11 Getting Player Input Using a Gamepad Session 3.1

11

Getting Player Input Using a Gamepad

Session 3.1

Session Overview

Introduce the gamepad device

Show how a C# object can be used to represent the state of a gamepad

Find out how to use the properties of the GamePadState object in a program

Create a Mood Light that is controlled by the gamepad

Discover how to use logical operators OR and AND

Create our first XNA multiplayer game

Chapter 3.1: Getting Player Input Using a Gamepad 2

A User-Controlled Mood Light

We are going to make a Mood Light that is controlled by the user

They will press the buttons on the gamepad to control the brightness and color of the screen background

The user can select any color that they want

This can also serve as the basis of a game

To do this we need to know how XNA games get input from the player


The Xbox Gamepad

The gamepad is a very complex device

It is connected to the host either by USB or a wireless connection

It can be used with a Windows PC or an Xbox

You can obtain a wireless adapter for the Windows PC


The Zune Buttons

The Zune buttons work in the same way as the buttons on a gamepad

The same XNA program can work with a gamepad or a Zune

However, the Zune doesn’t provide all the buttons that a gamepad does


Software and Objects

We know that C# programs are made up of objects that bring together data and behaviors A game has Game World data and draw and update methods

The state of a gamepad can be represented by a C# object called a GamePadState object

This contains the information about the state of the gamepad at a particular instant

The GamePadState object also provides properties you can use to read this status information


The GamePadState object

A GamePadState object contains information about all the input devices the gamepad has

We are going to consider just the buttons and the DPad at the moment

When the Red button (B) is pressed we want the redIntensity value of the background color to increase


GamePadState

Buttons

DPad

Creating a GamePadState Variable

The game will use a variable to hold the state of the gamepad

It will then test the values of the buttons in this variable so that the gamepad can be used to control the game

The variable must be declared like any other variable in the game program

It has been given the identifier pad1


GamePadState pad1;GamePadState pad1;

The pad1 Variable

Each time that update is called, the pad1 variable is set with the state of the gamepad for player 1

Code in the update method will use this variable

Should the pad1 variable be a local variable or a member of the Game1 class? Member variables are shared between all the

methods in a class

Local variables are just used inside the body of a method and discarded when no longer required


Using Local Variables

The variable pad1 should be local to the update method

We don’t want to retain the value of gamepad states from previous calls of update

No other methods need to use the value of pad1

Deciding which variables should be local and which should be members is part of the program design process


Setting the pad1 Variable

We can set the value of pad1 when we declare it

The XNA Framework provides a class called GamePad that exposes a getState method

The getState method is told which gamepad to get the state of

We don’t need to know how getState works, just how to call it and what the type of the result is


GamePadState pad1 = GamePad.GetState (PlayerIndex.One) ;GamePadState pad1 = GamePad.GetState (PlayerIndex.One) ;

GamePadState Properties

A property is member of a class that represents some data in the class

They can be set up to be read or written, or both

The GamePadState properties can only be read

Each of the properties can contain several values


GamePadState

Buttons

DPad

Game Update Behavior

This condition tests the state of the B (Red) button

If the button is Pressed the condition adds 1 to the value of redIntensity

If the button is held down successive calls of update will cause the redIntensity to increase

The equality operator is used because we are comparing the state of Buttons.B with the value ButtonState.Pressed


if (pad1.Buttons.B == ButtonState.Pressed) redIntensity++;if (pad1.Buttons.B == ButtonState.Pressed) redIntensity++;

Game Update Behavior

This is the code that allows a game to control the red intensity using button B on a gamepad Create a local variable called pad1 that

contains the state of the gamepad for player 1

Get the state of button B out of the Buttons in the pad, and if the button is pressed, increase the value of redIntensity.


GamePadState pad1 = GamePad.GetState(PlayerIndex.One);

if (pad1.Buttons.B == ButtonState.Pressed) redIntensity++;


if (pad1.Buttons.B == ButtonState.Pressed) redIntensity++;

1. User-Controlled Red Light


This version of Mood Light uses the code above to control the redIntensity value

When the Red button is pressed the screen redIntensity value gets larger

Kris Athi

added "in the Game1.cs file." to step 3 in the instructor notes

Controlling Green and Blue

The same code construction can be used to control the green and blue intensity values

Note that we don’t need to get a new GamePadState value each time, the program can just read different properties from the same pad1 value



if (pad1.Buttons.B == ButtonState.Pressed) redIntensity++;if (pad1.Buttons.A == ButtonState.Pressed) greenIntensity++;if (pad1.Buttons.X == ButtonState.Pressed) blueIntensity++;


if (pad1.Buttons.B == ButtonState.Pressed) redIntensity++;if (pad1.Buttons.A == ButtonState.Pressed) greenIntensity++;if (pad1.Buttons.X == ButtonState.Pressed) blueIntensity++;

Controlling Yellow Intensity Using the Y Button

The gamepad has a Yellow button (Y)

We can increase the yellow intensity by increasing both red and green when this button is pressed

To achieve this, the two update statements must be placed in a block after the condition


if (pad1.Buttons.Y == ButtonState.Pressed) { redIntensity++; greenIntensity++;}

if (pad1.Buttons.Y == ButtonState.Pressed) { redIntensity++; greenIntensity++;}

2. User-Controlled Light


This version of Mood Light uses all the gamepad buttons to control the background color

Kris Athi


Adding Zune Support Using the DPad

The Zune does not have all of the buttons on the gamepad

However it does have a DPad which can be pressed in one of four directions

We could make a “Mood Flashlight” by using the DPad to control the colors

Then the program would work on the Zune as well


Controlling Red Using the DPad.Right Value

The GamePadState type contains a DPad property which gives the states of the Left, Right, Up, and Down positions of the DPad

These are used in exactly the same way as the colored buttons on the gamepad

If any button state is equal to the value ButtonState.Pressed it means that the direction is selected on the gamepad


if (pad1.DPad.Right == ButtonState.Pressed) redIntensity++;if (pad1.DPad.Right == ButtonState.Pressed) redIntensity++;

Andrew

AU/ED: This note has the same text as an earlier slide in this presentation, is that okay?

Combining Tests Using Logical OR

We want to make the red light brighter if button B (Red) is pressed or Right is pressed on the DPad

We can do this by having two separate if statements

However, it would be neater to be able to use a single condition:

“If Button B is pressed OR DPad Right is pressed increase the value of redIntensity”

C# provides a logical operator to allow this

We must use the logical OR operator


The Logical OR operator

The logical OR operator is two vertical bars - ||

It works between Boolean values (i.e. true or false)

If either of the values on each side are true, the result it gives is true

The above code increases redIntensity if either button is pressed


if (pad1.DPad.Right == ButtonState.Pressed || pad1.Buttons.B == ButtonState.Pressed){ redIntensity++;}

if (pad1.DPad.Right == ButtonState.Pressed || pad1.Buttons.B == ButtonState.Pressed){ redIntensity++;}

Logical OR Test

Logical OR works between any two conditions that return a Boolean result

We can use it between the values true and false Although this might result in compiler warnings

Which of the above statements would increase the value of redIntensity?


if (true || false ) redIntensity++;if (true || true ) redIntensity++;if (false|| false ) redIntensity++;

if (true || false ) redIntensity++;if (true || true ) redIntensity++;if (false|| false ) redIntensity++;

Logical OR Test

The OR operator returns true if either of the conditions on each side of the operator is true

Therefore it only returns false if both the conditions are false


if (true || false ) redIntensity++; // increasesif (true || true ) redIntensity++; // increasesif (false || false ) redIntensity++; // doesn’t increase

if (true || false ) redIntensity++; // increasesif (true || true ) redIntensity++; // increasesif (false || false ) redIntensity++; // doesn’t increase

Logical AND

There is also a logical AND operator

We could use this to make the program reset all the colors to 0 if both triggers are pressed on the gamepad This makes it harder to reset the colors by

mistake

The logical AND condition only works out to true if the conditions on both sides are true

The logical AND operator is the character sequence &&


Logical AND Value Reset

The program can test the values of the shoulder buttons on the controller

If both of them are pressed the block of code is performed

This resets the intensity values to 0


if (pad1.Buttons.LeftShoulder == ButtonState.Pressed && pad1.Buttons.RightShoulder == ButtonState.Pressed){ redIntensity = 0; greenIntensity = 0; blueIntensity = 0;}

if (pad1.Buttons.LeftShoulder == ButtonState.Pressed && pad1.Buttons.RightShoulder == ButtonState.Pressed){ redIntensity = 0; greenIntensity = 0; blueIntensity = 0;}

3. Fully Functional Light


This version of the Mood Light will work on Zune, Windows PC or Xbox

It also provides the reset behavior with the shoulder buttons

Kris Athi


Game Idea – Color Nerve

You can use this program as the basis of a game: Players take turns to press any buttons they like

on the gamepad (but they must change the color on the screen)

If the screen flashes from bright to dark (i.e. an intensity value wraps around) during a turn that player is out

The game continues until one player is left to become the winner

Press the shoulder buttons to reset for the next game


Summary

The XNA Framework uses the type GamePadState to represent the state of a gamepad in a game

The GamePad class, which is part of XNA, provides a getState method that can be used to get the GamePadState value for the selected player

The GamePadState type exposes properties that can be read to get the state of the gamepad

These states can be combined using logical operators to allow more complicated behaviors to be created in a program


True/False Revision Quiz

An XNA program can control the state of the buttons on a gamepad.

The GamePadState type holds information about the state of a gamepad.

Objects can expose information by means of properties.

An XNA program can only connect to one gamepad.

The Zune has a full set of colored buttons.

The AND operator is represented by|| in a program.
































The AND operator is represented by||in a program.


















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11 Getting Player Input Using a Gamepad Session 3.1