Blender Git Loki

another trace commit

- implemented tracing of transparency for shadows. This is a material
option, in the new RayTrace panel.
it only traces color and alpha, not shading. So the results of some
transparant colored unlit faces can look odd. I will look onto that.
- changed fresnel formula (got hint from eeshlo!). this simplifies the UI,
now only one button needed. The fresnel value "should" be identical as
the refraction index, but that is booooring! So i added a special fresnel
refraction slider for both mirroring and transparency. By setting all 3
sliders equal, you get 'realism'.
- fresnel for transparancy works for Ztra rendering too. Same for transpa-
rent shadow. But then you need to set 'ray' on in F10 menu.
- uploaded new monkey_glass blend in download.blender.org/demo/test/

Next stage: killing the globals from render, and implement "translucency"
which is effectively allowing faces being lit from behind, as paper or
cloth.