Paint16b: A 16 byte paint program written in 12 lines

And something I found useful https://www.muppetlabs.com/~breadbox/software/tiny/teensy.ht...

It really is quite amazing how small you can make things when you try. Then you realise you're wasting most of a disc sector, and the thing you have is unportable and unmaintainable. But still, being able to look at a binary and know what every byte does, being unconstrained by the rules of a language is liberating.

http://stanislavs.org/helppc/int_33.html

http://stanislavs.org/helppc/int_10.html

The main loop contains an implicit state-machine that does multiple things on different iterations, which is partly responsible for the small size.

Another thing that you can clearly see is how efficient it is at using the registers; this is one area where compiler-generated code is consistently behind, and something I wish compilers would get better at --- an HLL could take as many bytes as this entire program just to put the parameters onto the stack and call a function.

Finally, one small correction:

    ret             ; assume [[FFEE]] = [0] = CD20 = int 20

either way cool! :D

Hmm. So the second time this program is run, it will fail?

  #!/bin/bash
  #
  #  Author: Martin "BruXy" Bruchanov, bruxy at regnet.cz
  #
  
  # Check input first
  if [ ! $# -eq 1 ] || [ "$1" == "-h"] || [ "$1" == "--help" ] ; then
  	printf "Usage:\n"	
  	printf "\t$0 saved_image\n"
  	printf "\n\tImage data will be saved into given filename, if file exist\n"
  	printf "\tit will be displayed and ready to edit!\n"
      printf "\tHit <Ctrl-C> any time to quit the program.\n"
  	exit 1
  fi
  
  ##################
  # Initialization #
  ##################
  
  IMAGE_FILE=$1
  _STTY=$(stty -g)    # Save current terminal setup
  printf   "\e[2J"    # clear screen, set cursos at beginning
  stty -echo -icanon  # Turn off line buffering
  printf "\e[?9h"     # Enable terminal mouse reading
  printf "\e[?25l"    # Turn of cursor 
  printf "\e]0;-=[ ShPaint ]=-\007"
  
  # Hash array with image data,
  # ... key is "$Y;$X",
  # ... value ANSI colors and brush "b;F;Bm"
  declare -A IMAGE  
  
  # Defaults
  BRUSHES=(       )
  FG=( {30..37} )
  BG=( {40..47} ) # 49 ... default background
  X=0 
  Y=0
  ERASE=0
  BRUSH=${BRUSHES[3]}
  FG_COLOR="1;${FG[7]}"
  BG_COLOR=49
  
  #############
  # Functions #
  #############
  
  function save_image() {
  	printf "\e[2J" > $IMAGE_FILE
  	for i in ${!IMAGE[@]}
  	do
  		printf "\e[${i}f\e[${IMAGE[$i]}\e[0m"
  	done >> $IMAGE_FILE
  	# set cursor under the image
  	printf "\e[$(tput lines);1f" >> $IMAGE_FILE
  }
  
  function at_exit() {
  	printf "\e[?9l"          # Turn off mouse reading
  	printf "\e[?12l\e[?25h"  # Turn on cursor
  	stty "$_STTY"            # reinitialize terminal settings
  	clear
  	echo "Thank for using ansipaint!"
  	if [ ! -z "$IMAGE_FILE" ] ; then 
  		echo "Your image is saved as '$IMAGE_FILE'."
  		save_image
  	fi
  	exit
  }
  
  # X = $1, Y = $2
  function set_pos() {
   	echo -en  "\e[$2;$1f"
  }
  
  function show_pos() {
  	set_pos 65 1
  	printf "x,y = %3d,%3d" $X $Y
  }
  
  function show_brush() {
  	set_pos 70 2 
  	printf "[ \e[${FG_COLOR};${BG_COLOR}m$BRUSH\e[0m ]"
  }
  
  function process_click() {
  #	X=$1 Y=$2
  	# set foreground color
  	if [ $Y -eq 1 ] || [ $Y -eq 2 ] ; then
  		if [ $X -gt 2 ] && [ $X -lt 28 ] ; then
  			FG_COLOR="$[Y-1];${FG[$[(X-4)/3]]}"
  			ERASE=0
  		fi
  	fi
  	
  	# set background color
  	if [ $Y -eq 1 ] && [ $X -gt 34 ] ; then
  		if [ $X -gt 34 ] && [ $X -lt 59 ] ; then
  			BG_COLOR="${BG[$[X-35]/3]}"
  			ERASE=0
  		else
  			BG_COLOR="49"
  			ERASE=0
  		fi
  	fi	
  
  	# set brush
  	if [ $Y -eq 2 ] && [ $X -gt 36 ] && [ $X -le 51 ] ; then
  		BRUSH=${BRUSHES[$[(X-37)/2]]}
  		ERASE=0
  	fi
  
  	# set erase
  	if [ $Y -eq 2 ] && [ $X -ge 54 ] && [ $X -le 62 ] ; then
  		BRUSH=" "
  		BG_COLOR="49"
  		ERASE=1
  	fi
  
  	# DEBUG
  	# set_pos 0 25
  	# printf "$FG_COLOR $BG_COLOR $BRUSH"
  }
  
  function draw_menu() {
  	set_pos 1 1; echo "FG: "
  	for i in ${FG[*]}
  	do
  		set_pos $[(i-30)*3+4] 1
  		echo -en "\e[${i}m\e[0m"	
  		set_pos $[(i-30)*3+4] 2
  		echo -en "\e[1;${i}m\e[0m"	
  	done
  
  	set_pos 30 1; echo "BG: "
  	for i in ${BG[*]}
  	do 
  		set_pos $[(i-40)*3+35] 1
  		echo -en "\e[${i}m   \e[0m"	
  	done
  	echo "   |" # default background (49)
  
  	set_pos 30 2; echo -en "Brush: ${BRUSHES[*]}"
  	printf "  [ Erase ]"
  	show_brush
  }
  
  function load_image() {
  	if [ -f $IMAGE_FILE ] ; then 
  		data=$(sed -e 's/\x1b/E/g;s/E\[0m/\n/g;s/E\[2J//' $IMAGE_FILE | \
  			sed -n -e 's/E\[\(.*\)fE\[\(.*m.\)/IMAGE["\1"]="\2"/ p')
  		eval $data
  		cat < $IMAGE_FILE
  	fi
  }
  
  ##########
  #  MAIN  #
  ##########
  trap at_exit ERR EXIT 
  load_image
  draw_menu
  while :
  do 
  	read -N 6 click
  	mouse=( `echo -en ${click#???} | hexdump -v  -e'1/1 " %u"'` )
  	X=$[ ${mouse[0]} - 32]	Y=$[ ${mouse[1]} - 32]
  	process_click
  	show_pos 
  	show_brush
  	if [ $Y -gt 2 ] ; then	
  		echo -en  "\e[${Y};${X}f\e[${FG_COLOR};${BG_COLOR}m$BRUSH\e[0m"
  		if [ $ERASE -eq 0 ] ; then
  			IMAGE["${Y};${X}"]="${FG_COLOR};${BG_COLOR}m$BRUSH"
  		else
  			unset IMAGE["${Y};${X}"]
  		fi
  	fi
  done
  

[1] https://www.youtube.com/watch?v=aoAMxMukgPY