When an tile is rendered the writing to disk can be done in background

concurrently to the rendering of the next tile.

cmd/mtseeder/baselevel.go

@@ -30,10 +30,29 @@ func createTiles(
 	jobs chan blockPos,
 	done *sync.WaitGroup) {
 
-	defer done.Done()
-	defer btc.Close()
+	wFns := make(chan func() (bool, error))
+
+	// Writing already rendered tiles to disk can be done in background.
+	go func() {
+		for wfn := range wFns {
+			if _, err := wfn(); err != nil {
+				log.Printf("WARN: writing file failed: %v.\n", err)
+			}
+		}
+	}()
+
+	defer func() {
+		close(wFns)
+		btc.Close()
+		done.Done()
+	}()
+
 	for job := range jobs {
-		btc.CreateTile(job.x-1, job.z-1, job.i, job.j)
+		if err := btc.RenderArea(job.x-1, job.z-1); err != nil {
+			log.Printf("WARN: rendering failed: %v.\n", err)
+			continue
+		}
+		wFns <- btc.WriteFunc(job.i, job.j, nil)
 	}
 }
 
@@ -77,7 +96,7 @@ func createBaseLevel(
 		btc := common.NewBaseTileCreator(
 			client, colors, bg,
 			int16(yMin), int16(yMax),
-			transparent, baseDir, nil)
+			transparent, baseDir)
 		go createTiles(btc, jobs, &done)
 	}