Short term TODO items (see webpage for the long term stuff):

URGENT
-------

- bug in heightfield - wrong orientation

- add all necessary arguments to turbulence

- fix uv.scm

- test outer volume materials - set ranges to all volumes (and voxel.c)

- transform-texture!

- test volumes with incoming light

- finish source docs

- test/integrate boundary normal table for hypers

- bug: hypers caching may result in false hit when hypers are
multiply instantiated

- test/integrate channels/spectral color

- test/enable trees to be used as CSGs

- enable table uv lookups for vertices of patches and tessels

- switch to guile-snarf building process

GEOMETRY
--------

- improve blob subdivision

- implicit surfaces - implement solver and triangulation, and use
IGNORE_SPHERE to store the sign of the last zero intersection

- remove isosurf

- add point-to-object-distance, allowing field displacement

- add explicit triangulation of all primitives

TEXTURES
--------

- cached textures

- make textures vary on rendering level

- forward RT of some sort

- mechanic simulations (fluids, particles)

ENGINE
------

- animation subdivision, motion blur

- parallelism support

- finish/integrate channels and spectral rendering

- XCF

- variable filtering
