speed up pixel fetching

main.go

@@ -52,18 +52,21 @@ func main() {
 	fetchedImg := image.NewNRGBA(img.Bounds().Add(offset))
 
 	if *fetchImgPath != "" {
-		// using img.SubImage to distribute tasks is nice, as we can also parallelize command generation easily!
-		// @cleanup: use a box tiling algo instead of hardcoding
-		b := fetchedImg.Bounds()
-		b1 := image.Rectangle{b.Min, b.Size().Div(2)}
-		b2 := b1.Add(image.Pt(b1.Dx(), 0))
-		b3 := b1.Add(image.Pt(0, b1.Dy()))
-		b4 := b1.Add(b1.Size())
-		go pixelflut.FetchImage(fetchedImg.SubImage(b1).(*image.NRGBA), *address)
-		go pixelflut.FetchImage(fetchedImg.SubImage(b2).(*image.NRGBA), *address)
-		go pixelflut.FetchImage(fetchedImg.SubImage(b3).(*image.NRGBA), *address)
-		go pixelflut.FetchImage(fetchedImg.SubImage(b4).(*image.NRGBA), *address)
-		*connections -= 4
+		fetchCmds := pixelflut.CmdsFetchImage(fetchedImg.Bounds())
+		fetchMessages := fetchCmds.Chunk(1)
+
+		{
+			// @cleanup: encapsulate this in separate function exported from pixelflut
+			conn, err := net.Dial("tcp", *address)
+			if err != nil {
+				log.Fatal(err)
+			}
+			// defer conn.Close()
+
+			go pixelflut.FetchPixels(fetchedImg, conn)
+			go pixelflut.Bomb2(fetchMessages[0], conn)
+		}
+		*connections -= 1
 	}
 
 	// Generate and split messages into equal chunks

pixelflut/fetch.go

@@ -1,57 +1,19 @@
 package pixelflut
 
 import (
-	"bufio"
-	"encoding/hex"
 	"fmt"
 	"image"
-	"image/color"
-	"log"
-	"net"
-	"net/textproto"
-	"strings"
 )
 
-func FetchImage(img *image.NRGBA, address string) {
-	// FIXME @speed: this is unusably s l o w w w
-	// bottleneck seems to be our pixel reading/parsing code. cpuprofile!
-	// -> should buffer it just as in bomb()
-
-	conn, err := net.Dial("tcp", address)
-	if err != nil {
-		log.Fatal(err)
-	}
-	defer conn.Close()
-
-	reader := bufio.NewReader(conn)
-	tp := textproto.NewReader(reader)
-
-	b := img.Bounds()
-	for {
-		for x := b.Min.X; x < b.Max.X; x++ {
-			for y := b.Min.Y; y < b.Max.Y; y++ {
-				// request pixel
-				fmt.Fprintf(conn, "PX %d %d\n", x, y)
-				if err != nil {
-					log.Fatal(err)
-				}
-
-				// read pixel
-				// @speed try to run this in a separate goroutine?
-				// we probably need to buffer the responses then
-				res, err := tp.ReadLine()
-				if err != nil {
-					log.Fatal(err)
-				}
-				res2 := strings.Split(res, " ")
-				col, _ := hex.DecodeString(res2[3])
-				img.Set(x, y, color.NRGBA{
-					uint8(col[0]),
-					uint8(col[1]),
-					uint8(col[2]),
-					255,
-				})
-			}
+func CmdsFetchImage(bounds image.Rectangle) (cmds Commands) {
+	cmds = make([][]byte, bounds.Size().X*bounds.Size().Y)
+	numCmds := 0
+	for x := bounds.Min.X; x < bounds.Max.X; x++ {
+		for y := bounds.Min.Y; y < bounds.Max.Y; y++ {
+			cmd := fmt.Sprintf("PX %d %d\n", x, y)
+			cmds[numCmds] = []byte(cmd)
+			numCmds++
 		}
 	}
+	return cmds
 }

pixelflut/net.go

@@ -1,10 +1,20 @@
 package pixelflut
 
 import (
-	"net"
+	"bufio"
+	"encoding/hex"
+	"image"
+	"image/color"
 	"log"
+	"net"
+	"net/textproto"
+	"strconv"
+	"strings"
 )
 
+// @speed: add some performance reporting mechanism on these functions when
+//   called as goroutines
+
 // Bomb writes the given message via plain TCP to the given address,
 // forever, as fast as possible.
 func Bomb(message []byte, address string) {
@@ -14,6 +24,11 @@ func Bomb(message []byte, address string) {
 	}
 	defer conn.Close()
 
+	Bomb2(message, conn)
+}
+
+// @cleanup: find common interface instead of Bomb2
+func Bomb2(message []byte, conn net.Conn) {
 	for {
 		_, err := conn.Write(message)
 		if err != nil {
@@ -21,3 +36,31 @@ func Bomb(message []byte, address string) {
 		}
 	}
 }
+
+func FetchPixels(target *image.NRGBA, conn net.Conn) {
+	reader := bufio.NewReader(conn)
+	tp := textproto.NewReader(reader)
+
+	for {
+		// @speed: textproto seems not the fastest, buffer text manually & split at \n ?
+		res, err := tp.ReadLine()
+		if err != nil {
+			log.Fatal(err)
+		}
+
+		// @speed: Split is ridiculously slow due to mallocs!
+		//   chunk last 6 chars off -> color, remove first 3 chars, find space in
+		//   remainder, then Atoi() xy?
+		res2 := strings.Split(res, " ")
+		x, _ := strconv.Atoi(res2[1])
+		y, _ := strconv.Atoi(res2[2])
+		col, _ := hex.DecodeString(res2[3])
+
+		target.Set(x, y, color.NRGBA{
+			uint8(col[0]),
+			uint8(col[1]),
+			uint8(col[2]),
+			255,
+		})
+	}
+}

pixelflut/send.go

@@ -24,7 +24,7 @@ func CommandsFromImage(img image.Image, offset image.Point) (commands Commands)
 			// @incomplete: also send alpha? -> bandwidth tradeoff
 			// @speed: this sprintf call is quite slow..
 			cmd := fmt.Sprintf("PX %d %d %.2x%.2x%.2x\n",
-				x + offset.X, y + offset.Y, c.R, c.G, c.B)
+				x+offset.X, y+offset.Y, c.R, c.G, c.B)
 			commands[numCmds] = []byte(cmd)
 			numCmds++
 		}