Hi!

> > [bug] orthographic camera bug?
> > (objects sometimes disappear when the orthographic camera is used)
> > http://news.povray.org/3bdca5eb@news.povray.org
>
> An even simpler scene for this would really help.

I tried to simplify the scene as much as possible an here is the result:

camera { location <0,1,-1.481813> look_at <0,1,0> angle 30 orthographic}
sphere { 0,1 texture { pigment {color rgb 1}  }  }
sphere { <0,2,0>,1 }
sphere { <0,-2,0>,1 }

I removed as much spheres as possible and reduced the number of
texture statements. Normally you should see a dark gray sphere segment
on the bottom half of the image (maybe you have to turn up your monitor's
brightness), but due to this bug you get only an entirely black image.
I made some more experiments with the above example and found out
that the problem only occurs when:

*  camera points exactly in Z direction
*  camera type is orthographic
*  camera location z-value >= -1.481814 for an angle of 30 degrees;
   This value also depends on the size of the first sphere; The smaller the
   the sphere, the smaller the z value must be (e.g. -1.582 for size 0.9)
*  there are at least 3 objects in the scene
*  the vista buffer is enabled

The problem seems to be caused by the vista buffer. When disabling the
vista buffer by adding -UV to the options the problem disappears
entirely; With object counts lower than 3 the vista buffer seems to
be always disabled, so that's why you need at least 3 objects to
reproduce it.

Oh, I nearly forgot:
AMD AthlonXP 1700+, nForce Chipset, 256 MB RAM (224 MB + 32 MB shared)
Windows XP Home Edition (German), POV-Ray 3.5 beta9

Klaus.

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