On 12/15/2017 07:28 AM, Masaki  wrote:
> There are two things I want you to ask for a favor.
> 
> I want to make the light source, which is positioned randomly between y=0~1 and
> emits the light at the specific angle, 45 degrees. The light beam forms the
> conical surface.
> (Q1) Can I make this light source ?

I know of no built in way to strictly get a conical light source where 
all the rays are at 45 degrees relative to some light source axis.

Perhaps with photons and the right sort of lens system? Hmm... Wonder if 
something could be done with using radiosity where the bright object had 
an aoi pattern which gets bright only when the ray angle is very near 45 
degrees? Would depend upon geometry of your scene I suppose. Plus with 
the radiosity I question how well it might work with respect to 
radiosity's sampling.

Approximations are possible where the conical ring of light still 
spreads over distance from the point source as you are attempting.

> 
> I conceive that if the light through the torus (or the disk) is only rendering,
> the above requirement can meet. So, I write the source code as follows, but the
> pov-ray dose not work properly. It seems to be wrong with the "projected
> through" option.
> (Q2) What is wrong in my source code and how to  revise it ?
> 

Assuming you have a plane or other objects in your scene which will be 
lit, try changing your light source from:

  color 100000

to:

  color 1/number

I think it probable you are getting a result where everything is clamped 
to 'white' given your very bright light source has not been set up to 
fade as real lights do with distance. The light source might be too 
bright for your particular scene dimensions even with realistic light 
fading.

If I've guessed wrong as to the problem you see, please post a more 
complete scene with lit objects and more specifically what you think is 
not working. Note that given your largish torus minor axis dimension and 
relative point light position there will be significant light spreading 
and overlap.

Bill P.

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