Uses ImageMagick to generate spritesheets with transparency

spriter.sh

#!/bin/bash
# inspired by https://gist.github.com/968653 (https://github.com/jaymzcd)
# uses imagemagick to create spritesheets out of all the PNG images in a folder.
# There will be 2 passes done:
#   - with the default tiling as determined by imagemagick
#   - with the tiling optimization attempt by this script so as to leave no padding
# It seems that IM does not always produce the best optmization in regard to image size
# so compare and use the one that fits best.
# The spritesheets produced will be:
#   - a PNG with transparency (32bits)
#   - a PNG without transparency channel, where the normally transparent parts show (24bit)
#   - same as previous, but jpg format
#   - a PNG containing only the transparency channel, all others (RGB) being empty
	
	#jpg quality
	if [ $1 ]
	then
		qual=$1"%";
	else
		qual="70%";
	fi 

	#name of spritesheet files
	if [ $2 ]
	then
		classname=$2;
	else
		classname="sprite";
	fi

	#the folder in which we put the spritesheets
	dirName="spritesheets";
	mkdir $dirName;

	# the extension to iterate over for input files
	ext=".png"; 

	file=$(ls *$ext | head -1);
	#calculate width of single sprite image
	width=`identify -format "%[fx:w]" "$file"`;
	height=`identify -format "%[fx:h]" "$file"`;

	#number of sprite files
	n=$( ls *$ext -1 | wc -l);
	# attempt to find a rectangle that needs no padding, the largest possible
	# as it seems png compresses better on large images rather than high ones
	# from my tests, but this might need to be investigated further.
	# Anyway, the dimension that IM gives by default is not always the optimal 
	# one with regard to filesize
	pad=$n;
	nx=$(echo "$n / 2 + 1" | bc);
	while [ $nx -gt 1 -a $pad -gt 0 ]; do
		let nx=nx-1;
		curPad=$(echo "$n % $nx" | bc);
		if [ $curPad -lt $pad ]
		then
			pad=$curPad;
		fi   
	done

	tilingPasses=("0" $nx"x");
	
	FILES=$(ls *$ext | sort -n | tr '\n' ' ');

	for i in $(seq 0 $((${#tilingPasses[*]} - 1))); do
		tiling=${tilingPasses[$i]};
		subDirName="tiling-"$tiling;
		mkdir $dirName/$subDirName;

		echo "Generating 32 bits sprite (with alpha) tile "$tiling;
		montage -alpha Set -background none -tile $tiling -geometry +0+0 \
		${FILES[@]} PNG32:$dirName/$subDirName/$classname"-complete.png";

		echo "Generating 24 bits sprite (without alpha, png) tile "$tiling;
		montage -alpha Deactivate -tile $tiling -geometry +0+0 \
		${FILES[@]} PNG32:$dirName/$subDirName/$classname".png";

		echo "Generating 24 bits sprite (without alpha, jpg) tile "$tiling;
		montage -alpha Deactivate -tile $tiling -geometry +0+0 -quality $qual \
		${FILES[@]} $dirName/$subDirName/$classname".jpg";

		echo "Generating 32 bits sprite of alpha only, tile "$tiling;
		convert <(montage -background none -alpha Set -tile $tiling -geometry +0+0 ${FILES[@]} miff:-) \
		-alpha off -fill black -colorize 100% -alpha on \
		PNG32:$dirName/$subDirName/$classname"-alpha.png";
	done;