[Bf-cycles] Hair render settings

[Stuart Broadfoot]

Hi Brecht,
    Sure, if the `experimental' choice can be removed that would be great.
Most of the custom parameters are only useful for specific cases and are 
hardly ever used.

"I suggest to remove the Custom type,
and instead make the primitive a choice like this with further options
always visible:

* Primitive: Curve, Line, Triangle (low memory usage vs. speed)
* Shape: Ribbon or Cylinder (flat normal towards viewer or rounded)

I think that covers all the different types?
Except for the difference between Triangle Ribbons and Planes, which I don't 
really understand,
Planes seems to always look better to me so maybe just keep only that?"

- Yes, that would cover every type. The Ribbons are suppose to be like 
strips of paper that twist, while the Planes always face the camera.
My implementation of the ribbon generation needs improving. It can probably 
be completely removed for now.
The tessellated triangles option also needs to be improved.

"Further some other settings that could perhaps be simplified:

* Interpolation: can this use the settings in the Render panel or
replace it? There is already a B-Spline and steps, this seems
unnecessary."

- The interpolation settings are redundant. They were added when I was only 
exporting the hair keys and needed to interpolate between them.
Now the segments are exported into cycles this is not necessary.

"** Method: can this always be accurate?
** Exclude encasing: I'm not sure when this option helps, only found
missing shadows when using this."

- The extra methods are used to give slight speed improvements and most 
options aren't ever used by the presets.
The `exclude encasing' option is used to avoid errors when using the 
`uncorrected' method. If the methods available are reduced then this can 
probably be removed.

"** Use tangent normal as default / geometry: I think this could be
left to materials?"

- This option can be removed. It should be used whenever the shape isn't 
cylindrical and can be applied automatically then.

"* Triangles Planes Smooth option seems to do nothing. Think this could
always be enabled and removed anyway?"

- The `smooth' option is probably most notable when you have tessellated 
triangles.
I can't think of any situation where a user may want flat shading though and 
agree this can be removed.

"* Include Parents: the render panel already has a Parents option that
could be used?"

- This was also added quite early on for debugging and can be removed.

I will make those changes. The other controls that will still be there would 
be `Check back-faces', `resolution' and `curve subdivisions'.

Best,
Stuart