手把手教用XNA开发winphone7游戏（三）

XNA Game Studio 游戏循环

在这部分中您将重点两剩余部分的游戏 — — 重写Update 和 Draw 功能。有些大大可能看过相关微软的训练包，我这里主要是帮一些初学者。希望各位大大包含，毕竟文章发出来还是有工作量的。大家觉得有用就好，要是没有耽误时间给大家道个歉。（感谢http://winphone.us/）

1.       打开 BackgroundScreen.cs文件。

2.       重写基类Update 方法如下:

(Code Snippet – Game Development with XNA – Background Screen Update method)

C#

public override void Update(GameTime gameTime, bool otherScreenHasFocus,

                  bool coveredByOtherScreen)

{

   base.Update(gameTime, otherScreenHasFocus, false);

}

 

3.       重写基类方法绘制。 绘图方法将绘制图形设备上使用 Microsoft.Xna.Framewok.Graphics 命名空间中的 SpriteBatch 类。一组sprites被绘制的时候使用同样的设置。改变 Draw 方法来匹配下面的代码段：

(Code Snippet – Game Development with XNA – Background Screen Draw method)

C#

public override void Draw(GameTime gameTime)

{

   SpriteBatch spriteBatch = ScreenManager.SpriteBatch;

 

   // Make the menu slide into place during transitions, using a

   // power curve to make things look more interesting (this makes

   // the movement slow down as it nears the end).

   float transitionOffset =      (float)Math.Pow(TransitionPosition, 2);

 

   spriteBatch.Begin();

 

   // Draw Background

   spriteBatch.Draw(background, new Vector2(0, 0),

     new Color(255, 255, 255, TransitionAlpha));

 

   // Draw Title

   spriteBatch.Draw(title, new Vector2(60, 55),

     new Color(255, 255, 255, TransitionAlpha));

 

   spriteBatch.End();

}

 

4.       按 F5 编译并运行该应用程序。

图1

修改了updatae和Draw后的运行效果 

5.       停止调试 (SHIFT + F5)，并返回到编辑应用程序。

6.       将一个附加类添加到应用程序，并将其名称设置为 GameplayScreen。

Note: 要创建一个新的类，在解决方案资源管理器中右键单击 AlienGame 项目并选择Add | Class.

 

7.       添加以下使用申明到新类：

(Code Snippet – Game Development with XNA – Gameplay Screen using statements )

C#

using AlienGameSample;

using Microsoft.Xna.Framework;

using Microsoft.Xna.Framework.Graphics;

using Microsoft.Xna.Framework.Audio;

using System.IO.IsolatedStorage;

using System.IO;

 

8.       从 GameScreen 派生：

C#

class GameplayScreen : GameScreen

{

}

 

9.       添加以下类变量 （将在比赛中使用它们）。 后面我们使用这些变量，处理游戏逻辑、 用户输入和绘图：

(Code Snippet – Game Development with XNA – Gameplay Screen variables)

C#

//

// Game Play Members

//

Rectangle worldBounds;

bool gameOver;

int baseLevelKillCount;

int levelKillCount;

float alienSpawnTimer;

float alienSpawnRate;

float alienMaxAccuracy;

float alienSpeedMin;

float alienSpeedMax;

int alienScore;

int nextLife;

int hitStreak;

int highScore;

Random random;

 

//

// Rendering Members

//

Texture2D cloud1Texture;

Texture2D cloud2Texture;

Texture2D sunTexture;

Texture2D moonTexture;

Texture2D groundTexture;

Texture2D tankTexture;

Texture2D alienTexture;

Texture2D badguy_blue;

Texture2D badguy_red;

Texture2D badguy_green;

Texture2D badguy_orange;

Texture2D mountainsTexture;

Texture2D hillsTexture;

Texture2D bulletTexture;

Texture2D laserTexture;

 

SpriteFont scoreFont;

SpriteFont menuFont;

 

Vector2 cloud1Position;

Vector2 cloud2Position;

Vector2 sunPosition;

 

// Level changes, nighttime transitions, etc

float transitionFactor; // 0.0f == day, 1.0f == night

float transitionRate; // > 0.0f == day to night

 

ParticleSystem particles;

 

//

// Audio Members

//

SoundEffect alienFired;

SoundEffect alienDied;

SoundEffect playerFired;

SoundEffect playerDied;

 

//Screen dimension consts

const float screenHeight = 800.0f;

const float screenWidth = 480.0f;

const int leftOffset = 25;

const int topOffset = 50;

const int bottomOffset = 20;

 

10.   游戏类构造函数定义 (在游戏屏幕和其他屏幕在游戏中的) 之间的屏幕转换的速度和大小—— 在处理游戏的所有操作的地方。 添加此类构造函数，如下所示：:

(Code Snippet – Game Development with XNA – Gameplay Screen Constructor)

C#

public GameplayScreen()

{

   random = new Random();

 

   worldBounds = new Rectangle(0, 0, (int)screenWidth, (int)screenHeight);

 

   gameOver = true;

 

   TransitionOnTime = TimeSpan.FromSeconds(0.0);

   TransitionOffTime = TimeSpan.FromSeconds(0.0);

}

 

11.   现在让我们来创建内容的加载和卸载功能。 重写基类的 LoadContent 和 UnloadContent 的方法。

添加 LoadContent 代码段：:

(Code Snippet – Game Development with XNA – Gameplay Screen LoadContent method)

C#

public override void LoadContent()

{

    cloud1Texture = ScreenManager.Game.Content.Load<Texture2D>("cloud1");

    cloud2Texture = ScreenManager.Game.Content.Load<Texture2D>("cloud2");

    sunTexture = ScreenManager.Game.Content.Load<Texture2D>("sun");

    moonTexture = ScreenManager.Game.Content.Load<Texture2D>("moon");

    groundTexture = ScreenManager.Game.Content.Load<Texture2D>("ground");

    tankTexture = ScreenManager.Game.Content.Load<Texture2D>("tank");

    mountainsTexture = ScreenManager.Game.Content.Load<Texture2D>("mountains_blurred");

    hillsTexture = ScreenManager.Game.Content.Load<Texture2D>("hills");

    alienTexture = ScreenManager.Game.Content.Load<Texture2D>("alien1");

    badguy_blue = ScreenManager.Game.Content.Load<Texture2D>("badguy_blue");

    badguy_red = ScreenManager.Game.Content.Load<Texture2D>("badguy_red");

    badguy_green = ScreenManager.Game.Content.Load<Texture2D>("badguy_green");

    badguy_orange = ScreenManager.Game.Content.Load<Texture2D>("badguy_orange");

    bulletTexture = ScreenManager.Game.Content.Load<Texture2D>("bullet");

    laserTexture = ScreenManager.Game.Content.Load<Texture2D>("laser");

    alienFired = ScreenManager.Game.Content.Load<SoundEffect>("Tank_Fire");

    alienDied = ScreenManager.Game.Content.Load<SoundEffect>("Alien_Hit");

    playerFired = ScreenManager.Game.Content.Load<SoundEffect>("Tank_Fire");

    playerDied = ScreenManager.Game.Content.Load<SoundEffect>("Player_Hit");

    scoreFont = ScreenManager.Game.Content.Load<SpriteFont>("ScoreFont");

    menuFont = ScreenManager.Game.Content.Load<SpriteFont>("MenuFont");

 

    cloud1Position = new Vector2(224 - cloud1Texture.Width, 32);

    cloud2Position = new Vector2(64, 80);

 

    sunPosition = new Vector2(16, 16);

 

    particles = new ParticleSystem(ScreenManager.Game.Content, ScreenManager.SpriteBatch);

 

    base.LoadContent();

}

 

12.   添加UnloadContent代码段:

(Code Snippet – Game Development with XNA – Gameplay Screen Unload method)

C#

public override void UnloadContent()

{

    particles = null;

 

    base.UnloadContent();

}

 

13.   重写基类Update功能：

Note: 我们将在做游戏逻辑的时候再来修改他。

(Code Snippet – Game Development with XNA – Gameplay Screen Update method)

C#

/// <summary>

/// Runs one frame of update for the game.

/// </summary>

/// <param name="gameTime">Provides a snapshot of timing values.</param>

public override void Update(GameTime gameTime,

bool otherScreenHasFocus, bool coveredByOtherScreen)

{

   float elapsed =  (float)gameTime.ElapsedGameTime.TotalSeconds;

 

   base.Update(gameTime, otherScreenHasFocus,    coveredByOtherScreen);

}

 

14.   重写基类绘图功能，当下的“游戏世界”是每秒30次。

(Code Snippet – Game Development with XNA – Gameplay Screen Draw region)

C#

/// <summary>

/// Draw the game world, effects, and HUD

/// </summary>

/// <param name="gameTime">The elapsed time since last Draw</param>

public override void Draw(GameTime gameTime)

{

   float elapsedTime = (float)gameTime.ElapsedGameTime.TotalSeconds;

 

   ScreenManager.SpriteBatch.Begin();

 

   ScreenManager.SpriteBatch.End();

}

Note: The GameTime could be used to calculate the drawing locations of various game items.

 

15.   打开 MainMenuScreen.cs，找到 StartGameMenuEntrySelected 方法，现在是空的，我们将以下代码添加进去。 这段代码的作用是当用户点击“START GAME”按钮时，将 GameplayScreen 添加到ScreenManager：

(Code Snippet – Game Development with XNA – MainMenu Screen – GameMenuEntrySelected handler)

C#

void StartGameMenuEntrySelected(object sender, EventArgs e)

{

    ScreenManager.AddScreen(new GameplayScreen());

}

 

16.   编译并运行该应用程序。 单击"开始游戏"菜单项，可以看到主菜单从屏幕的下方滚动上来。

图2

运行效果 

Note: 现在游戏的场景你还看不到，不过不要紧，明天我们就开始了，加油！！

 

17.   停止调试并回到应用程序编辑状态。

 

在个章节，你创建了新的主游戏类，并重写了游戏基类的功能。