GifAnim Datatype

Introduction
============

The GifAnim v. 54 datatype is a subclass of (a helper for) the standard Amiga
OS4 animation datatype, which adds the ability to read and write animated GIF
files. When used with a program like MultiView or MultiViewer, it allows
animated GIFs to be played and optionally saved. When used with a program like
DTConvert (version 1.2 or newer), it allows other animation formats such as ANIM
and CDXL to be converted to GIF animations. And like any datatype it allows
objects, in this case GIF animations, to be embedded into a program, giving any
program the ability to display GIF animations with little effort by the
programmer.

The GifAnim v. 54 datatype was inspired by the 68K GifAnim datatype v. 2.5
written by Roland Mainz, which was ported to OS4 by Fredrik Wikstrom. But while
it was inspired by Roland Mainz' work -- which served as an invaluable reference
as to how to write an animation datatype, something that is not well documented
otherwise -- it was written from scratch, and does not use any of Roland's code.
Along the way, it fixed many problems with the older datatype.

The v. 54 datatype replaces the GIF file reading and writing code of the v. 2.5
datatype with that of GIFLIB, a widely used and well-debugged open-source GIF
file handling library. This maximizes the datatype's ability to handle all the
varieties of GIFs in the wild, and eliminates some of the crashiness of the
older datatype. The v. 54 datatype also fixes a number of bugs in the
compositing of the frames of a GIF file into a playable animation, which caused
the older datatype to play many GIF animations incorrectly. Finally, by
targeting only OS 4.1 FE (graphics.library v. 54) it disposes of all of the
ancient-compatibility kludges of the older datatype, including the need for
Cybergraphics when displaying truecolor animations.

Features
========

o Loads animated GIF files (those with two or more frames), which are then
   played by the animation datatype; single-frame GIFs are still handled by
   the regular OS4 GIF datatype

o Fixes many bugs in the v. 2.5 GifAnim datatype, eliminating crashes and
   allowing animations to play correctly

o LOOP option overrides the REPEAT setting of MultiView/MultiViewer,
   allowing GIF animations to loop without causing all other file types
   (such as sounds) to loop as well

o TRUECOLOR option converts GIF animations (which are always colormapped)
   into truecolor format for display; some GIF animations require this in
   order to display correctly

o Can save GIF animations to a new file, with optional optimization to
   reduce the size of the file

o When used with a utility like DTConvert, can convert any other
   (compatible) type of animation into a GIF animation

o Includes an installer that can also set the datatype's preferences

One feature of the v. 2.5 datatype that the v. 54 datatype does not support is
the ability to attach a sound file to a GIF animation. GIF files do not allow
for sound, so adding the ability to play sound was non-standard. The v. 54
datatype sticks to the GIF standard by not supporting sound.

Requirements
============

As the version number suggests, the GifAnim v. 54 datatype requires Amiga OS 4.1
FE (version 54) or newer. That's mainly because it makes use of version 54 of
graphics.library, which moves truecolor graphics support into the library,
eliminating the need for Cybergraphics and P96.

Source Code
===========

The GifAnim v. 54 datatype is open source; the source code is included.