Hello,

Thorsten Froehlich wrote:
> 
> In article <36F8A917.83887EC9@ief.u-psud.fr> , LE COAT Francois
> <lec### [at] iefu-psudfr>  wrote:
> 
> > I compiled 3.1e version for ATARI platforms. But I have a problem.
> > When I generate PPM format, the R and B channel of the image seems
> > to be inverted. I looked at the ppm.c source code, and I can't
> > find the error. I precise that I used 3.1e for UNIX/LINUX and that
> > I use GCC 2.8.1. The all seems to work correctly. Maybe you have
> > a solution ... ATARI has 68k processors, and it's Big Endian.
> > Maybe the 3.1e version was adapted from 3.10 for DOS, and it
> > remains problems of Little Endian Intel's way. Can you help me ?
> 
> Hmm, I have never seen this behaviour on a Macintosh for both 68K and
> PowerPC versions. In general there is no (known) code in POV-Ray that
> requires adjustment for Endianes or has problems with it.
> Maybe your C library allows only output of 7 bit characters? However, then
> the other output formats shouldn't work either. Are you sure the program
> that views the image works correctly? In case you don't have another program
> to view the PPM I would suggest to post a small image that shows the problem
> for you in the povray.binaries.images group and ask there is someone can
> check it out.

In fact I discovered the bug. PPM is a UNIX file format. It begins with
texts information lines, and is followed by raw RGB image data. In fact
when in ppm.c my compiler (GCC) finds :
fprintf(fp,"P6\n");
that is the first magic identification of PPM files, it wrote to file
carriage return ('\015') followed by line feed ('\012'). Because PPM
is a UNIX file format, only CR should be written. Because there's a
LF after CR, it is interpreted as part of the RAW data. When I read
the file produced by POV, all the raw data are shifted. The portable
way of writing the previous C line would be :
fprintf(fp,"P6\015");
I suspect that the problem I encountered is not a specific 68k problem,
but it occurs on DOS versions, with DOS friendly compilers. It should
also occurs on MACS, because the control character is line feed
('\012').

Anyway, I corrected the ppm.c file, and the POV 3.1e PPM export is
now correct. Thanks for your suggestions. I verified that my viewers
(I have two) are correct.

Thanks for all,

Regards,

-- Francois LE COAT
Author of Eureka 2.12 (2D Graph Describer 3D Modeller)
WEB : http://eureka.atari.org

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