学习笔记29（手把手教用XNA开发WINPHONE7游戏3）

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#

publicoverridevoidUpdate(GameTimegameTime,boolotherScreenHasFocus,

boolcoveredByOtherScreen)

{

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#

publicoverridevoidDraw(GameTimegameTime)

{

SpriteBatchspriteBatch = 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).

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

spriteBatch.Begin();

// Draw Background

spriteBatch.Draw(background,newVector2(0, 0),

newColor(255, 255, 255, TransitionAlpha));

// Draw Title

spriteBatch.Draw(title,newVector2(60, 55),

newColor(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#

usingAlienGameSample;

usingMicrosoft.Xna.Framework;

usingMicrosoft.Xna.Framework.Graphics;

usingMicrosoft.Xna.Framework.Audio;

usingSystem.IO.IsolatedStorage;

usingSystem.IO;

8.从GameScreen派生：

C#

classGameplayScreen :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

//

RectangleworldBounds;

boolgameOver;

intbaseLevelKillCount;

intlevelKillCount;

floatalienSpawnTimer;

floatalienSpawnRate;

floatalienMaxAccuracy;

floatalienSpeedMin;

floatalienSpeedMax;

intalienScore;

intnextLife;

inthitStreak;

inthighScore;

Randomrandom;

//

// Rendering Members

//

Texture2Dcloud1Texture;

Texture2Dcloud2Texture;

Texture2DsunTexture;

Texture2DmoonTexture;

Texture2DgroundTexture;

Texture2DtankTexture;

Texture2DalienTexture;

Texture2Dbadguy_blue;

Texture2Dbadguy_red;

Texture2Dbadguy_green;

Texture2Dbadguy_orange;

Texture2DmountainsTexture;

Texture2DhillsTexture;

Texture2DbulletTexture;

Texture2DlaserTexture;

SpriteFontscoreFont;

SpriteFontmenuFont;

Vector2cloud1Position;

Vector2cloud2Position;

Vector2sunPosition;

// Level changes, nighttime transitions, etc

floattransitionFactor;// 0.0f == day, 1.0f == night

floattransitionRate;// > 0.0f == day to night

ParticleSystemparticles;

//

// Audio Members

//

SoundEffectalienFired;

SoundEffectalienDied;

SoundEffectplayerFired;

SoundEffectplayerDied;

//Screen dimension consts

constfloat screenHeight = 800.0f;

constfloat screenWidth = 480.0f;

constint leftOffset = 25;

constint topOffset = 50;

constint 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#

publicGameplayScreen()

{

random =newRandom();

worldBounds =newRectangle(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#

publicoverridevoidLoadContent()

{

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 =newVector2(224 - cloud1Texture.Width, 32);

cloud2Position =newVector2(64, 80);

sunPosition =newVector2(16, 16);

particles =newParticleSystem(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#

publicoverridevoidUnloadContent()

{

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>

publicoverridevoidUpdate(GameTimegameTime,

boolotherScreenHasFocus,bool coveredByOtherScreen)

{

floatelapsed = (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>

publicoverridevoidDraw(GameTimegameTime)

{

floatelapsedTime = (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#

voidStartGameMenuEntrySelected(object sender,EventArgse)

{

ScreenManager.AddScreen(newGameplayScreen());

}

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。