#!/bin/sh -u
#   $0
# Draw a parabola on the terminal screen using cursor control.
# -Ian! D. Allen - idallen@idallen.ca - www.idallen.com

PATH=/bin:/usr/bin ; export PATH
LC_ALL=C ; export LC_ALL   # no internationalization in this script
LANG=C ; export LANG
umask 022

tput clear

width=80
num=20
y=$(( -num ))
while [ $y -le $num ] ; do
    x=$(( y*y ))

    # Calculate the display values of X,Y from the program values.
    # The display values must be non-negative and fit on terminal screen.
    #
    dispy=$(( y+num ))
    dispx=$(( x*width/num/num ))  # integer math: do multiplication before division

    # "tput cup" positions the terminal cursor on the terminal screen.
    # "tput cup" arguments have Y position first, followed by X...
    #
    tput cup $dispy $dispx ; echo -n '*'

    y=$(( y+1 ))
    sleep 0.1
done