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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