Re: [Gnome-print] Universal binary file format

[Lauris Kaplinski <lauris ariman ee>]

On Tue, 18 Apr 2000, Morten Welinder wrote:

> 
>    - As I understood, it is designed to be platform independent, i.e.
>    interchangeable between computers. But can anybody give me some examples,
>    for which uses this can be useful? Not spooling - this is more lowlevel.
>    Is that for bonobo?
> 
> Saving previews, and bonobo.  Spooling too, if printer queue manager and
> printing program are different.

Then we'll start having compatibility problems - what if a program creates
gnome-print-metafile-1.2, but renderer can handle only 1.1? Current format
does not allow it to skip unknown commands, so it has simply give up -
thing I hate with most commercial programs/file formats - they refuse to
open file which contains only one bit information they cannot handle.

>    Example: I tried to use metafile for temporary rendering - but
>    unfortunately it refuses to render before buffer is closed. Marking buffer
>    length without closing ended with 'serious metafile corruption' error.
> 
> Well, don't do that then.  Sure, the error mesage isn't great, but
> once you fix your program, all is fine.

OK - that means I have to implement additional buffering context, to save
graphics commands into - which I can replay at arbitrary moment, not only
after closing.

>    'AIFF''GPMF'{metafile size}'VERS'{string length}"Gnome Print Metafile 1.2"
>    'PAGE'{size of page description}'MOVE'{8}$x$$y$'LINE'{8}$x$$y$
>    etc. (I have to look more closely to spec - this is only as I remember it)
>    'ABCD' is four-byte designator
>    {number} is 32 bit integer (HSB first)
>    $number$ is 32 bit float (IEEE standard)
> 
> I don't see that we would be gaining anything.  We would (a) lose
> independence of integer size, (b) end up with too little floating
> point precision to render right.

The actual format of integers/floats can be different. Important point is
the possibility of skipping unknown chunks.
Other points:
- IFF also handles embedding (printing metafile inside metafile does not
require replying it).
- There are free IFF loading/saving libraries at least in Amiga worlds, so
instead of implementing every new binary format ad hoc, it would be nice
to reuse these.
- GnomePrint is probably not the only part of GNOME requiring flat binary
file format - other projects would benefit for standardization

etc. etc.

Regards,
Lauris