gen-twitch-icons.sh

#!/bin/sh
# Generate icons for twitch rewards using imagemagick's or graphicsmagick's convert.
# Quantify the image file if it does not fit in 25kb limits.

if [ -z "$1" ]
then
    echo "Usage: $0 path-to-image-file"
    exit 1
fi

command_exists()
{
    command -v "$1" >/dev/null 2>&1
}

if command_exists convert
then
    convertcom=convert
elif command_exists gm
then
    convertcom="gm convert"
fi

infile="$1"
name="${infile%.*}"

for size in 112x112 56x56 28x28
do
    outfile="$name-$size.png"
    "$convertcom" -resize $size "$infile" "$outfile"
    filesize=$(stat --printf="%s" "$outfile")

    if [ "$filesize" -gt 25600 ]
    then
        if command_exists pngquant
        then
            echo "resulting image $outfile is too large. Using pngquant"
            pngquant -f "$outfile"
        else
            "$convertcom" -resize $size "$infile" -colors 256 "$outfile"
        fi
    fi
done