Implementation notes

Eye-changing quine.

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0. Concept

I was so impressed by the turn of events in Durarara that I decided to
make an ASCII art for Sonohara Anri, the other main character.

I thought the most fitting function for this situation would be a
program that reproduces itself, similar to how Saika is able to
replicate itself in the minds of hundreds of people.  But it wouldn't
be any fun if I just made a straightforward quine, since I made quite
a few of those already.  So this time around, the output programs will
be slightly different from the original in that their eyes are
different.

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1. Layout data

The first step to writing a quine is to layout the different pieces of
data.  For this program, the different pieces are:

 - A "decoder" for outputting the source code.
 - The decoder encoded as a string.
 - Formatting data.

The decoder outputs the following:

 1. Some fixed header string.
 2. Encoded decoder.
 3. Formatting data.
 4. Decoded decoder data.

The formatting is stored using some run-length encoding scheme,
similar to quite a few other programs I have written in the past.
Basically:

 - ! = newline
 - * = glasses frames
 - # .. ) = eyes
 - , .. [ = space
 - ] .. } = non-space

Encoding of the decoder is a straightforward XOR 24.  To avoid
conflicts with whitespace and escape characters, this means characters
like "3", "8" and "g" can't be used in the decoder code, which is
easily worked around with a bit of arithmetic.

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2. Fill in code

Once the data layout has been decided, the final step is to write the
code.  Yes there are only two steps in writing programs like this,
it's trivial once you wrapped your minds the self-referential and
overlapping nature of the code.

Having said that, some techniques will make the two steps slightly
easier.
 - Write some proof-of-concept code first to verify that the data
   layout and the decoder works.  This can be found under v1 and v2
   subdirectories.

 - Use scripts to automate generation of the encoded and decoded
   portions of the source.  test.sh and the Makefile takes care of
   this bit.

 - Write the program backwards: format the last line first, and
   gradually work toward the middle where the encoded and decoded
   sources will meet.  This can be seen in image.txt: I wrote the
   second half of the program by hand, and the first half is generated
   automatically.

After the generated output has been verified to work, some manual
tweaking with the eyes are done to make sure that the "original"
anri.c will be different from all her children.

This program did not take that long to write relative to some other C
programs I wrote in the past, probably because I can now reduce the
while process to just 2 steps :)

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3. Finally...

The author wrote in the afterwords for volume 1: "I wonder how things
would go when the main character has nothing above her neck".  I can
tell you how headless main characters are -- they make terrible ASCII
arts.

Fortunately, the other characters are also very cool in different
ways.  Among the female characters, I liked Anri the best.  It's
either the sword or the glasses.