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<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN" "http://www.w3.org/TR/html4/loose.dtd">
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<html>
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<head>
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<meta name="GENERATOR" content="mkd2html 2.2.0">
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<meta http-equiv="Content-Type"
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content="text/html; charset=utf-8"> <link rel="stylesheet"
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type="text/css"
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href="../hint.css">
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<title>Best collaborative graphics</title>
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</head>
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<body>
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<h1>Best collaborative graphics</h1>
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<p>Etienne Duble<br>
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<a href="https://lig-membres.imag.fr/duble">https://lig-membres.imag.fr/duble</a><br>
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Twitter: @etienne_duble</p>
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<h2>Judges' comments:</h2>
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<h3>To use:</h3>
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<pre><code>make
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</code></pre>
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<h3>Try:</h3>
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<pre><code>./prog /tmp/drawing
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(open another window / terminal)
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./prog /tmp/drawing
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(open more terminals....)
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./prog /tmp/drawing
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</code></pre>
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<h3>Selected Judges Remarks:</h3>
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<p>After starting the program, use the cursor keys, then try some modes, like “p”
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or “l” (they toggle).</p>
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<h2>Author’s comments:</h2>
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<h3>Introduction</h3>
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<p>This program is a <strong>graphics editor</strong>, running on the terminal.</p>
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<p>It provides <strong>collaborative</strong> features: one can join the drawing session
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of someone else by just opening the same file!</p>
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<h3>Getting started</h3>
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<p>The program can run on Linux, FreeBSD, Mac OS X, and in most terminals.
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See section ‘Limits, Portability’ for more info.</p>
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<p>To build, type <code>make</code> (assuming gcc) or <code>make CC=clang</code>.</p>
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<p>Then you can start the program. It expects a file path as its first argument:</p>
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<pre><code>$ ./prog /tmp/drawing
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</code></pre>
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<p>(If not started this way, <code>prog</code> will refuse to start.)</p>
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<p>If the file does not exist, you will start with a blank drawing.</p>
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<p>If someone else (or another <em>instance of yourself</em>, maybe??) is already
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editing this file, you will join the session!</p>
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<h3>Edition features</h3>
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<ul>
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<li><strong>arrow keys</strong>: move cursor.</li>
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<li><strong>p</strong> key: enter <em>pen</em> mode (type <strong>p</strong> again to return to the default <em>move</em> mode).</li>
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<li><strong>l</strong> key: enter <em>line</em> mode (type <strong>l</strong> again to validate the line and return to the <em>move</em> mode).</li>
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<li><strong>c</strong> key: cycle through a small set of different <em>colors</em>.</li>
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<li><strong>q</strong> key: quit the editor. The drawing is automatically saved.</li>
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</ul>
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<p>The mode and current color is indicated at the bottom left corner of
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the editor.</p>
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<h3>Bonus features</h3>
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<ul>
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<li>If you just want to display the content of a drawing file, you do not
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need to start the editor. Just <strong>execute the drawing file</strong>: <code>./<the-file></code>.
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(This will fail if someone is still editing the file, though.)</li>
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<li><code>ls --color <drawing-files...></code> will probably select different colors
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to indicate whether a drawing file is being edited or not. :-)</li>
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</ul>
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<h3>Obfuscation</h3>
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<p>You will probably have a hard time analyzing this entry, because:</p>
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<ul>
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<li>Analyzing a system made of several communicating programs is known to
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be a complex task. (And if you think that observing a single-user drawing
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session will be a good starting point, read on.)</li>
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<li>Code coverage of single vs multi-user sessions is more or less the same. :-)</li>
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<li>Code coverage when using <em>move</em>, <em>pen</em> or <em>line</em> modes is almost the same.
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(so, is there a Bresenham algorithm somewhere??)</li>
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<li>Some OS resource values and stdlib call results are inferred.</li>
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<li>Whenever possible, variable names are reused.</li>
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<li>You might start analyzing escape code sequences right now, but warming up
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your brain is actually recommended. Start with a simple question such as:
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<em>in inverse video mode, will a space char show the foreground color or
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background color?</em></li>
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</ul>
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<h3>A few more things</h3>
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<p>Did you notice the <code>enum</code> declaration? Could it be just an <code>int</code> or <code>const int</code>
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variable, instead? (spoiler: http://c-faq.com/ansi/constasconst.html)</p>
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<p>If your keyboard has no arrow keys, you can probably find alternate keys by
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reading the source code.</p>
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<h3>Limits, Portability</h3>
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<p>I tested the program on several Linux systems, on FreeBSD 12, and on
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Mac OS X (mojave).</p>
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<p>On Linux, the program uses an OS-specific detail to hide communication
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artefacts, and avoids the need to remove them on exit.
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Since this is Linux-specific, it was not possible on FreeBSD or Mac OS.
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Its behavior is a little more <em>dirty</em> there.</p>
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<p>The program should work on most terminals that support 8-bit colors,
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inverse video mode, and movement escape codes, e.g. <code>xterm</code>, <code>gnome-terminal</code>,
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<code>terminator</code>, etc.</p>
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<p>Note: the drawing files <code>prog</code> generates are probably even more portable than
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<code>prog</code> itself!</p>
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<h3>Drawing area size</h3>
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<p><em>The drawing area size is set at compilation time</em>.</p>
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<p>The default size is the one of my xterm (see top of Makefile).
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You may set it to the full size of your terminal window by typing:</p>
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<pre><code>$ make fullscreen
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</code></pre>
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<p>IMPORTANT NOTES:</p>
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<ul>
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<li><strong>The program compiled with a given size will fail to reload a drawing file
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with a different size!</strong></li>
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<li>No scrolling is implemented (sorry but that would be too much for rule2!),
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so any peer reaching the session should have a terminal with the same
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size or larger.</li>
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</ul>
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<h3>prog.c vs prog.orig.c</h3>
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<p>The file <code>prog.orig.c</code> is the one I submitted.</p>
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<p>Judges proposed a small update: the program was using macro <code>FD_SET</code> inside an
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expression, which breaks compilation on Mac OS X. Wrapping this macro into a
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function was enough to fix this compilation issue.</p>
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<p>However, that was not enough to make the program work on Mac OS X. If you analyse
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the program you will see that it heavily relies on OS resources. And, for this
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first version of the program, you even needed to increase default <code>sysctl</code>
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parameters to make it work on FreeBSD (this was the purpose of file <code>check-os.sh</code>).
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I tried hard to tune Mac OS X the same, but failed.</p>
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<p>The simple fact Judges proposed this update meant they wish it could work on Mac.
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And if judges wish something, it <strong>has to</strong> be done. ;)
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So I refactored a little more the program to reduce OS resources consumption.
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Or maybe not reduce consumption, but consume them differently…
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And I obtained <code>prog.c</code>. With this version, no need to touch <code>sysctl</code> parameters,
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and it works on Mac OS X too!
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I must confess it was challenging to remain below the size limit with this little
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change.</p>
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<hr />
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<TABLE><TR>
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<TD><a rel="license" href="https://creativecommons.org/licenses/by-sa/3.0/"><img alt="Creative Commons License" style="border-width:0" src="/png/by-sa-3.0-88x31.png" /></a></TD>
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<TD><P>© Copyright 1984-2019,
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<A HREF="/judges.html">Leo Broukhis, Simon Cooper, Landon Curt Noll</A>
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- All rights reserved<BR>
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This work is licensed under a <a rel="license" href="https://creativecommons.org/licenses/by-sa/3.0/">Creative Commons Attribution-ShareAlike 3.0 Unported License</a>.</P></TD>
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</TR></TABLE>
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</body>
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</html>
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