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.

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