PC1 files created by Grafx2 can't be read by Degas Elite

[GoogleCodeExporter]

I don't know if this is part of some formal description of the PC1 format. But 
some PC1 loaders assume that each line can be unpacked individually. That is, a 
runlength must end where the line ends. This is how Atari ST applications such 
as Degas Elite does it. Obviously at the expense of the compression efficiency. 
But I guess maximum compatibility with archaic software is more important when 
it comes to the PC1 format.

(The same thing might apply to other RLE-based formats, but I havn't looked 
into it.)

Original issue reported on code.google.com by magnu...@algonet.se on 9 Jul 2013 at 3:13

[GoogleCodeExporter]

From looking at the docs (we have a copy here : 
http://code.google.com/p/grafx2/wiki/AtariFileFormats) the format clearly 
indicates it's forbidden to encode across lines, but I'm not so sure if it's 
also forbidden across the planes for a single line.

The code of Grafx2 seems to have the same restriction on loading and saving. 
IMO, if you know of some legitimate PC1 images that GrafX2 can't load, we 
should modify the loader to accept them. But even in this case, we should not 
modify the saving, because the resulting files can't be loaded in most 
PC1-reading programs.

Original comment by yrizoud on 12 Jul 2013 at 6:30

[GoogleCodeExporter]

I realize my description was not very clear. What I meant was that it seems 
Grafx2 (version 2.3.1780) DOES encode across lines. (There is nothing wrong 
with the loading code in Grafx2). Images created with Grafx2 cannot be loaded 
in, for example, Degas Elite on the Atari ST.

The problem can be replicated like this: Save an empty image in Degas Elite 
(empty-degaselite.pc1) and load it Grafx2. It works fine. Save it again in 
Grafx2 (empty-grafx2.pc1) and load it in Degas Elite. It bombs.

Original comment by magnu...@algonet.se on 13 Jul 2013 at 2:14

Attachments:

• empty-degaselite.pc1
• empty-grafx2.pc1

[GoogleCodeExporter]

Can you check if these files load correctly now ? I made same tentative changes 
that make the files look much more like the Degas Elite's one, though the file 
footer stays quite different.

Original comment by yrizoud on 29 Aug 2013 at 6:18

Attachments:

• nonempty-grafx2.pc1
• empty-grafx2.pc1

[GoogleCodeExporter]

Wait, I think I'm getting somewhere. XnView is kind enough to choke on every 
non-conforming file, and I think I'm starting to underdand the exact constraint.

Original comment by yrizoud on 29 Aug 2013 at 6:50

[GoogleCodeExporter]

I think it's fixed in r2063.
The PC1 document says "Elite uses a 40-byte buffer to store data being 
decompressed (...) The buffer is only emptied when there are EXACTLY 40 
characters in it.". Grafx2 was merely limiting RLE length to 39 (instead of the 
40 it was allowed - the empty file was longer than needed), now it is correctly 
ensuring that the commands end at byte 40, 80, 120, etc.
I've tested all the PC1 files here: 
http://samples.libav.org/image-samples/atarist/degas/
After re-saving them in Grafx2, XnView can now reload them fine. I attach them 
to this post, if you can test them in Degas Elite...?

Original comment by yrizoud on 29 Aug 2013 at 10:45

• Changed title: PC1 files created by Grafx2 can't be read by Degas Elite
• Changed state: Accepted

Attachments:

• PC1.zip

[GoogleCodeExporter]

About nonempty-grafx2.pci Degas Elite says "That is not a picture file!" 
(because it's actually a GIF file). Everything else work as expected. The 
palette cycling information (I know is present in the original version of 
magicmtn.pc1) is lost. But I assume that is not intended to be preserved. So, 
problem solved.

Original comment by magnu...@algonet.se on 30 Aug 2013 at 3:20

[GoogleCodeExporter]

Woops, sorry about the GIF. I just implemented the palette cycling for this 
format (and PI1), r2067. In many cases, the exact timing can't be preserved 
because GrafX2 (and Deluxe Paint) use a very different way of measuring speed 
than Degas Elite, but it's better than nothing. The case of magicmtn.pc1 is one 
that converts exactly in both direction : 2/60s Degas Elite == Timing "70" in 
Deluxe Paint & Grafx2

Original comment by yrizoud on 30 Aug 2013 at 5:29

[GoogleCodeExporter]

Original comment by yrizoud on 30 Aug 2013 at 5:29

• Changed state: Started

[GoogleCodeExporter]

Closing, as there is not much more to do here, issue is fixed.

Original comment by pulkoma...@gmail.com on 10 Feb 2015 at 8:27

• Changed state: Fixed