Hi!

Simple (or not) question:

How to make (or simulate effect of) sth I call 'cylindrical radius light'
(probably wrong :)?

Imagine... standard light source placed in <0,0,0> between two infinite XY
planes, and distance between these planes is infinitely small. All rays of
light come radially from the point and are placed on XY plane.
Now add many of this light sources along Z axis, let's say: from z*-1 to
z*1.
Finally we've got 2 units long line of flat lights, placed in Z.

Object enlightened with this source will be in dark for Z over 1 or below
-1.
Shadow cast by this object will make on the {XZ translate -y*delta} plane
sth like cylindrical projection map used in carthography.

OK. It's simple: take two invisible planes (or two discs which is better),
place standard light source between them, scale/squish it, then make 10^n
copies of it along the line. Voila!

But performance will drop down dramatically, and I have no millenium to wait
for the effects.

Is there more simple way?


Regards
__________
 Gregor

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In article <web.3d931f0cf4969a7b6bd4eb880@news.povray.org>,
 "Gregor" <gre### [at] tvppl> wrote:

> But performance will drop down dramatically, and I have no millenium to wait
> for the effects.

So basically you want a light where the rays come out radially from and 
perpendicular to a line segment?
There's no fast way to do this without patching POV. It probably 
wouldn't be a very difficult patch, but you would have to convince 
someone it is useful enough. A better alternative would be some way to 
define this kind of thing in the scene file, using functions...somehow 
make the light position and intensity a function of the intersection 
point and other information. Really something that needs user-defined 
vector functions...which we don't have yet.

-- 
Christopher James Huff <cja### [at] earthlinknet>
http://home.earthlink.net/~cjameshuff/
POV-Ray TAG: chr### [at] tagpovrayorg
http://tag.povray.org/

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// bob's little test scene

// fill light (helps to visualize scene)
light_source
{
        y,0.25
}

sphere
{
        0,1
        pigment
        {
                color rgb <1,0.5,0.25>
        }
        translate <0,-1,5>
}

box
{
        -1,1
        pigment
        {
                color rgb <0.25,0.5,1>
        }
        scale 5
        translate <0,3,4>
}


/* light disk macro */
#macro
        CyLite
        (Thickness,Color,FadeDistance,Orientation,Position)
union
{
light_source
{
        Thickness*y,Color
        spotlight
        point_at -y
        radius 89.99
        falloff 90
        tightness 0
        fade_distance FadeDistance
        fade_power 1
}
light_source
{
        -Thickness*y,-Color
        spotlight
        point_at -y
        radius 89.99
        falloff 90
        tightness 0
        fade_distance FadeDistance
        fade_power 1
}
        rotate Orientation
        translate Position
}
#end


 // multiple disk lights
#local Count=10;

#while (Count>0)

/* Create the disk of light.
 Thickness, Color, FadeDistance, Orientation, Position */
CyLite ( 0.05, <1,1,1>, 10, <-5,10,-15>*Count, <1,-1,0>*Count/10 )

#local Count=Count-1;

#end

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On Thu, 26 Sep 2002 15:02:01 -0400, Christopher James Huff
<chr### [at] maccom> wrote:

>In article <web.3d931f0cf4969a7b6bd4eb880@news.povray.org>,
> "Gregor" <gre### [at] tvppl> wrote:
>
>> But performance will drop down dramatically, and I have no millenium to wait
>> for the effects.
>
>So basically you want a light where the rays come out radially from and 
>perpendicular to a line segment?
>There's no fast way to do this without patching POV. It probably 
>wouldn't be a very difficult patch, but you would have to convince 
>someone it is useful enough. A better alternative would be some way to 
>define this kind of thing in the scene file, using functions...somehow 
>make the light position and intensity a function of the intersection 
>point and other information. Really something that needs user-defined 
>vector functions...which we don't have yet.

It may be possible with some modifications to the SDL raytracer, but
it'll be sloooow.

/Erkki

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hughes, b. wrote:
>// bob's little test scene

Thanks, H.B., I've tried it. Nice trick, but... two comments:

A) There are TWO light sources for each stripe, and this slows down
raytracing much more than my 'light-n-disks-o-matic'.
B) There are funny looking effects of light/shade around ANY object placed
in the light cones. Strongly unacceptable.


So I've returned to my light-between-two-disks idea. Needs some
experimenting, but effect is good unless I try to aggregate those
flat-lights into cylinder. Even a hundred of them slows down everything to
infinity. And I need at least 1500-2000 parallel disks in my scene! And what
with media/photons/interior effects? Hell and devils!
Well, allrighty then. There'll be invented new
supercomputer of peanut size until mine POVray ends radiosity calcs!

Maybe much sparse (and fatter) disks'o'light with some kind of image_mapping
over the light_source? Is this possible in POVray? I know this method from
3DStudio.
And maybe some tricky use of parallel lightning in light groups?
I dunno.


If somebody'll find any simple solution to my problem - DO NOT hesitate to
post it!


Thanx
  Gregor


PS. I've got no enough experience to try user-defined vectoring so far, but
thanks for replies anyway - maybe later I'll try to use this clue.
__________
 Gregor

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