wowify.sh

#!/bin/bash

# Generate a `:something-wow:` Slack emoji
# With thanks to https://gist.github.com/briancain/2efe69b8870be01bafde829d3933b2d3

set -euo pipefail

if [ $# -eq 0 ]; then
  echo "Usage: $0 input.png"
  exit 1
fi

input=$1
cd "$(dirname "$input")"

fullsize=96
filename=$(basename -- "$input")

basefile="${filename%.*}-base.png"
convert \
  -gravity center \
  -background none \
  -geometry "${fullsize}x${fullsize}" \
  "$filename" \
  "$basefile"
  
sizefile="${filename%.*}-size"
for i in 100 95 90 85 80 75; do
  scaledsize=$((fullsize * 100 / i))
  scaledfile="${sizefile}-${i}.png"

  convert \
    -gravity center \
    -background none \
    -extent "${scaledsize}x${scaledsize}" \
    -geometry "${fullsize}x${fullsize}" \
    "$basefile" \
    "$scaledfile"
done

frame="${filename%.*}-frame"
n=0
for i in 100 95 90 85 80 75 80 85 90 95 100 95 90 85 80 75; do
  cp "${sizefile}-${i}.png" "${frame}-$(printf %03d $n).gif"
  n=$((n + 1))
done

for angle in 45 90 135 180 225 270 315; do
  convert \
    -gravity center \
    -distort ScaleRotateTranslate $angle \
    "${sizefile}-75.png" \
    "${frame}-$(printf %03d $n).gif"
    
  n=$((n + 1))
done

for i in 75 80 85 90 95; do
  cp "${sizefile}-${i}.png" "${frame}-$(printf %03d $n).gif"
  n=$((n + 1))
done

# Combine the frames into a GIF
gif="${filename%.*}-wow.gif"
convert -background none -dispose Background -delay 1x100 -loop 0 "${frame}"-*.gif "$gif"

# Clean up
rm "${basefile}" "${sizefile}"-*.png "${frame}"-*.gif