ui: Add IsGamepadPresent

Fixes #447

examples/gamepad/main.go

@@ -32,11 +32,15 @@ const (
 )
 
 func update(screen *ebiten.Image) error {
-	// TODO: API to get the available, lowest ID
 	const gamepadID = 0
+	presences := [4]bool{}
 	axes := []string{}
 	pressedButtons := []string{}
 
+	for i := range presences {
+		presences[i] = ebiten.IsGamepadPresent(i)
+	}
+
 	maxAxis := ebiten.GamepadAxisNum(gamepadID)
 	for a := 0; a < maxAxis; a++ {
 		v := ebiten.GamepadAxis(gamepadID, a)
@@ -53,10 +57,21 @@ func update(screen *ebiten.Image) error {
 		return nil
 	}
 
-	str := `Gamepad
+	ids := []string{}
+	for i, p := range presences {
+		if p {
+			ids = append(ids, strconv.Itoa(i))
+		}
+	}
+
+	str := `Gamepad ({{.GamepadIDs}})
+
+Gamepad (ID: {{.GamepadID}}) status:
   Axes:
     {{.Axes}}
   Pressed Buttons: {{.Buttons}}`
+	str = strings.Replace(str, "{{.GamepadIDs}}", strings.Join(ids, ","), -1)
+	str = strings.Replace(str, "{{.GamepadID}}", strconv.Itoa(gamepadID), -1)
 	str = strings.Replace(str, "{{.Axes}}", strings.Join(axes, "\n    "), -1)
 	str = strings.Replace(str, "{{.Buttons}}", strings.Join(pressedButtons, ", "), -1)
 	ebitenutil.DebugPrint(screen, str)

input.go

@@ -56,6 +56,15 @@ func IsMouseButtonPressed(mouseButton MouseButton) bool {
 	return ui.CurrentInput().IsMouseButtonPressed(ui.MouseButton(mouseButton))
 }
 
+// IsGamepadPresent returns a boolean value indicating whether the gamepad for the given id exists.
+//
+// This function is concurrent-safe.
+//
+// NOTE: Gamepad API is available only on desktops, Chrome and Firefox.
+func IsGamepadPresent(id int) bool {
+	return ui.CurrentInput().IsGamepadPresent(id)
+}
+
 // GamepadAxisNum returns the number of axes of the gamepad (id).
 //
 // This function is concurrent-safe.

internal/ui/input.go

@@ -31,6 +31,15 @@ func (i *Input) CursorPosition() (x, y int) {
 	return adjustCursorPosition(i.cursorX, i.cursorY)
 }
 
+func (i *Input) IsGamepadPresent(id int) bool {
+	i.m.RLock()
+	defer i.m.RUnlock()
+	if len(i.gamepads) <= id {
+		return false
+	}
+	return i.gamepads[id].valid
+}
+
 func (i *Input) GamepadAxisNum(id int) int {
 	i.m.RLock()
 	defer i.m.RUnlock()
@@ -78,6 +87,7 @@ func (in *Input) Touches() []Touch {
 }
 
 type gamePad struct {
+	valid         bool
 	axisNum       int
 	axes          [16]float64
 	buttonNum     int

internal/ui/input_glfw.go

@@ -112,9 +112,12 @@ func (i *Input) update(window *glfw.Window, scale float64) {
 	i.cursorX = int(x / scale)
 	i.cursorY = int(y / scale)
 	for id := glfw.Joystick(0); id < glfw.Joystick(len(i.gamepads)); id++ {
+		i.gamepads[id].valid = false
 		if !glfw.JoystickPresent(id) {
 			continue
 		}
+		i.gamepads[id].valid = true
+
 		axes32 := glfw.GetJoystickAxes(id)
 		i.gamepads[id].axisNum = len(axes32)
 		for a := 0; a < len(i.gamepads[id].axes); a++ {

internal/ui/input_js.go

@@ -139,10 +139,12 @@ func (i *Input) updateGamepads() {
 	gamepads := nav.Call("getGamepads")
 	l := gamepads.Get("length").Int()
 	for id := 0; id < l; id++ {
+		i.gamepads[id].valid = false
 		gamepad := gamepads.Index(id)
 		if gamepad == js.Undefined || gamepad == nil {
 			continue
 		}
+		i.gamepads[id].valid = true
 
 		axes := gamepad.Get("axes")
 		axesNum := axes.Get("length").Int()