new randoffset for each draw

pixelflut/api.go

@@ -6,7 +6,6 @@ import (
 	"image"
 	"image/color"
 	"log"
-	"math/rand"
 	"net"
 	"sync"
 
@@ -37,9 +36,11 @@ func Flut(img *image.NRGBA, position image.Point, shuffle, rgbsplit, randoffset,
 	}
 
 	var messages [][]byte
-	var maxX, maxY int
+	var maxOffsetX, maxOffsetY int
 	if randoffset {
-		maxX, maxY = CanvasSize(address)
+		maxX, maxY := CanvasSize(address)
+		maxOffsetX = maxX - img.Bounds().Canon().Dx()
+		maxOffsetY = maxY - img.Bounds().Canon().Dy()
 		messages = cmds.Chunk(1) // each connection should send the full img
 	} else {
 		messages = cmds.Chunk(conns)
@@ -52,15 +53,7 @@ func Flut(img *image.NRGBA, position image.Point, shuffle, rgbsplit, randoffset,
 			msg = messages[i]
 		}
 
-		bombWg.Add(1)
-		if randoffset {
-			msg = append(OffsetCmd(
-				rand.Intn(maxX-img.Bounds().Canon().Dx()),
-				rand.Intn(maxY-img.Bounds().Canon().Dy()),
-			), msg...)
-		}
-
-		go bombAddress(msg, address, stop, &bombWg)
+		go bombAddress(msg, address, maxOffsetX, maxOffsetY, stop, &bombWg)
 	}
 	bombWg.Wait()
 	if wg != nil {
@@ -98,7 +91,7 @@ func FetchImage(bounds image.Rectangle, address string, conns int, stop chan boo
 		}
 
 		go readPixels(img, conn, stop)
-		go bombConn(cmds[i], conn, stop)
+		go bombConn(cmds[i], 0, 0, conn, stop)
 	}
 
 	return img

pixelflut/commands.go

@@ -32,7 +32,7 @@ func (c commands) Shuffle() {
 	}
 }
 
-// AddOffset uses the OFFSET command to send the image at a specific place (not supported by all servers. example: https://github.com/TobleMiner/shoreline)
+// OffsetCmd applies offset to all following requests. Not supported by all servers. example: https://github.com/TobleMiner/shoreline.
 func OffsetCmd(x, y int) []byte {
 	return []byte(fmt.Sprintf("OFFSET %d %d\n", x, y))
 }

pixelflut/net.go

@@ -3,6 +3,7 @@ package pixelflut
 import (
 	"fmt"
 	"log"
+	"math/rand"
 	"net"
 	"sync"
 	"time"
@@ -74,26 +75,37 @@ func initPerfReporter() *Performance {
 
 // bombAddress writes the given message via plain TCP to the given address,
 // as fast as possible, until stop is closed.
-func bombAddress(message []byte, address string, stop chan bool, wg *sync.WaitGroup) {
+func bombAddress(message []byte, address string, maxOffsetX, maxOffsetY int, stop chan bool, wg *sync.WaitGroup) {
+	wg.Add(1)
+	defer wg.Done()
 	conn, err := net.Dial("tcp", address)
 	if err != nil {
 		log.Fatal(err)
 	}
 	defer conn.Close()
-	bombConn(message, conn, stop)
-	wg.Done()
+	bombConn(message, maxOffsetX, maxOffsetY, conn, stop)
 }
 
-func bombConn(message []byte, conn net.Conn, stop chan bool) {
+func bombConn(message []byte, maxOffsetX, maxOffsetY int, conn net.Conn, stop chan bool) {
 	PerformanceReporter.connsReporter <- 1
 	defer func() { PerformanceReporter.connsReporter <- -1 }()
 
+	var msg = make([]byte, len(message)+16) // leave some space for offset cmd
+	msg = message
+	randOffset := maxOffsetX > 1 && maxOffsetY > 0
+
 	for {
 		select {
 		case <-stop:
 			return
 		default:
-			b, err := conn.Write(message)
+			if randOffset {
+				msg = append(
+					OffsetCmd(rand.Intn(maxOffsetX), rand.Intn(maxOffsetY)),
+					message...,
+				)
+			}
+			b, err := conn.Write(msg)
 			if err != nil {
 				log.Fatal(err)
 			}