Split off the container bits to separate package

container/dmd1.go

@@ -0,0 +1,59 @@
+package container
+
+import (
+	"encoding/binary"
+	"io"
+)
+
+// DMD1Chunk is a named chunk.
+type DMD1Chunk struct {
+	// Name of the chunk.
+	Name [4]byte
+
+	// Size of the chunk, including the name of the chunk.
+	Size uint32
+
+	// Data is the payload of the chunk.
+	Data []byte
+}
+
+func (chunk *DMD1Chunk) ReadFrom(r io.Reader) (n int64, err error) {
+	if err = binary.Read(r, binary.LittleEndian, &chunk.Name); err != nil {
+		return
+	}
+	if err = binary.Read(r, binary.LittleEndian, &chunk.Size); err != nil {
+		return
+	}
+	chunk.Data = make([]byte, chunk.Size)
+	if chunk.Size > 0 {
+		if _, err = io.ReadFull(r, chunk.Data); err != nil {
+			return
+		}
+	}
+	return 8 + int64(chunk.Size), nil
+}
+
+func (chunk *DMD1Chunk) WriteTo(w io.Writer) (n int64, err error) {
+	if err = binary.Write(w, binary.LittleEndian, chunk.Name); err != nil {
+		return
+	}
+	n += 4
+	chunk.Size = uint32(len(chunk.Data))
+	if err = binary.Write(w, binary.LittleEndian, chunk.Size); err != nil {
+		return
+	}
+	n += 4
+	if chunk.Size > 0 {
+		var m int
+		if m, err = w.Write(chunk.Data); err != nil {
+			return
+		}
+		n += int64(m)
+	}
+	return
+}
+
+var (
+	_ io.ReaderFrom = (*DMD1Chunk)(nil)
+	_ io.WriterTo   = (*DMD1Chunk)(nil)
+)

container/doc.go

@@ -0,0 +1,4 @@
+/*
+Package container contains helpers for animation(set) containers.
+*/
+package container

dmd1.go

@@ -10,6 +10,8 @@ import (
 	"path/filepath"
 	"time"
 
+	"maze.io/x/dmd/container"
+
 	"maze.io/x/dmd/bitmap"
 )
 
@@ -25,7 +27,7 @@ const (
 
 // DecodeDMD1 decodes one DMD1 animation (as used in RPI2DMD).
 func DecodeDMD1(r io.Reader) (Animation, error) {
-	var chunk DMD1Chunk
+	var chunk container.DMD1Chunk
 	if _, err := chunk.ReadFrom(r); err != nil {
 		return nil, err
 	} else if name := string(chunk.Name[:]); name != dmd1Magic {
@@ -51,7 +53,7 @@ func DecodeDMD1(r io.Reader) (Animation, error) {
 		// log.Printf("dmd: DMD1 chunk %q of size %d", name, chunk.size)
 		switch name {
 		case dmd1VersionChunk:
-			if chunk.size != 4 {
+			if chunk.Size != 4 {
 				return nil, fmt.Errorf("dmd1: unexpected %q chunk size", name)
 			}
 			var version uint32
@@ -71,7 +73,7 @@ func DecodeDMD1(r io.Reader) (Animation, error) {
 }
 
 func decodeDMD1Animation(r io.Reader, a *imageAnimation) error {
-	var chunk DMD1Chunk
+	var chunk container.DMD1Chunk
 	for {
 		if _, err := chunk.ReadFrom(r); err == io.EOF {
 			return nil
@@ -117,14 +119,14 @@ func decodeDMD1Animation(r io.Reader, a *imageAnimation) error {
 }
 
 func decodeDMD1Frame(r io.Reader, width, height int) (i image.Image, d time.Duration, err error) {
-	var chunk DMD1Chunk
+	var chunk container.DMD1Chunk
 
 	// TIME chunk.
 	if _, err = chunk.ReadFrom(r); err != nil {
 		return
 	} else if name := string(chunk.Name[:]); name != dmd1FrameTimeChunk {
 		return nil, 0, fmt.Errorf("dmd: expected DMD1 %q chunk, got %q", dmd1FrameTimeChunk, name)
-	} else if chunk.size != 4 {
+	} else if chunk.Size != 4 {
 		return nil, 0, fmt.Errorf("dmd: unexpected DMD1 %q chunk size", name)
 	}
 	d = time.Duration(binary.LittleEndian.Uint32(chunk.Data)) * time.Millisecond
@@ -134,8 +136,8 @@ func decodeDMD1Frame(r io.Reader, width, height int) (i image.Image, d time.Dura
 		return
 	} else if name := string(chunk.Name[:]); name != dmd1FrameDataChunk {
 		return nil, 0, fmt.Errorf("dmd: expected DMD1 %q chunk, got %q", dmd1FrameDataChunk, name)
-	} else if need := uint32(width*height*4) / 2; chunk.size < need {
-		return nil, 0, fmt.Errorf("dmd: expected DMD1 %q chunk size of %d, got %d", dmd1FrameDataChunk, need, chunk.size)
+	} else if need := uint32(width*height*4) / 2; chunk.Size < need {
+		return nil, 0, fmt.Errorf("dmd: expected DMD1 %q chunk size of %d, got %d", dmd1FrameDataChunk, need, chunk.Size)
 	}
 
 	img := bitmap.NewRGBA16Image(image.Rect(0, 0, width, height))
@@ -151,102 +153,5 @@ func decodeDMD1Frame(r io.Reader, width, height int) (i image.Image, d time.Dura
 		img.Pix[i] |= 0x0f
 	}
 
-	/*
-		img := image.NewRGBA(image.Rect(0, 0, width, height))
-		for y := 0; y < height; y++ {
-			o := y * width * 2
-			for x := 0; x < width; x, o = x+1, o+2 {
-				c := binary.LittleEndian.Uint16(chunk.Data[o:])
-				r := uint8((c & 0xf000) >> 12)
-				r |= r << 4
-				g := uint8((c & 0x0f00) >> 8)
-				g |= g << 4
-				b := uint8((c & 0x00f0) >> 4)
-				b |= b << 4
-				img.Set(x, y, color.RGBA{R: r, G: g, B: b, A: 0xff})
-			}
-		}
-
-	*/
-	/*
-		for y := 0; y < height; y++ {
-			o := y * width
-			for x := 0; x < width; x, o = x+1, o+1 {
-				// Pixel data is stored in nibbles, so the nth pixel starts at the n*3rd nibble.
-				//   01 23 45 67 89 ..
-				//   RG BR GB RG BR GB
-				n := o * 3 // nibble
-				if n&1 == 0 {
-					// Starts at byte.
-					n /= 2
-					r := chunk.Data[n] >> 4
-					r |= r << 4
-					g := chunk.Data[n] & 0xf
-					g |= g << 4
-					b := chunk.Data[n+1] >> 4
-					b |= b << 4
-					img.Set(x, y, color.RGBA{R: r, G: g, B: b, A: 0xff})
-				} else {
-					// Starts at nibble.
-					n /= 2
-					r := chunk.Data[n] & 0xf
-					r |= r << 4
-					g := chunk.Data[n+1] >> 4
-					g |= g << 4
-					b := chunk.Data[n+1] & 0xf
-					b |= b << 4
-					img.Set(x, y, color.RGBA{R: r, G: g, B: b, A: 0xff})
-				}
-			}
-		}
-	*/
-
 	return img, d, nil
 }
-
-type DMD1Chunk struct {
-	Name [4]byte
-	size uint32
-	Data []byte
-}
-
-func (chunk *DMD1Chunk) ReadFrom(r io.Reader) (n int64, err error) {
-	if err = binary.Read(r, binary.LittleEndian, &chunk.Name); err != nil {
-		return
-	}
-	if err = binary.Read(r, binary.LittleEndian, &chunk.size); err != nil {
-		return
-	}
-	chunk.Data = make([]byte, chunk.size)
-	if chunk.size > 0 {
-		if _, err = io.ReadFull(r, chunk.Data); err != nil {
-			return
-		}
-	}
-	return 8 + int64(chunk.size), nil
-}
-
-func (chunk *DMD1Chunk) WriteTo(w io.Writer) (n int64, err error) {
-	if err = binary.Write(w, binary.LittleEndian, chunk.Name); err != nil {
-		return
-	}
-	n += 4
-	chunk.size = uint32(len(chunk.Data))
-	if err = binary.Write(w, binary.LittleEndian, chunk.size); err != nil {
-		return
-	}
-	n += 4
-	if chunk.size > 0 {
-		var m int
-		if m, err = w.Write(chunk.Data); err != nil {
-			return
-		}
-		n += int64(m)
-	}
-	return
-}
-
-var (
-	_ io.ReaderFrom = (*DMD1Chunk)(nil)
-	_ io.WriterTo   = (*DMD1Chunk)(nil)
-)