"ajm" <ajm### [at] aaogovau> wrote:
> Hi,
>
> Rendering a movie under beta 24 (Windows version, under Windows Server 2003 on a
> dual core Athlon), I noticed some random blocky brightness variations in parts
> of my scene viewed through a semitransparent object. The affected blocks vary
> from render to render (i.e. I get different results each time it renders).
> Checking with version 3.6, this doesn't happen. I've cut out and simplified
> enough of my source code to show the effect:
>
> camera { location <-30,10,5> look_at 0 angle 25 }
> light_source{ <-100,30,70> rgb 1 }
> difference { // make a dome
>   sphere { <0,0,0> 5 }  // ball
>   sphere { <0,0,0> 4.9 } // hollow interior
>   box { <-6,-6,-6> <6,1,6>  pigment { rgb 0 }}  // chop off bottom half
>   pigment { rgbt <1,1,1,0.675> }
> }
> box { <-6,-6,-6> <6,0.99,6> pigment { rgb 1 } } // sit it on a box
>
> The blockiness is visible mainly on the top surface of the box, viewed through
> the dome. Note that the effect disappears if:
>  - I remove the pigment from the box element used to cut off the bottom of the
> sphere
>  - I shift the lower box up a little till it touches the bottom edge of the dome
>
> While I can work around it easily now, I thought I'd bring it to the Beta team's
> attention.
>
> Cheers,
>
> Andrew.

http://tag.povray.org/povQandT/languageQandT.html#blackspots

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