#!/bin/bash
# Based on: https://gist.github.com/XVilka/8346728

awk -v term_cols="${width:-$(tput cols || echo 80)}" 'BEGIN{
    s="/\\";
    for (colnum = 0; colnum<term_cols; colnum++) {
        r = 255-(colnum*255/term_cols);
        g = (colnum*510/term_cols);
        b = (colnum*255/term_cols);
        if (g>255) g = 510-g;
        printf "\033[48;2;%d;%d;%dm", r,g,b;
        printf "\033[38;2;%d;%d;%dm", 255-r,255-g,255-b;
        printf "%s\033[0m", substr(s,colnum%2+1,1);
    }
    printf "\n";
}'

#!/bin/bash                                                                                                                                                                                     
# This file was originally taken from iterm2 https://github.com/gnachman/iTerm2/blob/master/tests/24-bit-color.sh                                                                               
#                                                                                                                                                                                           
#   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()                                                                                                                                                                            
{                                                                                                                                                                                           
    #printf '\x1bPtmux;\x1b\x1b[48;2;%s;%s;%sm' $1 $2 $3                                                                                                                                        
    printf '\x1b[48;2;%s;%s;%sm' $1 $2 $3                                                                                                                                                       
}                                                                                                                                                                                           

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 -1 128`; 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 -1 128`; 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 -1 128`; 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 -1 128`; do
    setBackgroundColor `rainbowColor $i`
    echo -n " "
done
resetOutput