On Tue, 30 Mar 2004 14:19:34 +0100, Phil Cook
<phi### [at] nospamdeckingdealscouk> wrote:

>On Wed, 17 Mar 2004 10:05:13 -0000, Phil Cook 
><phi### [at] nospamdeckingdealscouk> wrote:
>
>> On Tue, 16 Mar 2004 20:42:31 +0000, IMBJR <no### [at] spamhere> wrote:
>>
>> <snip>
>>> How odd. Unless I'm misreading the documentation, we should be able to
>>> do this. I'm sure I've see a classic Dark Side Of The Moon prism with
>>> refracted beam done in POV. I can't see why reflections should be any
>>> different.
>>
>> It was Tim Cook in p.b.i. 28/10/03 a refracting prism using a point 
>> light inside a sphere with a cut-out, and presumably a 
>> interior{dispersion}. If you switch off all the reflection on my 
>> LightReflector,  add a transparency or filter and switch back to the 
>> overhead view, the light beam does pass straight through and show up on 
>> the other side. However if you add 'refraction on' to the photon block 
>> it vanishes.
>>
>> It does seem strange to me, but again that may be to do with my 
>> ignorance in how this works, I'm sure someone else can answer this much 
>> better than I.
>
>Well I've gone through optics.pov which shows reflected beams etc., 
>unfortunately without explaining how it works, and pulled together the 
>following scene with comments. If anyone can offer an explaination why 
>both refraction and reflection need to be on in the light_source; why the 
>light_source must be outside the media container in order to get a 
>reflected beam; and why a cylinder light_source produces sharp edges in 
>the original beam with refraction on, I'd be most interested.

I shall look foward to having a poke at this.

>
>--
>Phil
>
>//code
>global_settings{
>photons{
>/*
>Photon count seems to be inversely linked to the radius of the cylinder 
>light_source
>smaller radius needs higher count
>*/
>count 150000
>media 100, 2
>}
>}
>
>/*
>This seems to be important as it appears that the light_source must be 
>outside the media
>so no global media allowed
>*/
>box{-20,20 hollow
>texture {pigment{rgbt 1}}
>interior{
>media{
>/*
>Note the higher rgb value and the extinction 0 to turn absorption off
>comment out extinction and beams vanish
>*/
>scattering{1,rgb 1 extinction 0}
>method 3 intervals 1 samples 4
>}
>}
>/*
>Without this no reflected beam
>*/
>photons{target}
>}
>
>/*
>Light source must originate outside media container
>switch to 10 and only original beam shows
>*/
>light_source{x*25, rgb<1.2,1,1.5>
>cylinder
>/*
>see photon count
>*/
>radius 0.5 //falloff 0.5
>point_at x*-10
>/*
>This is weird
>try
>photons{refraction on reflection off}
>photons{refraction off reflection on}
>photons{refraction off reflection off}
>Why does the reflected beam only show up when both are on?
>*/
>photons{refraction on reflection on}
>}
>
>camera{
>location y*10
>look_at 0
>}
>
>prism{-1,1,4
>0,<0,6>,<6,0>,0
>texture{
>pigment {color rgb 1}
>finish {ambient 0 diffuse 0 reflection 1}
>}
>translate <-3,0,-3>
>}
>//end code

--------------------------------
My First Subgenius Picture Book:
http://www.imbjr.com

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