Le 18-04-16 à 19:29, Bald Eagle a écrit :
> "muyu" <lsy### [at] gmailcom> wrote:
>> I am simulating outdoor scene using radiosity. Regarding the light source, I
>> used one parallel light to simulate the beam. However, how could I simulate the
>> hemispherical diffuse radiation? Thanks in advance.
>>
>> Shouyang
> 
> Create a hemisphere (perhaps with an opaque flat back) and assign a light source
> to it.
> 
>  From the [F1] documentation
> 
> 3.4.3.1.7 Looks Like
> 
> By default a light source has no visible shape. The light simply radiates from
> an invisible point or area, however there are cases where this is not desired.
> Using looks_like is as an easy way to override this behavior. There is an
> implied no_shadow so that light is not blocked by the object, without it the
> light inside a non-transparent object could not escape. The object would, in
> effect, cast a shadow over everything.
> 
> When using looks_like there are a few important things to consider:
> 1.the object should be positioned at the origin
> 2.it's generally easier but not necessary to declare the object beforehand
> 3.works with point and spot lights not parallel lights
> 4.use a union instead if you want the object to block light and remember to make
> some portion of the object transparent
> 
> See the following examples:
> #declare My_Lamp_Shape = sphere { <0, 0, 0>, Some_Radius }
> 
> // using looks_like
> light_source {
>    <100, 200, -300> color White
>    looks_like { My_Lamp_Shape }
>    }
> 
> // using union
> union {
>    light_source { <100, 200, -300> color White }
>    object { My_Lamp_Shape translate <100, 200, -300> }
>    }
Beter way in this case :
union {
   light_source { 0 color White }
   object { My_Lamp_Shape }
   translate <100, 200, -300>
   }
Create at the origin, THEN translate.
> 
> 

Did you actually read the question ?
He want to have a sky that contribute to the scene's illumination.

Last time I looked, looks_like do work with parallel. I often use that 
feature with parallel. It's only with shadowless that it /may/ not work.

The object's location is always relative to the light. The reason to 
place it at the origin : It's origin is it's parent light.

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