I've placed a thin blue wall full of square holes in front of a white solid
wall, with a single light source to the left and above. The shadows I'm
getting don't make any sense at all.  Here's the code, plus a small .gif of
just the holes. With the light source as defined I'd expect the shadows to
be more or less uniform behind each hole.

This is just a test file - the original was more elaborate. That's where the
problem first cropped up. By the way, I'm using the Windows 3.1e version on
a Pentium 90, 64 meg/RAM.

Any help is appreciated.

Ken
--------------------------------------
camera
 {
  location <0,0,-60>
  direction <0,0,2>
  up <0,1,0>
  right <4/3,0,0>
  look_at <0,0,1>
 }

light_source {<-10000,10000,-45000> color White}

object
 {
  box {<-20,-20,0>,<20,20,0.1>}
  pigment
   {
    color White
   }
  finish
   {
    ambient 0.6
    reflection 0
   }
 }

object
 {
  difference
   {
    box {<-20,-20,-0.4>,<20,20,-0.41>}
    box {<-18,-1,-1>,<-16,1,1>}
    box {<-15,-1,-1>,<-13,1,1>}
    box {<-12,-1,-1>,<-10,1,1>}
    box {<-9,-1,-1>,<-7,1,1>}
    box {<-6,-1,-1>,<-4,1,1>}
    box {<-3,-1,-1>,<-1,1,1>}
    box {<0,-1,-1>,<2,1,1>}
    box {<3,-1,-1>,<5,1,1>}
    box {<6,-1,-1>,<8,1,1>}
    box {<9,-1,-1>,<11,1,1>}
    box {<12,-1,-1>,<14,1,1>}
    box {<15,-1,-1>,<17,1,1>}
   }
  pigment
   {
    color blue 0.4
   }
  finish
   {
    ambient 1
    reflection 0
   }
 }

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Attachments:
Download 'shadtest.gif' (2 KB)

Preview of image 'shadtest.gif'

Ken Kraft wrote:

> With the light source as defined I'd expect the shadows to
> be more or less uniform behind each hole.

The picture looks right (i.e. it looks how I'd expect it):
your lamp is almost infinitely away, causing the shadows to
be parallel images of the holes. OTOH, your camera is rather
close, thus the shadows (which are more far away from you than
the holes) seem smaller than the holes -- just as in the GIF.

If you want all shadows to look equal, put the lamp and the
camera into the same vertical plane parallel to the walls
(i.e. equal z for your orientation).

Ralf

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Ralf, thanks. You're right, that fixed it. It still seems counterintuitive.
In my example, the shadow behind the holes on the left look as expected, but
on the right it looks like the light source is to the right of the camera. I
suspect I need to visualize differently.

Ken

Ralf Muschall wrote in message <373B5DCF.6003874A@t-online.de>...
>The picture looks right (i.e. it looks how I'd expect it):
>your lamp is almost infinitely away, causing the shadows to
>be parallel images of the holes. OTOH, your camera is rather
>close, thus the shadows (which are more far away from you than
>the holes) seem smaller than the holes -- just as in the GIF.
>
>If you want all shadows to look equal, put the lamp and the
>camera into the same vertical plane parallel to the walls
>(i.e. equal z for your orientation).
>
>Ralf

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