Blender Git Loki

* Volumetrics

Removed all the old particle rendering code and options I had in there
before, in order to make way for...

A new procedural texture: 'Point Density'

Point Density is a 3d texture that find the density of a group of 'points'
in space and returns that in the texture as an intensity value. Right now,
its at an early stage and it's only enabled for particles, but it would be
cool to extend it later for things like object vertices, or point cache
files from disk - i.e. to import point cloud data into Blender for
rendering volumetrically.

Currently there are just options for an Object and its particle system
number, this is the particle system that will get cached before rendering,
and then used for the texture's density estimation.

It works totally consistent with as any other procedural texture, so
previously where I've mapped a clouds texture to volume density to make
some of those test renders, now I just map a point density texture to
volume density.

Here's a version of the same particle smoke test file from before, updated
to use the point density texture instead:
http://mke3.net/blender/devel/rendering/volumetrics/smoke_test02.blend

There are a few cool things about implementing this as a texture:

- The one texture (and cache) can be instanced across many different
materials:
http://mke3.net/blender/devel/rendering/volumetrics/pointdensity_instanced.png

This means you can calculate and bake one particle system, but render it
multiple times across the scene, with different material settings, at no
extra memory cost.

Right now, the particles are cached in world space, so you have to map it
globally, and if you want it offset, you have to do it in the material (as
in the file above). I plan to add an option to bake in local space, so you
can just map the texture to local and it just works.

- It also works for solid surfaces too, it just gets the density at that
particular point on the surface, eg:
http://mke3.net/blender/devel/rendering/volumetrics/pointdensity_solid.mov

- You can map it to whatever you want, not only density but the various
emissions and colours as well. I'd like to investigate using the other
outputs in the texture too (like the RGB or normal outputs), perhaps with
options to colour by particle age, generating normals for making particle
'dents' in a surface, whatever!