在Windows Phone中进行3D开发之三空间
经过前两节的学习，我们已经具备了创建三维空间的条件了，相信很多人已经跃跃欲试了，接下来，我们就动手开始在Windows Phone中的3D开发之旅。
打开Visual Studio 2010（什么？还没有Windows Phone的开发环境？唉，自己处理一下吧，有问题问百度），新建一个项目（File->New->Project），在弹出的对话框中选择XNA Game Studio 4.0中的Windows Phone Game，在Name中就命名为“Hello”吧，点击“OK”确定。界面如下图所示。
在Solution Explorer窗口中右击项目名，执行Add->Class菜单项，如下图所示。
在弹出的对话框中按下图选择，将类命名为Camera，点击“Add”按钮。
为Camera类添加两个属性：
public Matrix view{get;protected set;}
public Matrix projection { get; protectedset; }
修改Camera类的构造函数为：
public Camera(Game game, Vector3 pos,Vector3 target, Vector3 up, float fieldOfView, float aspectRatio, floatnearPlaneDistance,float farPlaneDistance)
: base(game)
{
view = Matrix.CreateLookAt(pos,target, up);
projection =Matrix.CreatePerspectiveFieldOfView(fieldOfView,aspectRatio,nearPlaneDistance,farPlaneDistance);
}
该类的完整代码见《在Windows Phone中进行3D开发之二摄像机》一文。
打开Game1类，添加如下成员变量：
Camera camera;
Matrix world = Matrix.Identity;
BasicEffect basicEffect;
在Game1()构造方法中添加代码：
graphics.IsFullScreen =true;
在LoacContent()方法中添加代码：
camera = new Camera(this, newVector3(0, 0, 5), Vector3.Zero, Vector3.Up, MathHelper.PiOver4,GraphicsDevice.Viewport.AspectRatio, 1.0f, 50.0f);
Components.Add(camera);
basicEffect = newBasicEffect(GraphicsDevice);
这段代码中，MathHelper是一个数学上的辅助类，其PiOver4属性是π/4，即45度角。Viewport.AspectRatio是长宽比。
在Draw()方法中添加代码：
basicEffect.World = world;
basicEffect.View = camera.view;
basicEffect.Projection =camera.projection;
foreach (EffectPass pass inbasicEffect.CurrentTechnique.Passes)
{
pass.Apply();
}
BasicEffect类的作用是控制渲染效果，在3D开发中必不可少。通常用在Draw()方法中进行设置以改变渲染器的行为，后文中我们还将用它控制颜色、光线等很多特效。在前几节内容中用的较多的就是BasicEffect的三个属性，即代码中的World、View、Projection，分别代表世界矩阵、摄像机矩阵、投影矩阵。这里我们要在坐标原点绘制对象，所以World设置了单位矩阵，即Mathix.Identity。
BasicEffect里包含一些Technique，每个Technique又由若干EffectPass组成，我们要在每个EffectPass上进行Apply请求，才能在该EffectPass上进行绘制。这个Apply()方法的调用就像我们进行2D时调用SpriteBatch.Begin()一样，是绘制开始前必须调用的方法。因此在使用BasicEffect时，需要一个foreach循环。
完整的Game1类代码如下：
using System; using System.Collections.Generic; using System.Linq; using Microsoft.Xna.Framework; using Microsoft.Xna.Framework.Audio; using Microsoft.Xna.Framework.Content; using Microsoft.Xna.Framework.GamerServices; using Microsoft.Xna.Framework.Graphics; using Microsoft.Xna.Framework.Input; using Microsoft.Xna.Framework.Input.Touch; using Microsoft.Xna.Framework.Media; namespace Hello { /// <summary> /// This is the main type for your game /// </summary> public class Game1 : Microsoft.Xna.Framework.Game { GraphicsDeviceManager graphics; Camera camera; Matrix world = Matrix.Identity; BasicEffect basicEffect; public Game1() { graphics = new GraphicsDeviceManager(this); Content.RootDirectory = "Content"; // Frame rate is 30 fps by default for Windows Phone. TargetElapsedTime = TimeSpan.FromTicks(333333); // Extend battery life under lock. InactiveSleepTime = TimeSpan.FromSeconds(1); graphics.IsFullScreen = true; } /// <summary> /// Allows the game to perform any initialization it needs to before starting to run. /// This is where it can query for any required services and load any non-graphic /// related content. Calling base.Initialize will enumerate through any components /// and initialize them as well. /// </summary> protected override void Initialize() { // TODO: Add your initialization logic here base.Initialize(); } /// <summary> /// LoadContent will be called once per game and is the place to load /// all of your content. /// </summary> protected override void LoadContent() { camera = new Camera(this, new Vector3(0, 0, 5), Vector3.Zero, Vector3.Up, MathHelper.PiOver4, GraphicsDevice.Viewport.AspectRatio, 1.0f, 50.0f); Components.Add(camera); basicEffect = new BasicEffect(GraphicsDevice); } /// <summary> /// UnloadContent will be called once per game and is the place to unload /// all content. /// </summary> protected override void UnloadContent() { // TODO: Unload any non ContentManager content here } /// <summary> /// Allows the game to run logic such as updating the world, /// checking for collisions, gathering input, and playing audio. /// </summary> /// <param name="gameTime">Provides a snapshot of timing values.</param> protected override void Update(GameTime gameTime) { // Allows the game to exit if (GamePad.GetState(PlayerIndex.One).Buttons.Back == ButtonState.Pressed) this.Exit(); // TODO: Add your update logic here base.Update(gameTime); } /// <summary> /// This is called when the game should draw itself. /// </summary> /// <param name="gameTime">Provides a snapshot of timing values.</param> protected override void Draw(GameTime gameTime) { GraphicsDevice.Clear(Color.CornflowerBlue); basicEffect.World = world; basicEffect.View = camera.view; basicEffect.Projection = camera.projection; foreach (EffectPass pass in basicEffect.CurrentTechnique.Passes) { pass.Apply(); } base.Draw(gameTime); } } }
运行程序，打开模拟器，运行结果如下图所示。
不用怀疑，虽然屏幕上什么都没有，但事实上屏幕上所表现的已经是一个三维空间，我们有一个摄像机位于(0,0,5)位置，也就是屏幕外，摄像机方向指向了原点，使用了45度视角和屏幕的宽高比进行成像，近平面是1，远平面是50。在下节中，我们就将在其中加入物体。
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