FLTK GIF Animation

FLTK does not support loading/displaying animated GIF files currently. There has been already some third party work on this subject here:

KleineBre's FLTK stuff

Unfortunately there are many animated GIF's that don't play well with this solution. So I tried to fix the bugs, but after much disappointment decided to start from scratch. I found gif_load, an easy to use header only GIF loader to reduce the burden of decoding the GIF's to get more quickly (and safely) to the real work of designing the interface to FLTK.

Solution 1: External FLTK-Widget

My first solution was an external Widget Fl_Anim_GIF, derived from the basic FLTK widget Fl_Box. This solution works well and can be found in the folder extern.

But Kleine Bre's design approach to expand the Fl_GIF_Image class with animation capabilties seems advantegeous. But I did not want to have Fl_GIF_Image load animated files whithout being asked to and there was also a technical reason not to extend Fl_GIF_Image: Fl_GIF_Image converts the images to XPM format and the transparent color is always put at the first entry of the color table. This leads to problems when other frames of the GIF have a different transparent color index.

Solution 2: Replacement widget for current GIF class

So I came up with the idea to derive a class Fl_Anim_GIF_Image from Fl_GIF_Image that stores its images directly in RGB-format without an intermittent XPM.

This solution can be found in the folder intern:

The files there can be copied directly into the FLTK source tree to replace the current GIF code.

Fl_GIF_Image.cxx is basically the original FLTK widget with some minor necessary changes (e.g. default constructor).

Fl_Anim_GIF_Image.H, Fl_Anim_GIF_Image.cxx is the implementation of the animated GIF image class Fl_Anim_GIF_Image.

gif_load.h is the above mentioned GIF decoder, which is included from Fl_Anim_GIF_Image.cxx.

Current status as of 2019/01/10

The implementation is complete and works well. It has been tested extensively with all kind of GIF's - also with non-conforming and 'bad' ones.

It has been compiled/tested currently on Linux only, but should work on Windows too.

Some test programs are included in both solutions.

Both solutions offer roughly the same functionality:

• copy(), resize() with lazy (on-time) rescaling and usage of FLTK's (from version 1.4) fast image scaling feature
• color_average() and desaturate() methods
• it also possible to run several instances of the same animation simultaneously and to use it as tiles in Fl_Tiled_Image (internal solution only).
• application controlled playback possible

Current status as of 2023/02/19

Solution 2 (new FLTK Fl_Anim_GIF_Image class) has been incorporated into the official FLTK 1.4 source tree as of 2023/01/21 #2ddfd9d

This project will not be developed further.

It can still be useful as reference how to build an 'external' Widget as in Solution 1.

Building

[Note: instruction are for Linux]

There are two simple scripts in the root directory build-intern.sh and build-extern.sh that help to compile the test programs under Linux. Edit them to set your FLTK environment before running.

(Don't use them unless you understand what you are doing...)

The external solution produces these files:

• animgif: The full test program
• animgif-resize: A program to show live resizing animated GIF's
• animgif-simple: The "hello world" version for animated GIF's
• animgif-demo: A more practical demo to test the API

The internal solution produces these files:

• animgifimage: The full test program
• animgifimage-resize: A program to show live resizing animated GIF's
• animgifimage-simple: The "hello world" version for animated GIF's
• animgifimage-play: Demonstrates interacting with the class on single frame base

Test

You can test the different solutions with the test programs in each folder. For the internal approach you must have FLTK as source distribution to replace the mentioned files. Both solutions offer roughly the same functionality.

animgif/animgif-image:

Put images into the testsuite folder and display all of them by starting the test program with -t.

Or try the command line options for creating tiles, desaturate and color average.

Change the speed live using + and - keys.

Look at the minimal example programs to get a quick idea how to use the class.

Test the resizing programs to get an impression about speed and memory consumption.

Have a look at the API:

API of Internal widget Fl_Anim_GIF_Image

API of External widget Fl_Anim_GIF

Resume

I am not entirely convinced by the concept of the internal solution after all, but it is not bad either. On the one hand is cute to use it as a Fl_Image, on the other hand exactly therefore it seems inappropriate to put more and more playing functionality into it. The external solution so perhaps seems more advantegous after all..

Perhaps a generic Fl_Animation class (or whatever it may be called) would make sense - and one constructor for such a class could be an Fl_Animated_GIF_Image (which would then not be needed to run the animation, but only to supply the data). Or something like that.