The improved Hosek / Wilkie model was added during my GSoC 2013 and the default since then.
The older model was kinda kept for compatibility, but after more than 2 years it's time to remove it.
The Hosek / Wilkie model is more realistic anyway, and people who really want a day / night transition can mix the Sky Shader with another one (e.g. color) and fade between the two.
This to avoids build conflicts with libc++ on FreeBSD, these __ prefixed values
are reserved for compilers. I apologize to anyone who has patches or branches
and has to go through the pain of merging this change, it may be easiest to do
these same replacements in your code and then apply/merge the patch.
Ref T37477.
* Added a new sky model by Hosek and Wilkie: "An Analytic Model for Full Spectral Sky-Dome Radiance" http://cgg.mff.cuni.cz/projects/SkylightModelling/
Example render:
http://archive.dingto.org/2013/blender/code/new_sky_model.png
Documentation:
http://wiki.blender.org/index.php/Doc:2.6/Manual/Render/Cycles/Nodes/Textures#Sky_Texture
Details:
* User can choose between the older Preetham and the new Hosek / Wilkie model via a dropdown. For older files, backwards compatibility is preserved. When we add a new Sky texture, it defaults to the new model though.
* For the new model, you can specify the ground albedo (see documentation for details).
* Turbidity now has a UI soft range between 1 and 10, higher values (up to 30) are still possible, but can result in weird colors or black.
* Removed the limitation of 1 sky texture per SVM stack. (Patch by Lukas Tönne, thanks!)
Thanks to Brecht for code review and some help!
This is part of my GSoC 2013 project, SVN merge of r59214, r59220, r59251 and r59601.
* Replaced the Preetham model with the newer Hosek / Wilkie model:
"An Analytic Model for Full Spectral Sky-Dome Radiance" http://cgg.mff.cuni.cz/projects/SkylightModelling/
* We use the sample code data, which comes with the paper, but removed some unnecessary parts, we only need the xyz version.
* New "Albedo" UI paraemeter, to control the ground albedo (between 0 and 1).
* Works with SVM only atm (CPU and CUDA).
Example render:
http://www.pasteall.org/pic/show.php?id=57635
ToDo / Open Questions:
* OSL still uses the old model, will be done later. In the meantime it's useful to compare the two models this way.
* The new model needs a much weaker Strength value (0.01), otherwise it's white. Can this be fixed?
* Code cleanup.
* Added a node to convert wavelength (in nanometers, from 380nm to 780nm) to RGB values. This can be useful to match real world colors easier.
* Code cleanup:
** Moved color functions (xyz and hsv) into dedicated utility files.
** Remove svm_lerp(), use interp() instead.
Documentation:
http://wiki.blender.org/index.php/Doc:2.6/Manual/Render/Cycles/Nodes/More#Wavelength
Example render:
http://www.pasteall.org/pic/show.php?id=53202
This is part of my GSoC 2013. (revisions 57322, 57326, 57335 and 57367 from soc-2013-dingto).
* Move hsv and xyz color functions into the dedicated util files (util_color.h and node_color.h).
* svm_lerp moved into util_math.h and renamed to lerp_interp, as it's used for the wavelength node now as well.
