work on dc6 decoder

formats/dc6/dc6.go

@@ -1,6 +1,7 @@
 package dc6
 
 import (
+	"bytes"
 	"encoding/binary"
 	"io"
 )
@@ -28,7 +29,7 @@ type FrameHeader struct {
 	OffsetY   uint32
 	AllocSize uint32
 	NextBlock uint32
-	Block     uint32
+	Length    uint32
 }
 
 type Frame struct {
@@ -71,20 +72,18 @@ func New(reader io.ReadSeeker) (*Dc6, error) {
 			return nil, err
 		}
 
+		buff := bytes.NewBuffer(make([]byte, frameHeader.Width*frameHeader.Height))
+		// if err := extractFrame(reader, buff, frameHeader); err != nil {
+		if err := extractFrame(reader, nil, frameHeader); err != nil {
+			return nil, err
+		}
+
 		frame := Frame{
 			int(frameHeader.Width),
 			int(frameHeader.Height),
 			int(frameHeader.OffsetX),
 			int(frameHeader.OffsetY),
-			make([]byte, frameHeader.Width*frameHeader.Height),
-		}
-
-		if _, err := io.ReadFull(reader, frame.Data); err != nil {
-			return nil, err
-		}
-
-		if err := extractFrame(reader, frameHeader); err != nil {
-			return nil, err
+			buff.Bytes(),
 		}
 
 		sprite.Frames = append(sprite.Frames, frame)
@@ -93,6 +92,36 @@ func New(reader io.ReadSeeker) (*Dc6, error) {
 	return sprite, nil
 }
 
-func extractFrame(reader io.ReadSeeker, header FrameHeader) error {
+func extractFrame(reader io.ReadSeeker, writer io.WriteSeeker, header FrameHeader) error {
+	var (
+		x uint32
+		y = header.Height - 1
+	)
+
+	var offset uint32
+	for offset < header.Length {
+		var chunkSize byte
+		if err := binary.Read(reader, binary.LittleEndian, &chunkSize); err != nil {
+			return err
+		}
+
+		if chunkSize == 0x80 {
+			x = 0
+			y--
+		} else if (chunkSize & 0x80) != 0 {
+			x += uint32(chunkSize & 0x7f)
+		} else {
+			if _, err := writer.Seek(int64(header.Width*y+x), io.SeekStart); err != nil {
+				return err
+			}
+			if _, err := io.CopyN(writer, reader, int64(chunkSize)); err != nil {
+				return err
+			}
+
+			offset += uint32(chunkSize)
+			x += uint32(chunkSize)
+		}
+	}
+
 	return nil
 }