init

life.sh

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+#!/bin/bash
+#
+# ---------------------------------------------------------
+#
+# script for Conway's Game of Life using ffmpeg filters
+#
+# usage: life.sh <input_image> <num_frames> <fps> <scale>
+# 
+# example: life.sh gosper.png 200 12 10
+# would produce a 200 frame video of life from gosper.png 
+# at 12 fps and 10x resolution of the original image.
+#
+# ---------------------------------------------------------
+#
+# nullprop - 2022
+
+
+set -e
+
+if [ "$#" -ne 4 ]; then
+    echo "invalid number of parameters"
+    echo "usage: life.sh <input_image> <num_frames> <fps> <scale>"
+    exit
+fi
+
+INPUT=$1
+FRAMES=$2
+FPS=$3
+SCALE=$4
+
+rm -rf ./out
+mkdir out
+cp $INPUT out/frame-00000.png
+
+# check if pixel (X, Y) is alive
+is_alive () {
+    echo "\
+        eq( r(X,Y), 0)*\
+        eq( g(X,Y), 0)*\
+        eq( b(X,Y), 0)\
+    "
+}
+
+# check if pixel (X, Y) with offset ($1, $2) is alive.
+# if position is outside image bounds, it is considered dead.
+is_alive_off () {
+    echo "\
+        eq( r(X$1,Y$2), 0)*\
+        eq( g(X$1,Y$2), 0)*\
+        eq( b(X$1,Y$2), 0)*\
+        lt(X$1, W)*\
+        gte(X$1, 0)*\
+        lt(Y$2, H)*\
+        gte(Y$2, 0)\
+    "
+}
+
+# check if pixel (X, Y) has $1 neighbours
+has_neighbours () {
+    echo "\
+        eq(\
+            $1,\
+            $(is_alive_off -1 -1) +\
+            $(is_alive_off -1 +0) +\
+            $(is_alive_off -1 +1) +\
+            $(is_alive_off +0 -1) +\
+            $(is_alive_off +0 +1) +\
+            $(is_alive_off +1 -1) +\
+            $(is_alive_off +1 +0) +\
+            $(is_alive_off +1 +1)\
+        )\
+    "
+}
+
+# should the pixel (X, Y) be alive?
+should_live () {
+    echo "\
+        $(is_alive)*$(has_neighbours 2) +\
+        $(is_alive)*$(has_neighbours 3) +\
+        ifnot($(is_alive), $(has_neighbours 3))
+    "
+}
+
+# load image from $1,
+# step the game forward,
+# and save image to $2
+step () {
+    ffmpeg \
+        -i $1 \
+        -vf \
+            geq="\
+                r='if( $(should_live), 0, 255 )':\
+                b='if( $(should_live), 0, 255 )':\
+                g='if( $(should_live), 0, 255 )':\
+                a=255:
+                interpolation=nearest" \
+        $2
+}
+
+# generate frames
+for ((i=0; i<FRAMES; i++))
+do
+    j=$((i+1))
+    printf -v i_str "%05d" $i
+    printf -v j_str "%05d" $j
+    step out/frame-$i_str.png out/frame-$j_str.png
+done
+
+# combine to video
+ffmpeg -framerate $FPS -pattern_type glob -i 'out/frame-*.png' -c:v libx264 -pix_fmt yuv420p -vf scale="'$SCALE*iw:$SCALE*ih:flags=neighbor'" out/life.mp4