Extract png spritesheets from gamemaker "data.win" files

extract.rb

#!/usr/bin/ruby

PNGHEADER = [0x89, 0x50, 0x4E, 0x47, 0x0D, 0x0A, 0x1A, 0x0A]
PNGENDING = [0x49, 0x45, 0x4E, 0x44, 0xAE, 0x42, 0x60, 0x82]
pngHeaders = []

File.open("data.win", "rb") do |file|
	puts "searching for png headers"
	globalIndex = 0
	headerInnerIndex = 0
	file.each_byte do |byte|
		if (byte == PNGHEADER[headerInnerIndex])
			headerInnerIndex += 1
		else
			headerInnerIndex = 0
		end
		if (headerInnerIndex == PNGHEADER.length)
			puts "png header found at index #{globalIndex - PNGHEADER.length + 1}, recording"
			pngHeaders << globalIndex - PNGHEADER.length + 1
			headerInnerIndex = 0
		end
		globalIndex += 1
	end

	puts "connecting headers with endings"
	pngHeaders.each_with_index do |headerIndex, fileNum|
		foundCorrespondingEnding = false
		endingInnerIndex = 0
		globalIndex = headerIndex
		file.seek(globalIndex, IO::SEEK_SET)
		File.open("#{sprintf("%05d", fileNum)}.png", "wb") do |outFile|
			until foundCorrespondingEnding do
				byte = file.readbyte
				outFile.write(byte.chr)
				if (byte == PNGENDING[endingInnerIndex])
					endingInnerIndex += 1
				else
					endingInnerIndex = 0
				end
				if (endingInnerIndex == PNGENDING.length)
					puts "png ending found at index #{globalIndex - PNGENDING.length + 1}, finishing write"
					foundCorrespondingEnding = true
				end
				globalIndex += 1
			end
		end
	end
end