Am 17.08.2012 20:28, schrieb Dave:
> I built pov 3.7 rc6 beta on my Raspberry PI.
>
> The first time I built, openexr was enabled by default; the second time
> I built with '--without-openexr'. For each build I ran povray on the
> biscuit.pov file as done by 'make check'. Perhaps this is by design, but
> when built with openexr, the 8-bit color PNG exhibits weird artifacts. I
> would expect to see this if I used '+fn16' (I actually used +fn) and
> pnginfo displays the same info for both PNG's:

This is definitely /not/ by design; whether you build with openEXR or 
not should be irrelevant unless you actually try to use openEXR in- or 
output.

The only reason I can think of why disabling openEXR /does/ make a 
difference is that it is a file format based on some special 
"half-precision" floating point data type; maybe enabling openEXR also 
causes the CPU's floating point module to be switched into a different 
mode, where some computation errors become more prominent.


Are you sure the ARM does support full double-precision IEEE floating 
point arithmetics?


> For you information, when I first got the Raspberry PI up and running, I
> ran an ancient program 'paranoia.c' which tests floating point accuracy.
> The program can still be found here:
>    http://www.netlib.org/paranoia/paranoia.c
> The program reported no abnormalities on the Raspberry PI, so I would
> expect that the PNG's produced by both x86 and arm (--without-openexr)
> would be >close< to identical. But they are not...?

I have no idea what that program actually tests - not to mention that 
you might have compiled it with totally different floating point mode 
settings.

Post a reply to this message