fixed app freezing on exit by saving project stuff in background on exit

ui.go

@@ -80,47 +80,45 @@ func main() {
 	heightmapPath := filepath.Join(appConfigDir, "heightmap.png")
 	bumpmapPath := filepath.Join(appConfigDir, "bumpmap.png")
 
-	// Save settings and images on window close
-	w.SetOnClosed(func() {
+	// Hide the window immediately on close, then save in the background.
+	closing := false
+	w.SetCloseIntercept(func() {
+		if closing {
+			return
+		}
+		closing = true
+
+		canvasSnapshot := canvasImg.Image
+		heightmapSnapshot := heightmapImg.Image
+		bumpmapSnapshot := bumpmapImg.Image
+
+		w.Hide()
+		go func() {
+			saveImage := func(path string, img image.Image, label string) {
+				if img == nil {
+					return
+				}
+				file, err := os.Create(path)
+				if err != nil {
+					log.Println("Failed to create "+label+" file:", err)
+					return
+				}
+				defer file.Close()
+				if err := png.Encode(file, img); err != nil {
+					log.Println("Failed to encode "+label+" image:", err)
+				}
+			}
+
 			if err := settings.Save(); err != nil {
 				log.Println("Error saving settings:", err)
 			}
-
-		if canvasImg.Image != nil {
-			canvasFile, err := os.Create(canvasPath)
-			if err != nil {
-				log.Println("Failed to create canvas file:", err)
-			} else {
-				defer canvasFile.Close()
-				if err := png.Encode(canvasFile, canvasImg.Image); err != nil {
-					log.Println("Failed to encode canvas image:", err)
-				}
-			}
-		}
-
-		if heightmapImg.Image != nil {
-			heightmapFile, err := os.Create(heightmapPath)
-			if err != nil {
-				log.Println("Failed to create heightmap file:", err)
-			} else {
-				defer heightmapFile.Close()
-				if err := png.Encode(heightmapFile, heightmapImg.Image); err != nil {
-					log.Println("Failed to encode heightmap image:", err)
-				}
-			}
-		}
-
-		if bumpmapImg.Image != nil {
-			bumpmapFile, err := os.Create(bumpmapPath)
-			if err != nil {
-				log.Println("Failed to create bumpmap file:", err)
-			} else {
-				defer bumpmapFile.Close()
-				if err := png.Encode(bumpmapFile, bumpmapImg.Image); err != nil {
-					log.Println("Failed to encode bumpmap image:", err)
-				}
-			}
-		}
+			saveImage(canvasPath, canvasSnapshot, "canvas")
+			saveImage(heightmapPath, heightmapSnapshot, "heightmap")
+			saveImage(bumpmapPath, bumpmapSnapshot, "bumpmap")
+			fyne.Do(func() {
+				a.Quit()
+			})
+		}()
 	})
 
 	// Load previously saved images