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)

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)

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 )

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：

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)

// 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)

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)

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)

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)

/// <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)

/// <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)

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。

转载于:https://www.cnblogs.com/zouyuntao/archive/2010/11/10/1874267.html

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