in reply to Not a palindrom: a boustrophedon
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...
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.
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...).
For other ASCII-art animations, please refer to: