24-bit-color-test

#!/usr/bin/env bash
#
#   This file echoes a bunch of 24-bit color codes
#   to the terminal to demonstrate its functionality.
#   The foreground escape sequence is ^[38;2;<r>;<g>;<b>m
#   The background escape sequence is ^[48;2;<r>;<g>;<b>m
#   <r> <g> <b> range from 0 to 255 inclusive.
#   The escape sequence ^[0m returns output to default

setBackgroundColor() {
  echo -en "\x1b[48;2;$1;$2;$3""m"
}

resetOutput() {
  echo -en "\x1b[0m\n"
}

# Gives a color $1/255 % along HSV
# Who knows what happens when $1 is outside 0-255
# Echoes "$red $green $blue" where
# $red $green and $blue are integers
# ranging between 0 and 255 inclusive
rainbowColor() { 
  (( h=$1/43 ))
  (( f=$1-43*h ))
  (( t=f*255/43 ))
  (( q=255-t ))

  if [ $h -eq 0 ]; then
    echo "255 $t 0"
  elif [ $h -eq 1 ]; then
    echo "$q 255 0"
  elif [ $h -eq 2 ]; then
    echo "0 255 $t"
  elif [ $h -eq 3 ]; then
    echo "0 $q 255"
  elif [ $h -eq 4 ]; then
    echo "$t 0 255"
  elif [ $h -eq 5 ]; then
    echo "255 0 $q"
  else
    # execution should never reach here
    echo "0 0 0"
  fi
}

for i in $(seq 0 127); do
  setBackgroundColor "$i" 0 0
  echo -en " "
done

resetOutput

for i in $(seq 255 128); do
  setBackgroundColor "$i" 0 0
  echo -en " "
done

resetOutput

for i in $(seq 0 127); do
  setBackgroundColor 0 "$i" 0
  echo -n " "
done

resetOutput

for i in $(seq 255 128); do
  setBackgroundColor 0 "$i" 0
  echo -n " "
done

resetOutput

for i in $(seq 0 127); do
  setBackgroundColor 0 0 "$i"
  echo -n " "
done

resetOutput

for i in $(seq 255 128); do
  setBackgroundColor 0 0 "$i"
  echo -n " "
done

resetOutput

for i in $(seq 0 127); do
  setBackgroundColor $(rainbowColor "$i")
  echo -n " "
done

resetOutput

for i in $(seq 255 128); do
  setBackgroundColor $(rainbowColor "$i")
  echo -n " "
done

resetOutput