Fill console with 24-bit RGB colored blocks/short free demo.

#!/bin/bash
# Fill console with 24-bit RGB colored blocks -- short free demo
# Copyright (c)2018/04/10, zebulon_fr
# License: Public Domain ;D
# ---------------------------------------------------------------
shopt -s checkwinsize
export COLUMNS
export LINES
XMAX=$[COLUMNS-1]
YMAX=$[LINES-2]

# Random bi-colored block
Random() {
  local Rf Gf Bf Rb Gb Bb
    # Random foreground RGB color
    Rf=$[RANDOM%256]
    Gf=$[RANDOM%256]
    Bf=$[RANDOM%256]
    # Random background RGB color
    Rb=$[RANDOM%256]
    Gb=$[RANDOM%256]
    Bb=$[RANDOM%256]
    # Bi-colored block: top=foreground color, bottom=background color
    echo "\e[48;2;$Rb;$Gb;${Bb}m\e[38;2;$Rf;$Gf;${Bf}m▀"
}

# Computed color from (X,Y)
Color1() { # X Y
  local Lines LastPixel LastColor X Y Yt Yb Pt Pb It Ib RGBt RGBb Rf Gf Bf Rb Gb Bb
  Lines=$[(LINES-1)*2] # with have 2 pixels in a block
  LastPixel=$[(COLUMNS*Lines)-1]
  LastColor=$[(256*256*256)-1] # 24-bit RGB colors -> 16777216
  X=$1
  Y=$2
  # We compute two lines at once -- 't' stands for Top, 'b' stands for Bottom
  Yt=$[Y*2]
  Yb=$[Yt+1]
  # Compute pixel indexes: 0 to LastPixel
  Pt=$[Yt*COLUMNS+X]
  Pb=$[Yb*COLUMNS+X]
  # Convert to color indexes: 0 to LastColor (16777215)
  It=$[(LastColor*Pt)/LastPixel]
  Ib=$[(LastColor*Pb)/LastPixel]
  # Convert indexes as hex values, which contains RGB we want
  RGBt=$(printf "%06x" $It)
  RGBb=$(printf "%06x" $Ib)
  # Extract R/G/B from hex -- foreground color
  Rf=$(printf %u '0x'${RGBt:0:2})
  Gf=$(printf %u '0x'${RGBt:2:2})
  Bf=$(printf %u '0x'${RGBt:4:2})
  # Extract R/G/B from hex -- background color
  Rb=$(printf %u '0x'${RGBb:0:2})
  Gb=$(printf %u '0x'${RGBb:2:2})
  Bb=$(printf %u '0x'${RGBb:4:2})
    # Bi-colored block: top=foreground color, bottom=background color
    echo "\e[48;2;$Rb;$Gb;${Bb}m\e[38;2;$Rf;$Gf;${Bf}m▀"
}

clear
for Y in $(seq 0 $YMAX); do
    # A line is made of two horizontal lines at once, of half top blocks '▀' :
    # - visible top block as foreground color
    # - invisible bottom block as background color
    S=''
    for X in $(seq 0 $XMAX); do
        # Add a bi-colored block to the line.
        # Swap the commented/uncommented 2 lines below, to get something really different ;)
        S+="$(Random)"
        #S+="$(Color1 $X $Y)"
    done
    echo -e "$S"
done
# restore default foreground/background colors
echo -en '\e[49;39m'
# Snapshot of Random() colored blocks, here: https://zupimages.net/up/18/15/u9af.png
# Snapshot of Color1() colored blocks, here: https://zupimages.net/up/18/15/svv4.png