Christian Froeschlin <chr### [at] chrfrde> wrote:
> That "double_illuminate" thing has been popping up here
> often enough lately to overcome my activation threshold
> so I actually wished to try it myself ;)
>
> The left version uses no_shadow and I thought it looks
> rather ok, except that it should be brighter at the top
> where the lamp is open. The right version was an attempt
> to fix that using a semi-transparent pigment, but it
> doesn't look so great and I couldn't get it to emit any
> significant amount of light without saturating the lamp.

Hello,
  Neat shape!

Are you using radiosity in these images?  If you want the translucent surface to
emit light you'll need to use radiosity.

A few things I've picked up when experimenting with translucency and the
double_illuminate method which may or may not be useful to you.

1. Radiosity is almost always necessary.
2. For the outer surface to light up from the light source inside the shape, the
light has to hit the actual inside surface of the shape.  This is different than
a hollow shape carved out with a difference (which you may have done in these
images?).  A real hole in the middle of the shape will actually prevent this
method from working.
3. If the container shape has no holes (the light source will not spill out
anywhere directly) a point light will often work just fine.  The container
shape will serve to spread the light and soften the shadows (via radiosity). If
you want the light inside to have some shape to it (lighter and darker areas)
give it fade_power/fade_distance.   Leave them out for a more even effect.
4. If the container does have holes, you'll probably need an area light and
fade_power/fade_distance for it to look realistic.
5. Varying degrees of translucency in the surface can be simulated by varying
the diffuse value of the finish.  The higher the diffuse the brighter the
light, and the lower the darker.
6. Often its useful to make the container white, and let the light define its
color.  However this depends on the scene/effect you want.

What I've found works for a lampshade I've been working on was to just to take a
cone and use clipped_by to make holes in the top and bottom.  (First time I've
ever used clipped_by).  If you are using a lathe for your shape, the clipped_by
probably isn't even necessary; just don't cap off the ends in your spline.

I hope some of this is useful.

-The Mildly Infamous Blue Herring

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