Hi, hope someone can help

I've modeled a bowl using sPatch and exported it in POV format. (it uses
'bicubic_patch'es)
I modified the file produced to use #declare to name the union object.

I then use
object { tray
  texture { T_Silver_5B }
}
and render.

Lovely...

except that when I shine a blue spotlight at the bowl from underneath
and place the camera on top, I see the floor of the bowl is blue (and
shows a shadow from a pipe placed beneath the bowl)

camera
 |
V
Bowl
pipe
^
 |
light

If I put the camera underneath, and look up, the floor of the bowl looks
the same.
I've sent some small (10k each) images.
Am I doing something wrong here?

Why can I see through my bowl?

David

PS For those who helped with the bendy pipes - here they are :)

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Attachments:
Download 'above.jpg' (12 KB) Download 'below.jpg' (12 KB)

Preview of image 'above.jpg'

Preview of image 'below.jpg'

Hi,

I not sure about this, but when I took a closer look at your bowl
especially in the second picture, I thought that the reflections might
cause the illusion of transparency. Maybe you should try a different
texture to confirm this. Just a suggestion.

Greetings

Marc

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Thanks for looking :)

The second picture is correct (or at least its what I expected!!)
You can indeed see a nice reflection of the pipe. You can also make out
the shadow of the pipe that is present on the upper picture.

The top picture has the problem.
How can I see the floor of the bowl?
There should be *no* light illuminating this surface at all!!
(The only light is a spot pointing 'upwards')
No there are no mirrors out of shot!! ;D
You should be able to see the outer wall of the bowl - thats fine.
And the lip where I curve the patches over, maybe thats too sharp and has
bicubic break-up.
But that shadow is too perfect and the floor's too evenly lit.
nb all bicubics have flatness 0.


I did try it with
pigment { Silver }
and got the same result.
I checked and the texture I used has no filters...

David

--
David Greaves

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David Greaves wrote in message <36138CC4.6E8891E4@telekinesys.co.uk>...

>The top picture has the problem.
>How can I see the floor of the bowl?
>There should be *no* light illuminating this surface at all!!


Not really. Only if the texture has an ambient value of 0.0 in its finish
(which the silver texture doesn't, I assume), wouldn't you see anything. See
"ambient" in the docs.

About the strange shadow/reflection: I don't know...

Johannes.

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Could you e-mail me ben### [at] btinternetcom (or post if you don't think the
others would mind) your source for this?  There's got to be a reason for
this somewhere ;)

Thanks,

Matt

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Johannes Hubert wrote:
> 
> David Greaves wrote in message <36138CC4.6E8891E4@telekinesys.co.uk>...
> 
> >The top picture has the problem.
> >How can I see the floor of the bowl?
> >There should be *no* light illuminating this surface at all!!
> 
> Not really. Only if the texture has an ambient value of 0.0 in its finish
> (which the silver texture doesn't, I assume), wouldn't you see anything. See
> "ambient" in the docs.
> 
> About the strange shadow/reflection: I don't know...
> 
> Johannes.

This sounds a lot like the problem mentioned in my earlier posting 
"Re: Tranlucency and bicubic patches".

In my sample code, I specifically made the ambient 0.0, and there
was no reflection value given (I assume the default is reflection 0?).
I tried to keep it as simple as possible, to eliminate the most likely 
sources of wierdness:

#declare myPatch = bicubic_patch {
   type 1 
   flatness 0.01 
   u_steps 3
   v_steps 3
     <0, 3,  1.0> <1, 2.5,  1.0> <2, 2.5,  1.0> <3, 3,  1.0>
     <0, 2, -0.5> <1, 2.0, -0.5> <2, 2.0, -0.5> <3, 2, -0.5>
     <0, 1,  0.0> <1, 1.0,  1.0> <2, 1.0,  1.0> <3, 1,  1.0>
     <0, 0,  2.0> <1, 0.5,  2.0> <2, 0.5,  2.0> <3, 0,  2.0> 
  translate <-1.5, -1.5, 0>
  texture {
     pigment {color red 1 filter 0}
     finish  {phong 1 phong_size 100 ambient 0 diffuse 0.9}
     }
   }

use a single light_source, just above the mid point between the camera 
and patch object, and have a look at it from several angles.

Lights and shadows are visible on the "wrong" sides of bicubic patches,
it seems, in both Mac and Win versions. Other things like clipped
objects
and discs don't display this feature/bug.

-jr-

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The posting of J.L. Rose made some points! There may be some kind of bug
(if that's what you want to call it) with the shadow and highlighting of
bicubic bezier patches. J.L's pictures prove this. 

At the moment the only workaround for this (that's easy when you are
working with sPatch) I can think of is to model closed hollow objects
that have a definite inside and outside. I have not experiencend any of
the above problems with my bicubic patch models and the only reason I an
think of is that I always create "closed" patch models.

This has surely one big disadvantage ... the number of patches rises and
makes rendering of complex models quite slow.

Any comment or idea is really welcome


greetings 

Marc

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I suspected this kind of bug with triangles some times ago : shadows and
lighting showing on the wrong side of triangles. But I actually have no
source for proving this.


I hope this does not un-help,

Povingly,


Philippe

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