XNA Game Studio 4.0 : Xbox 360 Gamepad (part 1) - Reading Gamepad State

The Xbox 360 gamepad is the controller that is included when you purchase an Xbox 360. It comes in both a wired and wireless model with several colors available to choose from (see Figure 1).

Figure 1. Xbox 360 wireless controller

The Xbox 360 gamepad features several analog and digital inputs, including face buttons, a direction pad, two thumb sticks, two triggers, and the circular Xbox 360 guide button in the center. The guide button is reserved and input from it is not available through the XNA Game Studio APIs. Along with input, the Xbox 360 gamepad also offers the capability to give force feedback to the user in the form of two vibration motors in the controller. The Xbox 360 gamepad can be used with a Windows PC. Wired controllers can plug directly into the PC using the USB connection. Wireless gamepads require a PC wireless receiver designed for the Xbox 360 wireless controller. Windows Phone does not support the Xbox 360 gamepad.

Note

When you create a new XNA Game Studio project, look at the Update method. It contains code that checks whether the Back button has been pressed and if it has to call exit on the game.

Although Windows Phone does not support the Xbox 360 gamepad, there is one exception. The physical back button on Windows Phones is reported as the Back button on the controller for PlayerIndex.One.

Reading Gamepad State

Just as with keyboard and mouse input, the gamepad input is read by polling the current state of a gamepad. The GamePad.GetState method is used to return the GamePadState structure, which can then be used to determine what buttons are currently pressed and the location of the thumb sticks and triggers. Tables 1 and 2 contain the methods and properties exposed by the GamePadState structure.

Table 1. Methods of GamePadState

Method	Description
IsButtonDown	Returns true if the provided button is currently pressed
IsButtonUp	Returns true if the provided button is not currently pressed

Table 2. Properties of GamePadState

Property	Type	Description
Buttons	GamePadButtons	Structure that contains the state of all gamepad buttons
DPad	GamePadDPad	Structure that contains the state of all DPad buttons
ThumbSticks	GamePadThumbSticks	Structure that contains the position values for left and right thumb sticks
Triggers	GamePadTriggers	Structure that contains the position of the left and right triggers
IsConnected	bool	Returns true if the gamepad is connected
PacketNumber	int	Identifier

To read the current state of a gamepad, add the following line of code to your game’s Update method:

GamePadState currentGamePadState = GamePad.GetState(PlayerIndex.One);

The GetState method requires a PlayerIndex. In this case, we request the first player’s gamepad state. The Xbox 360 gamepad features four lights around the center guide button that displays the gamepads current PlayerIndex.

Reading Gamepad Buttons

Now that you have the current state of the gamepad, you can check whether any of the buttons are pressed by using the GamePadState.Buttons property. Buttons returns a GamePadButtons structure, which contains properties for all of the buttons supported by gamepads. These properties all are of the ButtonState type, which is the same used for the mouse buttons. Table 3 contains the list of properties exposed by the GamePadButtons structure.

Table 3. Properties of GamePadButtons

Property	Type	Description
A	ButtonState	Pressed state of the A button
B	ButtonState	Pressed state of the B button
X	ButtonState	Pressed state of the X button
Y	ButtonState	Pressed state of the Y button
Back	ButtonState	Pressed state of the Back button
Start	ButtonState	Pressed state of the Start button
LeftShoulder	ButtonState	Pressed state of the Left Shoulder button
RightShoulder	ButtonState	Pressed state of the Right Shoulder button
LeftStick	ButtonState	Pressed state of the Left Stick button
RightStick	ButtonState	Pressed state of the Right Stick button
BigButton	ButtonState	Pressed state of the Big Button

Gamepad State Packet Numbers

If you call GamePad.GetState in a tight loop, you might receive the same state more than once. If you are concerned that you might call GetState too quickly, check the PacketNumber property on each GamePadState to verify that the numbers are different. States with the same PacketNumber represent that the device state has not updated.

To determine whether the GamePad buttons are pressed, add the following lines of code to your game:

// Determine if the A button has been pressed
if (currentGamePadState.Buttons.A == ButtonState.Pressed)
{
    // A button is pressed
}
if (currentGamePadState.Buttons.Start == ButtonState.Pressed)
{
    // Start button is pressed
}
if (currentGamePadState.Buttons.RightShoulder == ButtonState.Pressed)
{
    // Right shoulder button is pressed
}
if (currentGamePadState.Buttons.LeftStick == ButtonState.Pressed)
{
    // Left stick is clicked down
}

Some of these buttons are straightforward. The letter buttons A, B, X, and Y correspond to the face buttons on the right side of the controller with the same letter. The Back and Start buttons are to the left and right of the guide buttons in the center of the controller. The LeftShoulder and RightShoulder buttons are the thin buttons on the top left and right of the gamepad. The LeftStick and RightStick are buttons that set when a player depresses the left and right stick into the controller. The GamePadButtons structure also contains a property called BigButton. This button is available on a different type of Xbox 360 gamepad called the Big Button controller.

Reading Gamepad Direction Pad

Along with the face buttons, the Xbox 360 gamepad offers digital input from a directional pad on the left side of the controller. The GamePad.DPad property returns a GamePadDPad structure, which contains ButtonState properties for the Up, Down, Left, and Right directions. Table 4 contains a list properties exposed by the GamePadDPad structure.

Table 4. Properties of GamePadDPad

Property	Type	Description
Up	ButtonState	Pressed state of the Up DPad direction
Down	ButtonState	Pressed state of the Down DPad direction
Left	ButtonState	Pressed state of the Left DPad direction
Right	ButtonState	Pressed state of the Right DPad direction

To determine whether the directions are pressed, use the following lines of code:

// Determine if DPad directions are being pressed
if (currentGamePadState.DPad.Left == ButtonState.Pressed)
{
    // Left DPad button is pressed
}
else if (currentGamePadState.DPad.Right == ButtonState.Pressed)
{
    // Right DPad button is pressed
}
if (currentGamePadState.DPad.Up == ButtonState.Pressed)
{
    // Up DPad button is pressed
}
else if (currentGamePadState.DPad.Down == ButtonState.Pressed)
{
    // Down DPad button is pressed
}

It is important to use else if conditions only on directions that are opposite from one another. It is possible to have two directions pressed if they are next to each other. For example, a user can press Down and Right at the same time.

Reading Gamepad Thumb Sticks

The gamepad has four analog states: two for the left and right thumb sticks and two for the left and right triggers. To read the state of the thumb sticks, use the GamePadState.GamePadThumbSticks property. The GamePadThumbSticks structure contains two properties: Left and Right both of which return Vector2 values. The Vector2 value represents the thumb stick displacement in the X and Y directions. These floating points range from –1.0 to 1.0. Table 5 contains a list of properties exposed by the GamePadThumbSticks structure.

Table 5. Properties of GamePadThumbSticks

Property	Type	Description
Left	Vector2	Position of the left thumb stick
Right	Vector2	Position of the right thumb stick

To read the current X and Y position of the left thumb stick, use the following line of code:

Vector2 leftThumbStick = currentGamePadState.ThumbSticks.Left;

Reading Gamepad Triggers

Finally, the last type of gamepad state are the triggers. To read the current trigger position, use the GamePadState.Triggers property. It returns a GamePadTriggers structure, which contains two float values in the Left and Right properties. Each triggers value is from 0.0, which indicates not depressed, to 1.0, which indicates that the trigger is fully depressed. Table 6 contains a list of the properties exposed by the GamePadTriggers structure.

Table 6. Properties of GamePadTriggers

Property	Type	Description
Left	float	Position of the left trigger depression
Right	float	Position of the right trigger depression

To read the current position of the right trigger, use the following line of code:

float rightTrigger = currentGamePadState.Triggers.Right;