write frames to png files and some clean up

datatypes.go

@@ -69,6 +69,10 @@ type ImageDescriptor struct {
 	Packed byte   // image and color table data information
 }
 
+/********************/
+/* EXTENSION BLOCKS */
+/********************/
+
 /*
 GraphicsControlPacked {
 	0:   TransparentColorFlag
@@ -78,10 +82,6 @@ GraphicsControlPacked {
 }
 */
 
-/********************/
-/* EXTENSION BLOCKS */
-/********************/
-
 // Only available on 89a and comes after the global color table and before the 1st image
 type GraphicsControlBlock struct {
 	Packed                byte  // method of graphics disposal to use

main.go

@@ -31,6 +31,18 @@ func (v Palette) UnmarshalBinary(data []byte) error {
 	return nil
 }
 
+func (v Palette) MarshalBinary() []byte {
+	data := make([]byte, len(v)*3)
+
+	for i := 0; i < len(v); i++ {
+		data[i*3] = v[i].Red
+		data[i*3+1] = v[i].Green
+		data[i*3+2] = v[i].Blue
+	}
+
+	return data
+}
+
 func deinterlace() {
 	// TODO:
 }
@@ -59,7 +71,7 @@ func main() {
 		fmt.Print("WARNING: some features are unimplemented for this version. Some images may not extract correctly\n\n")
 	}
 	fmt.Printf("GIF aspect ratio is: %v\n", header.AspectRatio)
-	fmt.Printf("GIF background color is: %v\n", header.BackgroundColor)
+	fmt.Printf("GIF background color index is: %v\n", header.BackgroundColor)
 	fmt.Printf("GIF height is: %v\n", header.ScreenHeight)
 	fmt.Printf("GIF width is: %v\n", header.ScreenWidth)
 
@@ -78,20 +90,20 @@ func main() {
 	}
 	dirName := strings.Split(st.Name(), ".gif")[0]
 
-	fmt.Printf("%v\n", dirName)
 	os.Mkdir(dirName, os.FileMode(0755))
 
-	var palette Palette
+	var globalPalette Palette
+	var currentPalette Palette
+	transparencyIndex := -1
 
-	if GlobalColorTableFlag == 0 { // no global color table, use default one (???)
+	if GlobalColorTableFlag == 1 { // global color table exists, use it
-		// TODO: do we skip it. no idea if this is accurate
-		file.Seek(int64(GlobalColorTableSize), os.SEEK_CUR)
-	} else { // global color table exists, use it
 		globalColorTable := make([]byte, GlobalColorTableSize)
 		file.Read(globalColorTable)
 
-		palette = make(Palette, GlobalColorTableEntries)
+		globalPalette = make(Palette, GlobalColorTableEntries)
-		palette.UnmarshalBinary(globalColorTable)
+		globalPalette.UnmarshalBinary(globalColorTable)
+
+		currentPalette = globalPalette
 	}
 
 	counter := 1
@@ -100,16 +112,12 @@ func main() {
 		nextByte := make([]byte, 1)
 		file.Read(nextByte)
 
-		// fmt.Printf("next byte is: 0x%x\n", nextByte[0])
-
 		switch nextByte[0] {
 		case EXTENSION_BLOCK:
 			{
 				nextSecondByte := make([]byte, 1)
 				file.Read(nextSecondByte)
 
-				// fmt.Printf("next second byte is: 0x%x\n", nextSecondByte[0])
-
 				switch nextSecondByte[0] {
 				case PLAINTEXT_BLOCK:
 					{
@@ -124,9 +132,23 @@ func main() {
 					}
 				case GRAPHICS_CONTROL_BLOCK:
 					{
-						file.Seek(GRAPHICS_CONTROL_BLOCK_SIZE+1, os.SEEK_CUR)
+						// skip the length byte
+						file.Seek(1, os.SEEK_CUR)
 
-						// TODO: read graphics control block and do something with it ???
+						// TODO: use the delayTime for something ???
+
+						block := GraphicsControlBlock{}
+						data := make([]byte, GRAPHICS_CONTROL_BLOCK_SIZE)
+
+						file.Read(data)
+
+						binary.Read(bytes.NewBuffer(data), binary.LittleEndian, &block)
+
+						transparencyFlag := block.Packed & 1
+
+						if transparencyFlag == 1 {
+							transparencyIndex = int(block.TransparentColorIndex)
+						}
 
 						break
 					}
@@ -168,27 +190,18 @@ func main() {
 				SortFlag := (imageDescriptor.Packed & 0x20) >> 5
 				LocalColorTableEntries := math.Pow(2, float64((imageDescriptor.Packed&7)+1))
 
-				// fmt.Printf("Local Color Table Flag: %v\n", LocalColorTableFlag)
+				// TODO: use offsets when writing image ??
-				// fmt.Printf("Interlace Flag: %v\n", InterlaceFlag)
-				// fmt.Printf("Sort Flag: %v\n", SortFlag)
-				// fmt.Printf("Local Color Table Entries: %v\n", LocalColorTableEntries)
-
-				fmt.Printf("Left Offset: %v\n", imageDescriptor.Left)
-				fmt.Printf("Top Offset: %v\n", imageDescriptor.Top)
-
-				// TODO: use color tables for correct colors on pixels
-				// TODO: write the image data to PNG
 
 				// local color table comes first
-				var LocalColorTable Palette
+				var localPalette Palette
 				if LocalColorTableFlag == 1 {
 					tempLocalColorTable := make([]byte, int(LocalColorTableEntries*3))
 					file.Read(tempLocalColorTable)
 
-					LocalColorTable = make(Palette, int(LocalColorTableEntries))
+					localPalette = make(Palette, int(LocalColorTableEntries))
-					LocalColorTable.UnmarshalBinary(tempLocalColorTable)
+					localPalette.UnmarshalBinary(tempLocalColorTable)
 
-					// TODO: use local color table
+					currentPalette = localPalette
 				}
 
 				if InterlaceFlag == 1 {
@@ -213,17 +226,14 @@ func main() {
 					panic(err)
 				}
 
-				outFile, err := os.OpenFile(fmt.Sprintf("./%s/%s-raw.%v", dirName, st.Name(), counter), os.O_CREATE|os.O_RDWR, os.FileMode(0755))
+				fileName := fmt.Sprintf("./%s/%s-%v.png", dirName, dirName, counter)
-				if err != nil {
+				WriteToPNG(decompressedFrameData, currentPalette, fileName, imageDescriptor.Width, imageDescriptor.Height, transparencyIndex)
-					panic(err)
-				}
-
-				outFile.Write(decompressedFrameData)
 
 				counter++
 				break
 			}
 		}
+		currentPalette = globalPalette
 
 		// skip the terminator byte
 		file.Seek(1, os.SEEK_CUR)

png.go

@@ -0,0 +1,194 @@
+package main
+
+import (
+	"bytes"
+	"compress/zlib"
+	"encoding/binary"
+	"hash/crc32"
+	"io/fs"
+	"os"
+)
+
+func writeHeader(pngFile *os.File) {
+	header := []byte{0x89, 0x50, 0x4e, 0x47, 0x0d, 0x0a, 0x1a, 0x0a}
+	_, err := pngFile.Write(header)
+	if err != nil {
+		panic(err)
+	}
+}
+
+func writeIHDR(pngFile *os.File, width uint16, height uint16) {
+	chunkLength := []byte{0x00, 0x00, 0x00, 0x0D} // always 13
+	IHDR := []byte{0x49, 0x48, 0x44, 0x52}        // IHDR string
+	bitDepth := byte(0x8)                         // number of bits per sample or per palette index (always 8 for indexed-color)
+	colorType := byte(0x3)                        // 3 is Indexed-color which is what's used for GIFs. this also means a PLTE chunk needs to exist
+	compressionMethod := byte(0x0)                // always 0
+	filterMethod := byte(0x0)                     // always 0
+	interlaceMethod := byte(0x0)                  // 0 or 1
+	hash := make([]byte, 4)                       // crc-32 hash of the previous 13 bytes
+
+	chunkData := make([]byte, 13)
+
+	binary.BigEndian.PutUint32(chunkData[0:4], uint32(width))
+	binary.BigEndian.PutUint32(chunkData[4:8], uint32(height))
+	chunkData[8] = bitDepth
+	chunkData[9] = colorType
+	chunkData[10] = compressionMethod
+	chunkData[11] = filterMethod
+	chunkData[12] = interlaceMethod
+
+	binary.BigEndian.PutUint32(hash, crc32.Update(crc32.ChecksumIEEE(IHDR), crc32.IEEETable, chunkData))
+
+	_, err := pngFile.Write(chunkLength)
+	if err != nil {
+		panic(err)
+	}
+	_, err = pngFile.Write(IHDR)
+	if err != nil {
+		panic(err)
+	}
+	_, err = pngFile.Write(chunkData)
+	if err != nil {
+		panic(err)
+	}
+	_, err = pngFile.Write(hash)
+	if err != nil {
+		panic(err)
+	}
+}
+
+func writePLTE(pngFile *os.File, palette Palette) {
+	chunkLength := make([]byte, 4)
+	PLTE := []byte{0x50, 0x4C, 0x54, 0x45}
+	hash := make([]byte, 4)
+
+	binary.BigEndian.PutUint32(chunkLength, uint32(len(palette)*3))
+	binary.BigEndian.PutUint32(hash, crc32.Update(crc32.ChecksumIEEE(PLTE), crc32.IEEETable, palette.MarshalBinary()))
+
+	_, err := pngFile.Write(chunkLength)
+	if err != nil {
+		panic(err)
+	}
+	_, err = pngFile.Write(PLTE)
+	if err != nil {
+		panic(err)
+	}
+	_, err = pngFile.Write(palette.MarshalBinary())
+	if err != nil {
+		panic(err)
+	}
+	_, err = pngFile.Write(hash)
+	if err != nil {
+		panic(err)
+	}
+}
+
+func writetRNS(pngFile *os.File, transparencyIndex int) {
+	chunkLength := make([]byte, 4)
+	tRNS := []byte{0x74, 0x52, 0x4E, 0x53}
+	hash := make([]byte, 4)
+
+	binary.BigEndian.PutUint32(chunkLength, uint32(transparencyIndex)+1)
+
+	data := make([]byte, transparencyIndex+1)
+	for i := 0; i < transparencyIndex; i++ {
+		data[i] = 0xFF
+	}
+
+	data[transparencyIndex] = 0
+
+	binary.BigEndian.PutUint32(hash, crc32.Update(crc32.ChecksumIEEE(tRNS), crc32.IEEETable, data))
+
+	_, err := pngFile.Write(chunkLength)
+	if err != nil {
+		panic(err)
+	}
+	_, err = pngFile.Write(tRNS)
+	if err != nil {
+		panic(err)
+	}
+	_, err = pngFile.Write(data)
+	if err != nil {
+		panic(err)
+	}
+	_, err = pngFile.Write(hash)
+	if err != nil {
+		panic(err)
+	}
+}
+
+func serialize(data []byte, width int, height int) []byte {
+	b := make([]byte, 0, (width+1)*height)
+	for i := 0; i < height; i++ {
+		b = append(b, 0)
+		b = append(b, data[width*i:width*(i+1)]...)
+	}
+	return b
+}
+
+func writeIDAT(pngFile *os.File, data []byte, width uint16, height uint16) {
+	chunkLength := make([]byte, 4)
+	IDAT := []byte{0x49, 0x44, 0x41, 0x54}
+	hash := make([]byte, 4)
+
+	binary.BigEndian.PutUint32(chunkLength, uint32(len(data)))
+	binary.BigEndian.PutUint32(hash, crc32.Update(crc32.ChecksumIEEE(IDAT), crc32.IEEETable, data))
+
+	_, err := pngFile.Write(chunkLength)
+	if err != nil {
+		panic(err)
+	}
+	_, err = pngFile.Write(IDAT)
+	if err != nil {
+		panic(err)
+	}
+	var buf bytes.Buffer
+	writer, err := zlib.NewWriterLevel(&buf, zlib.BestCompression)
+	if err != nil {
+		panic(err)
+	}
+	defer writer.Close()
+	_, err = writer.Write(serialize(data, int(width), int(height)))
+	if err != nil {
+		panic(err)
+	}
+	writer.Flush()
+	_, err = pngFile.Write(buf.Bytes())
+	if err != nil {
+		panic(err)
+	}
+	_, err = pngFile.Write(hash)
+	if err != nil {
+		panic(err)
+	}
+}
+
+func writeIEND(pngFile *os.File) {
+	chunkLength := []byte{0x00, 0x00, 0x00, 0x00}
+	IEND := []byte{0x49, 0x45, 0x4E, 0x44}
+	hash := make([]byte, 4)
+	binary.BigEndian.PutUint32(hash, crc32.Update(crc32.ChecksumIEEE(IEND), crc32.IEEETable, nil))
+
+	IENDChunk := append(chunkLength, append(IEND, hash...)...)
+	_, err := pngFile.Write(IENDChunk)
+	if err != nil {
+		panic(err)
+	}
+}
+
+func WriteToPNG(data []byte, palette Palette, fileName string, width uint16, height uint16, transparenyIndex int) {
+	pngFile, err := os.OpenFile(fileName, os.O_CREATE|os.O_WRONLY, fs.FileMode(0755))
+	if err != nil {
+		panic(err)
+	}
+
+	writeHeader(pngFile)
+	writeIHDR(pngFile, width, height)
+	writePLTE(pngFile, palette)
+	if transparenyIndex != -1 {
+		writetRNS(pngFile, transparenyIndex)
+	}
+	writeIDAT(pngFile, data, width, height)
+	writeIEND(pngFile)
+	pngFile.Close()
+}