Ard nous apporta ses lumieres en ce 2005-06-24 00:55:
> I'm trying to render stage lighting using cylindrical light sources and
> environmental media.  Spotlights above a stage in a smoky bar, kind of
> thing.
> 
> The light sources are in the image, surrounded by objects that make them
> look like conventional spotlights, and the beams being emitted look
> fantastic as do the objects (musicians) they illuminate.  However the light
> sources look awful.
> 
> Here is a very simple example that exaggerates the problem.  The ends of the
> cylindrical lights are rendered as stark black discs.
> 
> camera {
>   location <0, 0.5, -1> look_at y/3
> }
> plane {-z, -1 pigment {rgb 1}}   // Backdrop
> plane { y,  0 pigment {rgb 1}}   // Floor
> // Illuminate the background so that the black discs at the ends
> // off the cylindrical lights are more obvious
> light_source {<10, 10 -10> rgb 0.3}
> // Blue light on left, aimed right, striking the floor:
> light_source {
>   <-0.5, 0.4, 0>
>   color rgb <0, 0, 5>
>   cylinder
>   parallel
>   radius 0.05
>   falloff 0.10
>   point_at <0.3, 0, -0.1>
> }
> // Red light aimed nearly at the camera
> light_source {
>   <0.1, 0.6, 0.5>
>   color rgb <5, 0, 0>
>   cylinder
>   radius 0.03
>   falloff 0.07
>   point_at <-0.05, 0.35, -1>
> }
> media { scattering { 2, rgb 1/2 extinction 0} }
> 
> I've various ways to replace the disks with illuminating objects, but they
> all look awful and I get the feeling I'm just missing something obvious.
> 
> Please set me right.  Is there a simple way to remove those black discs?
> 
> Many, many thanks in advance.
> 
> 
> 
A few solutions that I think of:
  - use spotlight instead of cylinder. You get conical beams, no black disks. Increase
the radius 
and falloff angles: 0.05 become 5
  - As you already have spotlight objects, just put a regular light_source _inside_ 
those objects. 
Don't use look_like. Make sure that the front end is actualy open. An advantage is
that you can have 
working bafles just like on real spotlights, enabeling you to have a shaped beam, not
just a 
circular one. If you want fuzzy edges, use an area_light with circular and orient (try
17*17 aray 
for smooth results) and keep the vectors short. Add adaptive 0 and increase if you get
artefacts 
(light spot in shadow or dark spot in lighted area)
You can combine those 2 suggestions: area_light spotlight.
If you get artefacts IN the beams, increase the samples value, DON'T increase
intervals!

Alain

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