add -hevring-preview flag

enables storing of the current task image to a local file

main.go

@@ -20,13 +20,14 @@ import (
 var (
 	imgPath        = flag.String("image", "", "Filepath of an image to flut")
 	ránAddr        = flag.String("rán", "", "Start RPC server to distribute jobs, listening on the given address/port")
-	hevringAddr  = flag.String("hevring", "", "Connect to PRC server at given address/port")
+	hevringAddr    = flag.String("hevring", "", "Connect to RPC server at given address/port")
 	address        = flag.String("host", ":1234", "Target server address")
 	connections    = flag.Int("connections", 4, "Number of simultaneous connections. Each connection posts a subimage")
 	x              = flag.Int("x", 0, "Offset of posted image from left border")
 	y              = flag.Int("y", 0, "Offset of posted image from top border")
 	order          = flag.String("order", "rtl", "Draw order (shuffle, ltr, rtl, ttb, btt)")
 	fetchImgPath   = flag.String("fetch", "", "Enable fetching the screen area to the given local file, updating it each second")
+	hevringImgPath = flag.String("hevring-preview", "", "Write the current task image to the given PNG file")
 	cpuprofile     = flag.String("cpuprofile", "", "Destination file for CPU Profile")
 )
 
@@ -83,7 +84,8 @@ func taskFromFlags(stop chan bool, wg *sync.WaitGroup) {
 	}
 
 	if startClient {
-		rpc.ConnectHevring(hev, stop, wg)
+		hevring := rpc.ConnectHevring(hev, stop, wg)
+		hevring.PreviewPath = *hevringImgPath
 	}
 
 	if fetchImg {

rpc/dottir.go

@@ -2,6 +2,7 @@ package rpc
 
 import (
 	"fmt"
+	"image"
 	"log"
 	"net"
 	"net/rpc"
@@ -9,9 +10,10 @@ import (
 	"time"
 
 	"github.com/SpeckiJ/Hochwasser/pixelflut"
+	"github.com/SpeckiJ/Hochwasser/render"
 )
 
-func ConnectHevring(ránAddress string, stop chan bool, wg *sync.WaitGroup) {
+func ConnectHevring(ránAddress string, stop chan bool, wg *sync.WaitGroup) *Hevring {
 	h := new(Hevring)
 	rpc.Register(h)
 
@@ -35,9 +37,12 @@ func ConnectHevring(ránAddress string, stop chan bool, wg *sync.WaitGroup) {
 		}
 		h.wg.Done()
 	}()
+
+	return h
 }
 
 type Hevring struct {
+	PreviewPath string
 	task        pixelflut.FlutTask
 	taskQuit    chan bool
 	quit        chan bool
@@ -63,6 +68,8 @@ func (h *Hevring) Flut(task pixelflut.FlutTask, reply *FlutAck) error {
 	h.taskQuit = make(chan bool)
 
 	go pixelflut.Flut(task, h.taskQuit, nil)
+	go h.savePreview(task.Img)
+
 	reply.Ok = true
 	return nil
 }
@@ -99,3 +106,13 @@ func (h *Hevring) Die(x int, reply *FlutAck) error {
 	reply.Ok = true
 	return nil
 }
+
+func (h Hevring) savePreview(img image.Image) {
+	if h.PreviewPath != "" && img != nil {
+		err := render.WriteImage(h.PreviewPath, img)
+		if err != nil {
+			fmt.Printf("[hevring] unable to write preview: %s\n", err)
+		}
+	}
+
+}