Rename hint.txt and hint.text to README.md
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# Best collaborative graphics
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Etienne Duble
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<https://lig-membres.imag.fr/duble>
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Twitter: @etienne_duble
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## Judges' comments:
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### To use:
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make
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### Try:
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./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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### Selected Judges Remarks:
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After starting the program, use the cursor keys, then try some modes, like "p"
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or "l" (they toggle).
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## Author's comments:
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### Introduction
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This program is a **graphics editor**, running on the terminal.
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It provides **collaborative** features: one can join the drawing session
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of someone else by just opening the same file!
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### Getting started
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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.
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To build, type `make` (assuming gcc) or `make CC=clang`.
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Then you can start the program. It expects a file path as its first argument:
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$ ./prog /tmp/drawing
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(If not started this way, `prog` will refuse to start.)
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If the file does not exist, you will start with a blank drawing.
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If someone else (or another *instance of yourself*, maybe??) is already
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editing this file, you will join the session!
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### Edition features
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* **arrow keys**: move cursor.
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* **p** key: enter *pen* mode (type **p** again to return to the default *move* mode).
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* **l** key: enter *line* mode (type **l** again to validate the line and return to the *move* mode).
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* **c** key: cycle through a small set of different *colors*.
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* **q** key: quit the editor. The drawing is automatically saved.
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The mode and current color is indicated at the bottom left corner of
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the editor.
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### Bonus features
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* 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 **execute the drawing file**: `./<the-file>`.
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(This will fail if someone is still editing the file, though.)
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* `ls --color <drawing-files...>` will probably select different colors
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to indicate whether a drawing file is being edited or not. :-)
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### Obfuscation
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You will probably have a hard time analyzing this entry, because:
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* 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.)
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* Code coverage of single vs multi-user sessions is more or less the same. :-)
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* Code coverage when using *move*, *pen* or *line* modes is almost the same.
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(so, is there a Bresenham algorithm somewhere??)
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* Some OS resource values and stdlib call results are inferred.
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* Whenever possible, variable names are reused.
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* 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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*in inverse video mode, will a space char show the foreground color or
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background color?*
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### A few more things
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Did you notice the `enum` declaration? Could it be just an `int` or `const int`
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variable, instead? (spoiler: http://c-faq.com/ansi/constasconst.html)
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If your keyboard has no arrow keys, you can probably find alternate keys by
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reading the source code.
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### Limits, Portability
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I tested the program on several Linux systems, on FreeBSD 12, and on
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Mac OS X (mojave).
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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 *dirty* there.
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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. `xterm`, `gnome-terminal`,
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`terminator`, etc.
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Note: the drawing files `prog` generates are probably even more portable than
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`prog` itself!
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### Drawing area size
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*The drawing area size is set at compilation time*.
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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:
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$ make fullscreen
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IMPORTANT NOTES:
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* **The program compiled with a given size will fail to reload a drawing file
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with a different size!**
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* 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.
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### prog.c vs prog.orig.c
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The file `prog.orig.c` is the one I submitted.
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Judges proposed a small update: the program was using macro `FD_SET` 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.
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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 `sysctl`
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parameters to make it work on FreeBSD (this was the purpose of file `check-os.sh`).
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I tried hard to tune Mac OS X the same, but failed.
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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 **has to** 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 `prog.c`. With this version, no need to touch `sysctl` 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.
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--------------------------------------------------------------------------------
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<!--
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(c) Copyright 1984-2019, [Leo Broukhis, Simon Cooper, Landon Curt Noll][judges] - All rights reserved
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This work is licensed under a [Creative Commons Attribution-ShareAlike 3.0 Unported License][cc].
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[judges]: http://www.ioccc.org/judges.html
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[cc]: http://creativecommons.org/licenses/by-sa/3.0/
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-->
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