internal/ui: bug fix: show a black dot at the red button when needed

When SetWindowClosingHandled(true) is called, a black dot should be
shown at the red button to close the window.

Closes #3020

internal/ui/ui_darwin.go

@@ -238,6 +238,7 @@ var (
 	sel_origResizable                 = objc.RegisterName("isOrigResizable")
 	sel_setCollectionBehavior         = objc.RegisterName("setCollectionBehavior:")
 	sel_setDelegate                   = objc.RegisterName("setDelegate:")
+	sel_setDocumentEdited             = objc.RegisterName("setDocumentEdited:")
 	sel_setOrigDelegate               = objc.RegisterName("setOrigDelegate:")
 	sel_setOrigResizable              = objc.RegisterName("setOrigResizable:")
 	sel_toggleFullScreen              = objc.RegisterName("toggleFullScreen:")
@@ -433,3 +434,13 @@ func initializeWindowAfterCreation(w *glfw.Window) error {
 func (u *UserInterface) skipTaskbar() error {
 	return nil
 }
+
+// setDocumentEdited must be called from the main thread.
+func (u *UserInterface) setDocumentEdited(edited bool) error {
+	w, err := u.window.GetCocoaWindow()
+	if err != nil {
+		return err
+	}
+	objc.ID(w).Send(sel_setDocumentEdited, edited)
+	return nil
+}

internal/ui/ui_glfw.go

@@ -568,6 +568,22 @@ func (u *UserInterface) setWindowClosingHandled(handled bool) {
 	u.m.Lock()
 	u.windowClosingHandled = handled
 	u.m.Unlock()
+
+	if !u.isRunning() {
+		return
+	}
+	if u.isTerminated() {
+		return
+	}
+	u.mainThread.Call(func() {
+		if u.isTerminated() {
+			return
+		}
+		if err := u.setDocumentEdited(handled); err != nil {
+			u.setError(err)
+			return
+		}
+	})
 }
 
 // isFullscreen must be called from the main thread.
@@ -874,6 +890,13 @@ func (u *UserInterface) createWindow() error {
 		return err
 	}
 
+	u.m.Lock()
+	closingHandled := u.windowClosingHandled
+	u.m.Unlock()
+	if err := u.setDocumentEdited(closingHandled); err != nil {
+		return err
+	}
+
 	return nil
 }
 

internal/ui/ui_linbsd.go

@@ -200,3 +200,7 @@ func initializeWindowAfterCreation(w *glfw.Window) error {
 func (u *UserInterface) skipTaskbar() error {
 	return nil
 }
+
+func (u *UserInterface) setDocumentEdited(edited bool) error {
+	return nil
+}

internal/ui/ui_windows.go

@@ -242,6 +242,10 @@ func (u *UserInterface) skipTaskbar() error {
 	return nil
 }
 
+func (u *UserInterface) setDocumentEdited(edited bool) error {
+	return nil
+}
+
 func init() {
 	if microsoftgdk.IsXbox() {
 		// TimeBeginPeriod might not be defined in Xbox.