Animation

ePiX is ideally suited to the creation of mathematically accurate animations: If a figure depends suitably upon a ``time'' parameter, then a loop can be used to draw the entire figure for multiple time values, yielding successive ``snapshots'' of the figure as time progresses. The shell script flix automates the process of compiling a suitable input file into a collection of pngs and assembling these frames into a mng animation. ImageMagick is the image-handling engine.

A flix file is an epix file with two restrictions:

• The double variable tix is used as ``clock''.

• main accepts two commandline arguments and sets tix accordingly.

Jay Belanger's emacs mode recognizes the file extension .flx and inserts template code if an empty buffer is opened. Creation of flix files is as easy as creation of epix files. The directory samples/extras contains a handful of flix files that may be consulted for ideas.

A ``typical'' .flx file may take 30 seconds to a couple of minutes to compile. To present the impression that work is being done, flix prints a progress bar, counting the number of eps files that have been created. There will be a delay of a few seconds after the last frame is produced, during which ImageMagick's convert utility creates png files from eps files, then assembles the movie.

To facilitate debugging, elaps can be run on a flix file. elaps runs in a fraction of the time, and if elaps can't produce a viewable image, flix will surely fail.

By default, flix creates movies with 24 frames, in which tix runs from 0 to 1, and animates at $0.08$ sec/frame. Command-line options change these and other parameters; please use flix's built-in help for details.