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List:       kfm-devel
Subject:    loading GIFs
From:       Stephan Kulow <coolo () itm ! mu-luebeck ! de>
Date:       1997-07-12 21:11:13
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Hi guys!

After trying to implement animated GIFs, I've noticed a problem with
this. If khtmlw finds an image tag, it asks kfm (kioslave?) to get
this into the filesytem. After this is uses QPixmap:load and depends
on the installed filters. 
The problem is, animated GIFs aren't a pixmap, they're many of them!
For everybody not knowing that much about animated GIFS, I tell you
something about it:

GIF89a is a stream format. It starts with the usual header and a
(optional) global colormap. After that there are endless frames 
(usual is one :-), they are loaded til a sign ';'. So, it's really
possible to create infinite GIFs, there isn't a number of them in
the header. They come one after one. And I've seen such things in 
the web, but this would crash the mechanism of reading in the file-
system. To be understood right: I don't mean the loops, animated GIFs
do almost ever, this is an invention of Netscape and this you can see
in an animated GIF as an block 'NETSCAPE2.0' :-), but this isn't de-
fined in the GIF89 standard. A frame is optional a colormap, some
information (below) and the normal datas, that are used in GIF87 too.
That's the reason, why single GIFs are usual GIF87!
The information for one frame is:
1. how long the gap after this frame is (in ms, but netscape uses
 another factor for this, never messured exactly)
2. the offset (vertical and horizontal). You can define a animated
 GIF (also a normal infact), that is 800x600, but has only data for
 20x20.
3. of course, you can define interlace/non-interlace for every frame
 separatly
4. what should happen, if the frame disappear. It can be cleared with
 the background (usual the defined one in the GIF, but netscape uses
 the one of the HTML page). It can be replaced by the frame before or
 it can be not handled (that means, frame by frame)

Ok, hope you have a short overview about this topic. What we need is
a structure, that describes the GIF. If it loops (how often, if), the
size and the frames as QPixmaps with the informations.
I've mailed Taj yesterday about this topic, since he is the expert
for image filters, but didn't recieved an answer yet, so perhaps he
don't know :-), but I'm hardly sure, that this can't be solved with
QImageIO. 
The other problem is the mechanism with kioslave. Isn't it possible to
create IPC to transfer the pics while they're loaded? Or even emiting
signals, if some data arrived from the HTTP server. Correct my, if I'm
wrong in this topic, I hadn't a hard look at kioslave. And related to
this, I think, we must drop the mechanism with QImageIO, but I'm not
sure about that, since I've read in the QT documentation, that QImageIO
is ready for future extensions. I would volunteer to this async loading,
since I've done such thing at the university with QT for a MM project,
but I would like to discuss this first on this list, since this would
change this some things in khtmlw.

Please let me know, if I'm totaly wrong here or if you have comments
for this.

Greets, Stephan

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