1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212
213
214
215
216
217
218
219
220
221
222
223
224
225
226
227
228
229
230
231
|
<!--startcut ==========================================================-->
<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 3.2//EN">
<HTML>
<HEAD>
<title>Xlock and Xlockmore Issue 18</title>
</HEAD>
<BODY BGCOLOR="#ffffff" TEXT="#000000" LINK="#0000FF" VLINK="#0020F0"
ALINK="#FF0000">
<!--endcut ============================================================-->
<H4>
"Linux Gazette...<I>making Linux just a little more fun!</I>"
</H4>
<P> <HR> <P>
<!--===================================================================-->
<center><img alt="Xlockmore" src="./gx/ayers/xlock.jpg"></center>
<center>
<H4>By Larry Ayers,
<a href="mailto:layers@vax2.rainis.net">layers@vax2.rainis.net</a></H4>
</center>
<hr>
<h3><center>Introduction</center></h3>
<p>Several years ago, in the dark backward and abysm of (computing) time,
Patrick J. Naughton collected several screen hacks and released them to other
Unix users as a package called Xlock. A screen hack is a clever bit of
programming which will display a changing image to the computer screen.
People felt vaguely guilty about wasting time writing these little programs
and gazing at the hypnotic, often geometrical patterns which they produced,
and thus the concept of the screensaver was born. The rationale was that if a
screen statically displayed text (or whatever) for a long period of time, a
faint imprint of the display would "burn in" and would thereafter be faintly
visible on the monitor screen. This actually did happen with early monitors,
but modern monitors are nearly impervious to the phenomenon (i.e, it would
take months). Nonetheless, the screensaver has survived, which is evidence
that its appeal ranges beyond the merely prudent and practical.
<p><a href="mailto: bagleyd@bigfoot.com">David A. Bagley</a> has become the
current maintainer of Xlock, which is now known as Xlockmore, due to the many
new modes included in the package.
<center><h3>Evolution</h3></center>
<p>Xlockmore can be thought of as a museum of screen hacks. The old Xlock
modes are all still included, and some of them (at least to this jaded
observer) aren't particularly impressive. On the other hand, there is a
certain haiku-like charm to certain of the older modes. The pyro mode, for
example, manages to convey something of the appeal of a fireworks display with
nothing more than parabolically arcing dots which explode just over the peak
of the trajectory.
<p>Over the years as computers have become more powerful the complexity of the
added modes has increased. Some of the newer ones are CPU-intensive and need
a fast processor to run well.
<p>David Bagley must be receiving contributed modes and bugfixes quite often,
as he releases a new version every couple of months. Some of the newer modes
are amazing to behold and take full advantage of modern graphics hardware.
<center><h3>OpenGL Modes</h3></center>
<p>I'm sure most of you have seen some of the OpenGL screensavers which many
Win95 and NT users run. Even though many of them advertise one product or
another, they tend to be visually compelling, with a three-dimensional and
shaded appearance. In the latest Xlockmore package the option is offered to
compile in several flashy new modes based on the Mesa OpenGL libraries.
<p><em>Gears</em> is an impressive Mesa mode: nicely shaded gears
turning against each other while the group slowly rotates.<br>
<p>
<img alt="Gears screenshot" src="./gx/ayers/gears.gif">
<hr>
<p>The <em>Pipes</em> mode, displaying a self-building network of 3D pipes, is
also OpenGL-dependent. Marcelo F. Vianna came up with this one. Luckily most
Linux distributions these days have prebuilt Mesa packages available.<br>
<p>
<img alt="Pipes screenshot" src="./gx/ayers/pipes.gif">
<hr>
<p>Ed Mackey contributed the <em>Superquadrics</em> mode, which displays
esoteric mathematical solids morphing from one to another. He also is
responsible for porting the <em>Gears</em> mode to
Xlockmore.
<hr>
<center><h3>Mathematical Modes</h3></center>
<p>Jeremie Petit, a French programmer, has written one of the most intriguing
"starfield" modes I've ever seen. It's called <em>Bouboule</em>, and if you
can imagine an ellipsoidal aggregation of stars... I really can't describe
this one well, and a screenshot wouldn't do it justice. It's appeal is in
part due to the stately movement of the star-cloud, somehow reminiscent of a
carnival Tilt-A-Whirl ride in slow motion.
<p>Another excellent mode which doesn't show well in a screenshot is
<em>Ifs</em>. If you have never seen Iterated Functions Systems images
(Fractint and Dick Oliver's Fractal Graphics program display them well) this
mode would be a good introduction. IFS fractals seem to have two poles: at
one extreme they are severely geometrical (Sierpinski's pyramid comes to mind)
and at the other, organic-looking forms which resemble ferns, shells, and
foliage predominate. The <em>Ifs</em> mode induces a cloud of particles to
fluidly mutate between various of these IFS forms. The result (at least to my
mathematically-inclined eyes) is often spectacular.
<p>The upcoming <em>Gimp</em> version 1.0 will include a
nicely-implemented plug-in called <em>IFS-Explorer</em>, which enables the
creation of IFS forms in an interactive fashion.
<p>Massimino Pascal, another Frenchman, wrote <em>Ifs</em>,
and as if that wasn't enough, he has contributed another math-oriented mode
called <em>Strange</em>. This one recruits the ubiquitous cloud of particles
and convinces them to display mutating strange attractors. They <em>are</em>
strange to behold, diaphanous sheets and ribbons of interstellar dust (or is
that subatomic dust?) twisting and folding into marvellously intricate
structures which <em>almost</em> look familiar.
<p>The eminent British physicist Roger Penrose invented (discovered?) a
peculiar method of tiling a plane in a non-repeating manner many years ago.
The Penrose tiling (as it came to be known) was popularized by several
articles by Martin Gardner in his Mathematical Recreations column, which
appeared in Scientific American magazine in the late sixties and seventies.
The tessellation or tiling is based on a rhombus with angles of 72 and 108 degrees. The
resulting pattern at first glance seems symmetrical, but looking closer you
will notice that it varies from region to region. Timo Korvola wrote the
xlock mode, and it can render two of the several variations of the tiling.
<p>An aside: recently Roger Penrose noticed the Penrose tiling embossed into
the surface of a roll of toilet paper, of all things. He previously had patented the
pattern, thinking that it might be profitably implemented in a puzzle game, so
now he has sued the manufacturer. It'll be an interesting and novel trial, I imagine.
<br>
<p>
<img alt="Sample Penrose Window" src="./gx/ayers/penrose.gif">
<hr>
<p>Another mathematical mode, very spare but elegant and pleasing to
regard, is Caleb Cullen's Lisa mode. This one displays an animated lissajous
loop which bends and writhes in a remarkably three-dimensional manner.
As with so many of these modes, a still shot doesn't really do it justice.<br>
<p>
<img alt="Lisa Window" src="./gx/ayers/lisa.gif">
<hr>
<p>The modes I've described are just a sampling of newer ones; the
Xlockmore package contains many others, and more are continually added.
<center><h3>Configuration</h3></center>
<p>Xlockmore is included with most Linux distributions and tends to be taken
for granted; the default configuration files for Fvwm and Afterstep (which
most users use as templates for customization) include root-menu items for
several of the older modes. I'd like to encourage anyone who has used
Xlockmore to take the time to download the current version (4.02 as I write
this). Not only because of the newer screensaving modes, but also because
compiling it from source allows you to easily tailor Xlockmore to your tastes.
<p>Here is the procedure I follow when compiling an Xlockmore release: first
I'll try to compile it "as is", just running the configure script and then
compiling it. If by chance it can't find, say, your X11 or Xpm libs, you may
have to point the Makefile in the right direction by editing in the correct
paths.
<p>If you are unfamiliar with Xlockmore, now is a good time to try out all of
the modes. The quickest way to run through all of them is to run Xlock from
an xterm window, with the following command line: <br>
<p><kbd>xlock -inwindow -mode [name of mode]</kbd>
<p>A window will open up with the mode displayed. Dismiss it with a left-
mouse-button click, press the up-arrow key to redisplay the command, and edit the
command for the next mode. Keep track of the ones you would rather not keep,
perhaps in a small editor window. There are three files which need to be
edited: the <b>Makefile</b>, <b>mode.c</b>, and <b>mode.h</b>. Just edit out
references to the unwanted modes (you can <i>grep</i> for the mode names to
find the line numbers). Recompile, and you will have a smaller executable
with only your selected modes included. You also will now be able to run
xlock with the <b>-fullrandom</b> switch, which will display a random mode
selected from the ones you chose to keep.
<p>Something to consider -- since at this point you have a compiled source
tree there on your hard disk, you might want to take a look at the source
files for some of the modes. In general, the <i>*.c</i> files for the various
modes are unusually well commented. If you are curious about the origin or
author of a mode, you'll find it in the source. There are often parameters
that can be changed, if you like to experiment, and some files can be altered
to suit your processor speed. A few modes even have entire commented-out
sections which can be uncommented and thus enabled. It may not work, but if
you save the original <b>xlock</b> executable before you start fooling with
the source you can always revert to it. An advantage of keeping a built
source tree while experimenting is that if you modify a single <b>C</b> file,
recompilation is quick as only the modified file is recompiled. After all, one
of the oft-touted virtues of Linux (and free software in general) is that
source is available. Why not take advantage of the fact?
<center><h3>Availability</h3></center>
<p>The source archive for Xlockmore-4.02 can be obtained from
<a href="ftp://ftp.x.org/contrib/applications/">ftp.x.org</a> or from
<a href="ftp://sunsite.unc.edu/pub/Linux/X11/screensavers/">Sunsite</a>.
<!--===================================================================-->
<P> <hr> <P>
<center><H5>Copyright © 1997, Larry Ayers<BR>
Published in Issue 18 of the Linux Gazette, June 1997</H5></center>
<!--===================================================================-->
<P> <hr> <P>
<A HREF="./lg_toc18.html"><IMG ALIGN=BOTTOM SRC="../gx/indexnew.gif"
ALT="[ TABLE OF CONTENTS ]"></A>
<A HREF="../lg_frontpage.html"><IMG ALIGN=BOTTOM SRC="../gx/homenew.gif"
ALT="[ FRONT PAGE ]"></A>
<A HREF="./e2compr.html"><IMG SRC="../gx/back2.gif"
ALT=" Back "></A>
<A HREF="./redhat.html"><IMG SRC="../gx/fwd.gif" ALT=" Next "></A>
<P> <hr> <P>
<!--startcut ==========================================================-->
</BODY>
</HTML>
<!--endcut ============================================================-->
|
