Trevor G Quayle nous apporta ses lumieres en ce 2008/01/29 01:13:
> "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
> 
> 
> 
1 - There are no coincident surfaces. The bottom box top is 0.01 unit lower than 
the edge of the dome.
2 - The artefact disapear if the bottom box is moved up until there IS a 
coincident surface.

-- 
Alain
-------------------------------------------------
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