always convert images to NRGBA

this type is rpc-serializable, and we avoid repeated color conversion

io.go

@@ -31,3 +31,14 @@ func writeImage(path string, img image.Image) {
 		log.Fatal(err)
 	}
 }
+
+func imgToNRGBA(img image.Image) *image.NRGBA {
+	b := img.Bounds()
+	r := image.NewNRGBA(b)
+	for x := b.Min.X; x < b.Max.X; x++ {
+		for y := b.Min.Y; y < b.Max.Y; y++ {
+			r.Set(x, y, img.At(x, y))
+		}
+	}
+	return r
+}

main.go

@@ -50,7 +50,7 @@ func main() {
 
 	if *imgPath != "" {
 		offset := image.Pt(*x, *y)
-		img := readImage(*imgPath)
+		img := imgToNRGBA(readImage(*imgPath))
 
 		// check connectivity by opening one test connection
 		conn, err := net.Dial("tcp", *address)

pixelflut/api.go

@@ -14,7 +14,7 @@ import (
 //   using `conns` connections. Pixels are sent column wise, unless `shuffle`
 //   is set. Stops when stop is closed.
 // @cleanup: use FlutTask{} as arg
-func Flut(img image.Image, position image.Point, shuffle bool, address string, conns int, stop chan bool, wg *sync.WaitGroup) {
+func Flut(img *image.NRGBA, position image.Point, shuffle bool, address string, conns int, stop chan bool, wg *sync.WaitGroup) {
 	cmds := commandsFromImage(img, position)
 	if shuffle {
 		cmds.Shuffle()

pixelflut/commands.go

@@ -33,16 +33,14 @@ func (c commands) Shuffle() {
 }
 
 // CommandsFromImage converts an image to the respective pixelflut commands
-func commandsFromImage(img image.Image, offset image.Point) (cmds commands) {
+func commandsFromImage(img *image.NRGBA, offset image.Point) (cmds commands) {
 	b := img.Bounds()
 	cmds = make([][]byte, b.Size().X*b.Size().Y)
 	numCmds := 0
 
 	for x := b.Min.X; x < b.Max.X; x++ {
 		for y := b.Min.Y; y < b.Max.Y; y++ {
-			// ensure we're working with RGBA colors (non-alpha-pre-multiplied)
-			c := color.NRGBAModel.Convert(img.At(x, y)).(color.NRGBA)
-
+			c := img.At(x, y).(color.NRGBA)
 			// ignore transparent pixels
 			if c.A == 0 {
 				continue

rpc/dottir.go

@@ -32,7 +32,7 @@ type Hevring struct {
 type FlutTask struct {
 	Address  string
 	MaxConns int
-	Img      *image.NRGBA // bug :imageType: should be image.Image, but can't be serialized. do conversion in task creation?
+	Img      *image.NRGBA
 	Offset   image.Point
 	Shuffle  bool
 }

rpc/ran.go

@@ -115,13 +115,12 @@ func SummonRán(address string, stopChan chan bool, wg *sync.WaitGroup) *Rán {
 }
 
 // SetTask assigns a FlutTask to Rán, distributing it to all clients
-func (r *Rán) SetTask(img image.Image, offset image.Point, address string, maxConns int) {
+func (r *Rán) SetTask(img *image.NRGBA, offset image.Point, address string, maxConns int) {
 	// @incomplete: smart task creation:
 	//   fetch server state & sample foreign activity in image regions. assign
 	//   subregions to clients (per connection), considering their bandwidth.
 
-	// @bug :imageType
-	r.task = FlutTask{address, maxConns, img.(*image.NRGBA), offset, true}
+	r.task = FlutTask{address, maxConns, img, offset, true}
 	for _, c := range r.clients {
 		ack := FlutAck{}
 		// @speed: should send tasks async