ui: Add IsForeground API to glfw driver (#1058)

Updates #1037

internal/driver/ui.go

@@ -37,6 +37,7 @@ type UI interface {
 	DeviceScaleFactor() float64
 	CursorMode() CursorMode
 	IsFullscreen() bool
+	IsForeground() bool
 	IsRunnableInBackground() bool
 	IsVsyncEnabled() bool
 	ScreenSizeInFullscreen() (int, int)

internal/uidriver/glfw/ui.go

@@ -402,6 +402,19 @@ func (u *UserInterface) SetFullscreen(fullscreen bool) {
 	u.setWindowSize(w, h, fullscreen, u.vsync)
 }
 
+func (u *UserInterface) IsForeground() bool {
+	if !u.isRunning() {
+		return false
+	}
+
+	var foreground bool
+	_ = u.t.Call(func() error {
+		foreground = u.window.GetAttrib(glfw.Focused) == glfw.True
+		return nil
+	})
+	return foreground
+}
+
 func (u *UserInterface) SetRunnableInBackground(runnableInBackground bool) {
 	u.setRunnableInBackground(runnableInBackground)
 }

internal/uidriver/js/ui.go

@@ -76,6 +76,11 @@ func (u *UserInterface) IsFullscreen() bool {
 	return false
 }
 
+func (u *UserInterface) IsForeground() bool {
+	// TODO: implement this
+	return true
+}
+
 func (u *UserInterface) SetRunnableInBackground(runnableInBackground bool) {
 	u.runnableInBackground = runnableInBackground
 }

internal/uidriver/mobile/ui.go

@@ -369,6 +369,11 @@ func (u *UserInterface) SetFullscreen(fullscreen bool) {
 	// Do nothing
 }
 
+func (u *UserInterface) IsForeground() {
+	// TODO: implement this
+	return true
+}
+
 func (u *UserInterface) IsRunnableInBackground() bool {
 	return false
 }

run.go

@@ -346,6 +346,16 @@ func SetFullscreen(fullscreen bool) {
 	uiDriver().SetFullscreen(fullscreen)
 }
 
+// IsForeground returns a boolean value indicating whether
+// the game is in focus or in the foreground.
+//
+// IsForeground will only return true if IsRunnableInBackground is false.
+//
+// IsForeground is concurrent-safe.
+func IsForeground() bool {
+	return uiDriver().IsForeground()
+}
+
 // IsRunnableInBackground returns a boolean value indicating whether
 // the game runs even in background.
 //