in reply to Not a palindrom: a boustrophedon
Cet assombrissement est soumis au nom de Paris.pm canal assombri.
YES, BUT NO...
This program is in fact two programs. 966 characters divided by two: 483. Each of these program would fit nicely in 512 character. And tell me about inner beauty...
BOUSTROPHEWHAT?
This entry is based on a suggestion made to me by Stéphane Payrard: "Why don't you try a boustrophedonic form?", he asked. So I did. Since the term is defined in "The new hackers's dictionary", I had every reason to do so.
The first line of the program is actually a small "bootstrap" that read the rest of the file (here-document) and processes it before running the result.
SHOW ME SOME MORE!
Apart from using deprecated variables like $* ($# could have been put to more work, had I had more inspiration), the first line treats the program to eval differently depending on the presence of command-line arguments. If there are, the bootstrap evals the text without modification. Else, the program is treated as a boustrophedon, and every even line is reversed. (All that is done in the END statement at the beginning.)
The rest of it is a gross use of comments and qquoted strings, combined with the math needed for the fractals calculus and real to character screen- coordinates conversion. A few features were added to fill the last blanks, for example the use of the TPJ environment variable.
In interactive mode, the command are given in the following manner: for example, x.404y-.35703 w5 h 5 i 108z.9A-.3 a .3 n 100 the whitespace is optionnal (this is a difference with command-line parameters)
BEHIND THE SCENES: MATHS!
Here is the meaning of each command (and variable: each command is in fact a variable assignement):
- x: x-coordinate of the center of the screen (default: 0)
- y: y-coordinate of the center of the screen (default: 0)
- W: width of the output in characters (default: 79)
- H: height of the output in characters (default: 23)
- w: width of the printed screen (in real coordinates) (default: 2)
- h: height of the printed screen (in real coordinates) (default: 2)
- j: if non-zero, the printed image is the Julia set of parameter (x,y) (default: 0)
- X: x-coordinate of the center of the screen when displaying a Julia set (default: 0)
- Y: y-coordinate of the center of the screen when displaying a Julia set (default: 0)
- A: absolute rotation angle of the image (default: 0)
- a: relative rotation angle between the image and the next (default: 0)
- z: zooming factor between two images (default: 1)
- n: number of iterations for the calculus (default: 25)
- q: Quits the interactive program after next image.
STEP-BY-STEP
Line 1: The variable $00 is assigned the rest of the program's content,
and eventually modified in the end.
Line 2: The default values are affected.
Line 3: The batch program reads its command-line parameters and affects the
values.
Line 4: The interactive program creates its prompt (with each non-zero value
printed)
Lines 5-8: Part of the math for the iterations. Note that only half of the
lines are useful : the '#' splits them in two. (Line 8, it's the
second '#' that starts the comment.
Lines 9-11: The subroutine f contains all the necessary maths.
Line 11: The BEGIN at the end reads the values in the TPJ environnement
variable and puts them in @ARGV for processing by the program.
Please note that this BEGIN is executed after the previous END.
Line 12: s/// and y/// convert the prompt from garbage to human-readable
stuff. Thanks.
Lines 6, 8 and 10 are perfectly symmetric, which is some kind of waste of characters (imagine of much could have been squeezed out to fit into category 3...).
FURTHER ENJOYEMENT
For other ASCII-art animations, please refer to: