Part C of this demonstration takes the .xap project file you have created, and the ac- companying wave files, and loads them for playback in your game project. You can add the code from this section to either your 2D game or your 3D game project. For this section though, we are only going to focus on adding audio for ship0. Ship0’s en- gine, beep, and laser audio are appropriate for both 2D and 3D games because the audio is always positioned in front of the viewer.
After you add the code from section C, you will be able to hear the introduction when the game begins. When the introduction ends, the engine0 and telemetric beep0 of ship0 will play in an infinite loop. Whenever you accelerate, the engine volume and pitch increase. A laser will fire whenever you pull the right game-controller trigger or left-click the mouse.
Adding Audio
You can use the intro.wav, engine0.wav, engine1.wav, beep0.wav, beep1.wav, and fire.wav files in the Audio folder in the book’s download. You may use the audioProject.xap file you created, or you can find a copy in the Audio folder that is included in the book’s download. To reference these files in your project, add an Au- dio folder to your solution, add each of the .xap and wave files to it, and then refer- ence each file within the Audio folder from the Solution Explorer. At this point, the wave files are referenced in your project and are located in the Audio folder with your .xap project file. To enable audio in the code project, a reference is required at the top of your Game1.cs file to include the XACT audio library. This reference has already been added to your project by the XNA template wizard when the initial project shell was generated:
using Microsoft.Xna.Framework.Audio;
Since the focus of this section is to add audio for the intro and for ship0, you will need to declare sound cue objects to control each sound:
Cue ship0Cue, beep0Cue, introCue;
Some additional preparation in code is needed to store the different components of your audio system. As mentioned earlier, the project file will be referenced in the project and will generate the global settings file, the wave bank, and the sound bank.
Module-level declarations for loading and storing the sound engine, wave bank, and
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sound bank files will make these objects available for loading and playing your audio files throughout your game class:
private static AudioEngine soundEngine;
private static WaveBank waveBank;
private static SoundBank soundBank;
Your global settings, wave bank, and sound bank can now be loaded from the Initialize()method when the program begins. The file path specified leads to the same directory where your audioProject.xap project file is located. Even though these files are not physically present when your project is not running, the directory references are needed:
soundEngine =new AudioEngine("Content\\Audio\\audioProject.xgs");
waveBank =new WaveBank(soundEngine,"Content\\Audio\\Wave Bank.xwb");
soundBank =new SoundBank(soundEngine,"Content\\Audio\\Sound Bank.xsb");
At every frame, you must update the sound engine. If you omit this update, it may seem for many frames that your audio is working. However, Microsoft warns that without continuous updates, the sound engine will inevitably crash.
Before you actually update the sound engine, an additional check is made to en- sure that the sound engine exists. You use the sound engine’sIsDisposedproperty for this check. Trying to update the sound engine when it has been disposed will cause a program crash. To implement the sound engine update, add the following code to theUpdate()method:
if (!soundEngine.IsDisposed){
soundEngine.Update();
}
To ensure that your audio files unload when the program ends, add some code to dispose of them when the user exits from the program.DeleteAudio()will re- move your sound bank, wave bank, and engine from memory when the application is shut down:
void DeleteAudio(){
soundBank.Dispose();
waveBank.Dispose();
soundEngine.Dispose();
}
To ensure thatDeleteAudio()is called when the game ends, insideUpdate() ( just beforethis.Exit()) add a call statement to dispose of the audio:
DeleteAudio();
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The introduction sound plays once at the start of the program so the code that fol- lows is needed in the game class after the sound engine, wave bank, and sound bank are initialized insideInitialize()to retrieve the cue and to play it:
if (!soundEngine.IsDisposed){
introCue = soundBank.GetCue("intro");
introCue.Play();
}
When the introduction finishes, the ship0’s engine and beep start and repeat for the rest of the game. Before this happens though, the introduction Cue object’s IsPlayingattribute is used to determine if the introduction is still playing. When the introduction ends, a Boolean flag,gameStarted, is set totrue. To ensure that no other audio is played until after the introduction has finished, this variable decla- ration is added to the top of the game class:
private static bool gameStarted = false;
To enable proper timing for pausing and resuming audio and for playing the laser fire with the game pad, add class-level declarations for variables to compare press and release states for the game pad and mouse:
GamePadState gpCurrent, gpPrevious;
#if !XBOX
MouseState mouseCurrent, mousePrevious;
#endif
The gamer controls the firing noise by left-clicking the mouse or by pulling the right trigger. A new firing sound is only triggered whenever a new press event is regis- tered. In other words, a firing event is cleared to play when a press event in the current frame follows a release event from the previous frame. ThePlayCue()method is used to play the laser audio because it is a rapid-fire sound. ThePlayCue()method is not prone to disruptions to the audio, which can be caused by garbage collection that occurs with the GetCue() and Dispose() methods. The PlayCue() method requires that the cue be stored in memory for as long as the audio is needed during the game.
void Fire(){
if(gpCurrent.Triggers.Right!=0.0f && gpPrevious.Triggers.Right==0.0f
#if !Xbox
|| mouseCurrent.LeftButton == ButtonState.Pressed &&
mousePrevious.LeftButton != ButtonState.Pressed
#endif
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)
soundBank.PlayCue("fire");
}
As with theFire()method, when you’re coding the routine for toggling between the beep0’s paused and resumed states, a check is made for any newB-button press or new right-mouse-button press events. For each new press event, the beep’s pause and resume states are changed.PauseAndResumeBeep()is needed in the game class to enable this routine:
void PauseAndResumeBeep(){
if(
#if !Xbox
mouseCurrent.RightButton == ButtonState.Pressed
&& mousePrevious.RightButton == ButtonState.Released ||
#endif
gpCurrent.Buttons.B == ButtonState.Pressed
&& gpPrevious.Buttons.B == ButtonState.Released){
if (!beep0Cue.IsPaused)
soundEngine.GetCategory("Beep0").Pause(); // pause beep else if (beep0Cue.IsPaused)
soundEngine.GetCategory("Beep0").Resume(); // play beep }
}
In part A of this example, you created a cue instance variable to control ship0’s en- gine volume and pitch from code. You must add theGetAccelerationVolume() method to the game class to implement the first part of this routine to generate the level of acceleration that drives these values:
float GetAccelerationVolume(){
float accelerate, accelerateX, accelerateY;
accelerate = 0.0f;
// left stick forward, back, or side shift sets acceleration volume if (GamePad.GetState(PlayerIndex.One).IsConnected){
accelerateX =
Math.Abs(GamePad.GetState(PlayerIndex.One).ThumbSticks.Left.X);
accelerateY =
Math.Abs(GamePad.GetState(PlayerIndex.One).ThumbSticks.Left.Y);
accelerate = Math.Max(accelerateX, accelerateY);
}
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// no controller so use arrow keys to set acceleration volume else{
KeyboardState kbState = Keyboard.GetState();
if (kbState.IsKeyDown(Keys.Right)|| kbState.IsKeyDown(Keys.D)
|| kbState.IsKeyDown(Keys.Left) || kbState.IsKeyDown(Keys.A)
|| kbState.IsKeyDown(Keys.Up) || kbState.IsKeyDown(Keys.W)
|| kbState.IsKeyDown(Keys.Down) || kbState.IsKeyDown(Keys.S)){
accelerate = 1.0f;
} }
return accelerate;
}
After the introduction begins inside theInitialize() method, the code for driving the sound events in each frame is called from theUpdate()method. Before anything is done in this routine, a check is made to ensure that the audio engine actu- ally exists. Failing to check whether this object exists will cause the program to crash if the sound banks or cues are used after the audio engine has been disposed.
The engine0 and telemetric beep0 are started only after the introduction finishes.
When the program begins, a check is made each frame to determine whether the in- troduction is playing. When the introduction’sIsPlayingattribute isfalse, the engine0 audio and beep0 audio are started and a Boolean flag is set so that this condi- tion is never entered again during the game.
Once the audio has started, checks are made each frame to update the accelera- tion, handle any trigger firing, and to pause and resume beeping:
if (!gameStarted){
if (!soundEngine.IsDisposed){
if (!introCue.IsPlaying){ // intro over gameStarted = true;
beep0Cue = soundBank.GetCue("beep0"); // play beep0 soundBank.PlayCue("beep0"); // lower volume soundEngine.GetCategory("Beep0").SetVolume(0.1f);
ship0Cue = soundBank.GetCue("engine0"); // start engine 0 ship0Cue.Play();
} } } else{
if (!soundEngine.IsDisposed){
#if !XBOX // update mouse state
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mousePrevious = mouseCurrent;
mouseCurrent = Mouse.GetState();
#endif
gpPrevious = gpCurrent; // update gamepad states gpCurrent = GamePad.GetState(PlayerIndex.One);
Fire(); // check input for fire
// change volume with acceleration ship0Cue.SetVariable("Engine0Variable", GetAccelerationVolume());
PauseAndResumeBeep(); // for beep 0 with ship 0 }
}
If you run your code now, you will hear the introduction play first, and then you will hear ship0’s engine and telemetric beep. You will also hear the firing sound every time you pull the right trigger or left-click the mouse. Ship0’s engine audio will rise in volume and pitch every time you accelerate.