hi,

when I put a blob inside a hollow glass object the colours of the
blob parts are no longer smoothly changed but switched somewhere
in the middle. the following input lines and the jpeg image (so they
are properly attached) show the effect by
comparing a blob inside and outside the glas object.

Do I make a mistake here?


many thanks in advance and best wishes from vienna

siegmar

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You made no mistake.  This is what appears to be a previously undiscovered bug
in POV-Ray.  I found the problem in POV's code: POV-Ray depends on a few global
texture and weight lists for multi-textured objects like blobs.  Unfortunately,
when it computes textures during shadow testing, it forgets to push the values
onto a stack and subsequently mangles the list.

Therefore, your temporary fix is to add the "no_shadow" keyword to the "merge"
object that the blob is in.  This will cause POV to skip the shadow test and
protect your blob's texture and weight lists.

   merge { 
      sphere { 
         <-0.5, 0., 0.> 
         C_VDW_Radius 
      } 
      sphere { 
         <0.5, 0., 0.> 
         C_VDW_Radius 
      } 
      texture { _T_VDW } 
      hollow 
      no_shadow // this will fix your problem
   } 

I'll tell the POV team about the bug and also how to fix it.

-Nathan Kopp

Siegmar Kardinal wrote:
> 
> hi,
> 
> when I put a blob inside a hollow glass object the colours of the
> blob parts are no longer smoothly changed but switched somewhere
> in the middle. the following input lines and the jpeg image (so they
> are properly attached) show the effect by
> comparing a blob inside and outside the glas object.
> 
> Do I make a mistake here?

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Great, it works fine. Thanks a lot!

I would never have found that solution myself.

siegmar

Nathan Kopp wrote:
> 
> You made no mistake.  This is what appears to be a previously undiscovered bug
> in POV-Ray.  I found the problem in POV's code: POV-Ray depends on a few global
> texture and weight lists for multi-textured objects like blobs.  Unfortunately,
> when it computes textures during shadow testing, it forgets to push the values
> onto a stack and subsequently mangles the list.
> 
> Therefore, your temporary fix is to add the "no_shadow" keyword to the "merge"
> object that the blob is in.  This will cause POV to skip the shadow test and
> protect your blob's texture and weight lists.
> 
>    merge {
>       sphere {
>          <-0.5, 0., 0.>
>          C_VDW_Radius
>       }
>       sphere {
>          <0.5, 0., 0.>
>          C_VDW_Radius
>       }
>       texture { _T_VDW }
>       hollow
>       no_shadow // this will fix your problem
>    }
> 
> I'll tell the POV team about the bug and also how to fix it.
> 
> -Nathan Kopp
>

Post a reply to this message