gnome-control-center/capplets/screensaver/screensavers/attraction.xml

<?xml version="1.0" encoding="ISO-8859-1"?>

<screensaver name="attraction" _label="Attraction (balls)">
    <command arg="-root"/>
    <select id="mode">
	<option id="balls" _label="Balls" arg-set="-mode balls"/>
	<option id="lines" _label="Lines" 
	        arg-set="-mode lines" test="mode = lines"/>
	<option id="tails" _label="Tails" 
	        arg-set="-mode tails" test="mode = tails"/>
	<option id="polygons" _label="Polygons" 
		arg-set="-mode polygons" test="mode = polygons"/>
	<option id="splines" _label="Splines"
		arg-set="-mode splines" test="mode = splines"/>
    </select>
    <number id="threshold" _label="Threshold of repulsion" 
	    _low-label="Small" _high-label="Large"
	    low="0" high="500" default="100"
	    type="slider" arg="-threshold %"/>
    <number id="segments" _label="Length of Trail"
	    _low-label="Short" _high-label="Long"
	    low="1" high="1000" default="500"
	    type="slider" arg="-segments %"/>
    <number id="speed" _label="Speed"
	    _low-label="Slow" _high-label="Fast" type="slider" arg="-delay %" 
	    low="0" high="20000" default="10000"
	    from-cli-conv="20000 - var" to-cli-conv="20000 - var"/>
    <select id="use_color">
	<option id="color" _label="Full Color"
	        enable="number_colors,color_contrast"/>
	<option id="mono" _label="Monochrome" arg-set="-mono" test="mono"/>
    </select>
    <number id="number_colors" _label="Number of Colors"
	    type="spinbutton" low="1" high="400" default="200" 
	    arg="-colors %"/>
    <number id="color_contrast" _label="Color Contrast"
	    _low-label="Low" _high-label="High" type="slider"
	    low="0" high="25" default="3" arg="-color-shift %"/>
    <_description>Like qix, this uses a simple motion model to generate many different display modes.  The control points attract each other up to a certain distance, and then begin to repel each other.  The attraction/repulsion is proportional to the distance between any two particles, similar to the strong and weak nuclear forces.  

One of the most interesting ways to watch this hack is simply as bouncing balls, because their motions and interactions with each other are so odd.  Sometimes two balls will get into a tight orbit around each other, to be interrupted later by a third, or by the edge of the screen.  It looks quite chaotic.  

Written by Jamie Zawinski, based on Lisp code by John Pezaris.</_description>
    <fake name="Attraction (lines)"/>
    <fake name="Attraction (poly)"/>
    <fake name="Attraction (splines)"/>
    <fake name="Attraction (orbital)"/>
</screensaver>