24-bit-color.sh

#!/bin/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() {
  let h=$1/43
  let f=$1-43*$h
  let t=$f*255/43
  let 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