#!/bin/bash -u
#   $0 [ word [ time ] ]
# Draw a parabola on the terminal screen using cursor control.
# Put out the word or a "*" if no word.
# time is total time to draw the parabola, top to bottom
# -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

word=${1-'*'}
time=${2-'2'}   # default 2 seconds

ss=( $(stty size) ) || exit $?
rows=${ss[0]}
cols=${ss[1]}
# divide the time by the number of rows to find rowsleep
rowsleep=$( dc -e "2 k $time $rows / p" )
width=$cols
margin=$(( width - ${#word} ))
num=$(( rows / 2 ))
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
    if [ $dispx -ge $margin ] ; then
	echo -n "*"
    else
	echo -n "$word"
    fi

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