma model.

Emphasis added because I think this is important - and also a problem, because existing scenes undoubtedly do rely on the old behaviour.

I think the best timing for such an update would be a larger version step, e.g. 3.7.x to 3.8.0; and even then we would need to make sure we provide backward compatibility somehow.

[c-lipka]

I think we really want to tackle this for v3.8.0, at least with respect to the scene files, and also the code snippets for the include menu. (The include files not so much, lest we break compatibility.) Therefore, I'm putting this on our plate for v3.8.0, to be tackled in the course of the beta phase.

I'm worried we might not find the time and energy though, so we may want to be open to reviewing this decision.