Cody Boone Ferguson
3f59415c9d
Make lines beginning (in markdown files) 'BTW' bold. Rebuilt the respective html pages. Slight update to abstract in two entries (1985/shapiro and 1994/shapiro). One is changing 'defines' to '#defines' and the other was a typo fix. Fixed make gen_next: added missing new files. Various fixes in next/register.html (typos and other things).
277 lines
8.3 KiB
Markdown
277 lines
8.3 KiB
Markdown
## To build:
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``` <!---sh-->
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make
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```
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There is an alternate version, the original, which does not work well in macOS.
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See [Alternate code](#alternate-code) below if you are curious.
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### Bugs and (Mis)features:
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The current status of this entry is:
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> **STATUS: INABIAF - please DO NOT fix**
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For more detailed information see [2019/duble in bugs.html](../../bugs.html#2019_duble).
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## To use:
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``` <!---sh-->
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./prog file
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```
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## Try:
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``` <!---sh-->
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./prog /tmp/drawing
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```
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Open another window / terminal.
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``` <!---sh-->
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./prog /tmp/drawing
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```
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Open more terminals and repeat...
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You might also wish to try a full screen size. For this try:
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``` <!---sh-->
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make clobber fullscreen
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```
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Alternatively, if you want to change the size, do something like:
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``` <!---sh-->
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make clobber LINES=20 COLUMNS=20 all
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```
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The author provided us with the following table for use:
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<hr style="width:10%;text-align:left;margin-left:0">
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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*
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mode).
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* `l` key: enter *line* mode (type **l** again to validate the line and return
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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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After editing the file and quitting, try:
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``` <!---sh-->
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/tmp/drawing
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```
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i.e. execute the file.
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<hr style="width:10%;text-align:left;margin-left:0">
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WARNING: if the file is deleted it might lock any session still in use. These
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will have to be killed from another shell session or by closing the terminal tab
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(in other words don't do this from the console!). If the file cannot be opened
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in the beginning this will also happen. This is discussed in
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[2019/duble in bugs.html](../../bugs.html#2019_duble).
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**NOTE**: this entry might leave sockets lying about in the current working
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directory which you'll have to delete manually. This is also discussed in
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[2019/duble in bugs.html](../../bugs.html#2019_duble).
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## Alternate code:
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An alternate version of this entry, [prog.alt.c](%%REPO_URL%%/2019/duble/prog.alt.c), is provided. This
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alternate code might not work as well in macOS.
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### Alternate build:
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``` <!---sh-->
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make alt
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```
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### Alternate use:
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Use `prog.alt` as you would `prog` above.
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## 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 remarks:
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### Introduction:
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This program is a **graphics editor**, running in 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, macOS, and in most terminals.
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See section [Limits, Portability](#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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``` <!---sh-->
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./prog /tmp/drawing
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```
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(If not started this way, with a file, `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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### Edit 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.h` 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?
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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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macOS (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 macOS.
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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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``` <!---sh-->
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make clobber fullscreen
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```
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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](%%REPO_URL%%/2019/duble/prog.c) vs [prog.alt.c](%%REPO_URL%%/2019/duble/prog.alt.c)
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The file [prog.alt.c](%%REPO_URL%%/2019/duble/prog.alt.c) is the one I submitted.
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The judges proposed a small update: the program was using macro `FD_SET` inside an
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expression, which breaks compilation on macOS. 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 macOS. 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 the
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[check-os.sh](%%REPO_URL%%/2019/duble/check-os.sh) file). I tried hard to tune macOS the same, but failed.
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The simple fact the Judges proposed this update meant they wish it could work on
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Mac. And if the judges wish something, it **has to** be done. ;) So I
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refactored a little more the program to reduce OS resources consumption. Or
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maybe not reduce consumption, but consume them differently... And I obtained
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[prog.c](%%REPO_URL%%/2019/duble/prog.c). With this version, no need to touch `sysctl` parameters, and
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it works on macOS too! I must confess it was challenging to remain below the
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size limit with this little change.
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### NOTICE to those who wish for a greater challenge:
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**If you want a greater challenge, don't read any further**:
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just try to understand the program via the source.
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If you get stuck, come back and read below for additional hints and information.
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### For more information
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See <http://c-faq.com/ansi/constasconst.html> for more information.
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<!--
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Copyright © 1984-2024 by Landon Curt Noll. All Rights Reserved.
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You are free to share and adapt this file under the terms of this license:
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Creative Commons Attribution-ShareAlike 4.0 International (CC BY-SA 4.0)
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For more information, see:
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https://creativecommons.org/licenses/by-sa/4.0/
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-->
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