inpututil: Replace JustDisconnectedGamepadIDs with IsGamepadJustDisconnected (#505)

examples/gamepad/main.go

@@ -32,12 +32,21 @@ const (
 	screenHeight = 480
 )
 
+var (
+	gamepadIDs = map[int]struct{}{}
+)
+
 func update(screen *ebiten.Image) error {
+	// Log the gamepad connection events.
 	for _, id := range inpututil.JustConnectedGamepadIDs() {
 		log.Printf("gamepad connected: id: %d", id)
+		gamepadIDs[id] = struct{}{}
 	}
-	for _, id := range inpututil.JustDisconnectedGamepadIDs() {
+	for id := range gamepadIDs {
+		if inpututil.IsGamepadJustDisconnected(id) {
 			log.Printf("gamepad disconnected: id: %d", id)
+			delete(gamepadIDs, id)
+		}
 	}
 
 	ids := ebiten.GamepadIDs()
@@ -56,7 +65,7 @@ func update(screen *ebiten.Image) error {
 				pressedButtons[id] = append(pressedButtons[id], strconv.Itoa(int(b)))
 			}
 
-			// Log some events.
+			// Log button events.
 			if inpututil.IsGamepadButtonJustPressed(id, b) {
 				log.Printf("button pressed: id: %d, button: %d", id, b)
 			}

inpututil/inpututil.go

@@ -243,22 +243,16 @@ func JustConnectedGamepadIDs() []int {
 	return ids
 }
 
-// JustDisconnectedGamepadIDs returns gamepad IDs that are disconnected just in the current frame.
+// IsGamepadJustDisconnected returns a boolean value indicating
+// whether the gamepad of the given id is released just in the current frame.
 //
-// JustDisconnectedGamepadIDs might return nil when there is no disconnected gamepad.
-//
-// JustDisconnectedGamepadIDs is concurrent safe.
-func JustDisconnectedGamepadIDs() []int {
-	var ids []int
+// IsGamepadJustDisconnected is concurrent safe.
+func IsGamepadJustDisconnected(id int) bool {
 	theInputState.m.RLock()
-	for id := range theInputState.prevGamepadIDs {
-		if _, ok := theInputState.gamepadIDs[id]; !ok {
-			ids = append(ids, id)
-		}
-	}
+	_, prev := theInputState.prevGamepadIDs[id]
+	_, current := theInputState.gamepadIDs[id]
 	theInputState.m.RUnlock()
-	sort.Ints(ids)
-	return ids
+	return prev && !current
 }
 
 // IsGamepadButtonJustPressed returns a boolean value indicating