Implementation notes

Glorious dot graphics.

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0. Concept

I spent the past few months playing Final Fantasy VI, which is a great
game in every respect, and it's also the last Final Fantasy before the
series moved into the 3D world.  I found those 2D dot graphics
absolutely charming and thought I had to share them.

Since this will be just low resolution dot graphics, I figured I will
just draw them in the terminal.  How hard can it be?

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1. Dot graphics

Drawing a single sprite wouldn't be so fun, I figured I will do an
animated sprite, in color.  I picked Tina's walking pose for this
purpose, which includes 9 unique sprites: 3 sprites for each of the
up/down/left directions, and the right direction sprites are obtained
by mirroring the left.  I added a 10th sprite (low HP pose) for when
the program terminates, because why not.

There are two technical details with this plan, the first is in
encoding and rendering of these sprites.  I thought the latter would
be a trivial application of ANSI control codes, except it turns out
approximating Tina using only 16 colors looks quite awful.  I can get
slightly more shades if I use Unicode characters U+2591 through
U+2593, but not every terminal supports Unicode.  What most terminals
(except Windows console) do support is ANSI with a 256 color
predefined palette, so that's what I went with.

For encoding the sprites, I developed a custom variant of LZW.  I
could have just gone with gzip+base64, but doing it this manually
means I actually have control over every byte in the final source.
This includes making all characters printable and excluding forward
slash characters, which turns out to be handy later.

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2. Interactive graphics

The other implementation detail has to do with reading input.  I could
have just let the program execute some kind of time-based loop, but it
would be great to get some keyboard interaction.  Normal console input
involves some press-enter-prompt so I would like to avoid that.  So I
sampled the list of usual programming languages installed on my local
machine, and turns out, Ruby is the only one that included a library
for reading raw console input one character at a time (via
"io/console").  I would need to install something extra for every
other language, so Ruby it is.  It also seemed oddly appropriate to
use a language named "Ruby" for something related to Final Fantasy.

But even with the convenient console library, Ruby doesn't seem to let
me do non-blocking IO.  Fortunately, it's easy enough to spawn threads
in Ruby, so I end up with a dedicated (blocking) IO thread that writes
to a global variable.  There is probably some thread safety issues
with that, but none that I care about.

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4. Testing

Tina has been verified to work in these environments:

- ruby 1.9.3p484 on Linux (putty)
- ruby 2.1.5p273 on Linux (xfce4-terminal)
- ruby 2.3.6p384 on Linux (xterm and gnome-terminal)
- ruby 2.3.6p384 on Cygwin (mintty)

For some environments such as "screen" or "tmux", you might need to
set the TERM environment variable to "xterm-256color" to make use of
the 8bit color palette.

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5. Finally...

The colors are slightly off and the IO thread felt like a hack, but by
the end of it, I got some nice dot graphics that I can view from a
distance, so I was really happy about it.

Really, the most difficult part about this program was simply finding
the time to write it.  What have I been doing for the past few months?
Wait, don't tell me...