examples/dropfile: bug fix: handle errors correctly

examples/dropfile/main.go

@@ -25,13 +25,24 @@ import (
 )
 
 type Game struct {
-	imageMutex sync.Mutex
 	images []*ebiten.Image
+	err    error
+
+	m sync.Mutex
 }
 
 func (g *Game) Update() error {
+	if err := func() error {
+		g.m.Lock()
+		defer g.m.Unlock()
+		return g.err
+	}(); err != nil {
+		return err
+	}
+
 	if files := ebiten.DroppedFiles(); files != nil {
-		go fs.WalkDir(files, ".", func(path string, d fs.DirEntry, err error) error {
+		go func() {
+			if err := fs.WalkDir(files, ".", func(path string, d fs.DirEntry, err error) error {
 				if err != nil {
 					return err
 				}
@@ -46,7 +57,9 @@ func (g *Game) Update() error {
 				if err != nil {
 					return err
 				}
-			defer f.Close()
+				defer func() {
+					_ = f.Close()
+				}()
 
 				img, err := png.Decode(f)
 				if err != nil {
@@ -54,19 +67,26 @@ func (g *Game) Update() error {
 				}
 				eimg := ebiten.NewImageFromImage(img)
 
-			g.imageMutex.Lock()
+				g.m.Lock()
 				g.images = append(g.images, eimg)
-			g.imageMutex.Unlock()
+				g.m.Unlock()
 
 				return nil
-		})
+			}); err != nil {
+				g.m.Lock()
+				if g.err == nil {
+					g.err = err
+				}
+				g.m.Unlock()
+			}
+		}()
 	}
 	return nil
 }
 
 func (g *Game) Draw(screen *ebiten.Image) {
-	g.imageMutex.Lock()
+	g.m.Lock()
-	defer g.imageMutex.Unlock()
+	defer g.m.Unlock()
 
 	if len(g.images) == 0 {
 		ebitenutil.DebugPrint(screen, "Drop PNG files onto this window!")