[kaminkatze]

Originally Posted by geekmaster

"Normal" shell arrays did not work for me, but substrings work.

echo ${v:1:1} returns -sh: syntax error: Bad substitution on my K3, and expr substr $v 1 1 is even slower than hexdump.

Here is a ev[ia]l array style version.
eval "v=\$A${x}x$y".

I used 4 values. 0/1 for dead 100/101 for living. 1 and 101 are the dirty states wich are rendered with filled circles.

Spoiler:

#!/bin/sh

#=================================
# initvar - initialize global vars
#---------------------------------
initvar() {
  W=15 H=20; MX=$((W-1)) MY=$((H-1)); G=19 R=5
  LL=300; DLL=$((2*LL))
  for y in $(seq 0 $MY); do for x in $(seq 0 $MX); do
    eval "N${x}x$y=0"
  done; done
  DZ=/dev/zero DN=/dev/null DF=/dev/fb0
  B=$(echo -ne '\xff'); B=$B$B$B$B$B$B$B$B$B$B
  B=$B$B$B$B$B$B$B$B$B$B; B=$B$B$B$B$B$B$B$B$B$B
  eips -c
}

#============================
# load - load common patterns
# usage: load name
#----------------------------
load() {
  case $1 in
    glider) N1x0=101 N2x1=101 N0x2=101 N1x2=101 N2x2=101 ;;
    fill) for y in $(seq 0 $MY); do for x in $(seq 0 $MX); do
            eval "N${x}x$y=101"
          done; done;;
    spaceship) N1x0=101 N2x0=101 N3x0=101 N4x0=101 N4x1=101
               N4x2=101 N3x3=101 N0x1=101 N0x3=101 ;;
  esac
}

#==========================================
# circle - filled midpoint circle algorithm
# usage: echo $B | circle cx cy r
#        circle cx cy r <$DZ
#------------------------------------------
circle() {
  local cx=$1 cy=$2 r=$3; local e=$((-r)) x=$r y=0
  local x0 x1 x2 y0 y1 y2
  while [[ $x -ge $y ]]; do
    x0=$(((cy-x)*DLL+cx)) x1=$(((cy+x)*DLL+cx)) x2=$((2*x))
    y0=$(((cy-y)*DLL+cx)) y1=$(((cy+y)*DLL+cx)) y2=$((2*y))
    dd of=$DF bs=1 count=$x2 seek=$((y1-x))
    dd of=$DF bs=1 count=$x2 seek=$((y1+LL-x))
    dd of=$DF bs=1 count=$x2 seek=$((y0-x))
    dd of=$DF bs=1 count=$x2 seek=$((y0+LL-x))
    dd of=$DF bs=1 count=$y2 seek=$((x1-y))
    dd of=$DF bs=1 count=$y2 seek=$((x1+LL-y))
    dd of=$DF bs=1 count=$y2 seek=$((x0-y))
    dd of=$DF bs=1 count=$y2 seek=$((x0+LL-y))
    e=$((e+2*y+1)); y=$((y+1))
    if [[ $e -ge 0 ]]; then e=$((e-2*x-1)); x=$((x-1)); fi
  done 2>$DN
}

#======================
# update - update field
#----------------------
update() {
  for y in $(seq 0 $MY); do for x in $(seq 0 $MX); do
    eval "c=\$((\$L$(((x+MX)%W))x$(((y+MY)%H))\
               +\$L${x}x$(((y+MY)%H))\
               +\$L$(((x+1)%W))x$(((y+MY)%H))\
               +\$L$(((x+MX)%W))x$y\
               +\$L$(((x+1)%W))x$y\
               +\$L$(((x+MX)%W))x$(((y+1)%H))\
               +\$L${x}x$(((y+1)%H))\
               +\$L$(((x+1)%W))x$(((y+1)%H))))
          v=\$L${x}x$y
          if [[ \$v -lt 2 ]]; then
            [[ \$c -gt 299 -a \$c -lt 400 ]] && v=101 || v=0
          else
            [[ \$c -lt 200 -o \$c -gt 399 ]] && v=1 || v=100
          fi
          N${x}x$y=\$v"
  done; done
}

#=====================================
# render - copy current state and draw
#-------------------------------------
render() {
  for y in $(seq 0 $MY); do for x in $(seq 0 $MX); do
    eval "v=\$N${x}x$y; L${x}x$y=\$v"
    case $v in
      101) echo $B | circle $((x*G+G)) $((y*G+G)) $R ;;
      1) circle $((x*G+G)) $((y*G+G)) $R <$DZ ;;
    esac
  done; done; eips ''
}

#==========================
# loop - render update loop
#--------------------------
loop() { while true; do render; update; done; }

initvar
load glider
loop