上節內容中，我們讓物體擁有了最基本的平移和縮放的運動。現在我們來看三大運動之一的旋轉運動。 同上節的知識一樣，要讓物體發生旋轉，只需要在對應的坐標軸上與一個矩陣相乘。這個矩陣的構造方法有三種，分別是： Matrix ?CreateRotationX(float radians); Matrix ?CreateRotationY(floatradians); Matrix ?CreateRotationZ(float radians); 代表在x、y、z三個坐標軸上的旋轉角度，其中radians是弧度表示，如果想使用我們熟悉的角度的話，可以使用MathHelper.ToRadians(10)進行轉換。 除了沿著坐標軸旋轉以外，還有一種是采用飛行器的偏航、翻滾、俯仰表示方式進行的旋轉，使用的矩陣構造方法是： Matrix ?CreateFromYawPitchRoll(float yaw, float pitch, float roll); 有興趣的朋友可以自行學習。 還是沿用上節課我們建好的XNA項目，在VS2010中打開該項目。打開Game1.cs文件，我們來修改Game1類。為其添加成員變量，代表旋轉矩陣： Matrix ?rotateMatrix=Matrix.Identity; 同時為了便于觀察，我們將上節使用的scaleMatrix取值為0.5倍的縮放： Matrixs ?caleMatrix = Matrix.CreateScale(0.5f); 然后在Draw()方法中修改basicEffect對象的World屬性： basicEffect.World= scaleMatrix * translateMatrix * rotateMatrix; 在Update()方法中去掉對scaleMatrix的變化并增加對rotateMatrix的處理： //scaleMatrix= Matrix.CreateScale(0.9f); rotateMatrix*= Matrix.CreateRotationZ(MathHelper.ToRadians(10)); 也即每次點擊屏幕產生10度的旋轉。 運行程序，觀察旋轉的結果。然后嘗試將Draw()中的 basicEffect.World= scaleMatrix * translateMatrix * rotateMatrix; 改成 basicEffect.World= scaleMatrix * rotateMatrix * translateMatrix; 來觀察對旋轉的影響。從中可以看出，前者是先沿著物體的x轉產生了平移，然后再按平移后所在的位置的z軸進行旋轉，產生了像螺線一樣的運動。而后者是先沿z軸進行了旋轉，再沿x軸進行平移，產生了一邊向屏幕右側平移同時繞自身z軸旋轉的效果。因此，在實際項目中要小心處理矩陣運算。 另外，也可以修改代碼，觀察沿x、y軸旋轉的情況。 當我們讓三角形繞y軸旋轉的時候，會發現一個奇怪的現象，隨著物體的旋轉，當物體的背面朝向我們時，我們就看不到它了。其實這是渲染引擎的優化設置，因為對于物體的背面，實際上是不進行渲染的，也就是常說的背面消隱，有需要關注的朋友可以查找相關的資料，在這里要想取消背面消隱選項，只需要修改一下GraphicsDevice的柵格化參數，即在Draw()方法中加入下面的代碼： ~~~ ??????????GraphicsDevice.Clear(Color.CornflowerBlue); ??????????RasterizerState rasterizerState = new RasterizerState(); ??????????rasterizerState.CullMode = CullMode.None; ??????????GraphicsDevice.RasterizerState = rasterizerState; ~~~ ? ???附本節Game1類的完整源碼： ~~~ public class Game1 : Microsoft.Xna.Framework.Game { GraphicsDeviceManager graphics; Camera camera; Matrix world = Matrix.Identity; BasicEffect basicEffect; VertexPositionColor[] triangle; Matrix translateMatrix=Matrix.Identity; Matrix scaleMatrix = Matrix.CreateScale(0.5f); Matrix rotateMatrix = Matrix.Identity; 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); triangle = new VertexPositionColor[]{ new VertexPositionColor(new Vector3(0, 1, 0), Color.Red), new VertexPositionColor(new Vector3(1, -1, 0), Color.Green), new VertexPositionColor(new Vector3(-1,-1, 0), Color.Blue) }; } /// <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(); TouchPanel.EnabledGestures = GestureType.Tap; if (TouchPanel.IsGestureAvailable) { GestureSample gestureSample = TouchPanel.ReadGesture(); if (gestureSample.GestureType == GestureType.Tap) { translateMatrix *= Matrix.CreateTranslation(0.3f, 0, 0); //scaleMatrix = Matrix.CreateScale(0.9f); rotateMatrix *= Matrix.CreateRotationY(MathHelper.ToRadians(10)); } } 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); RasterizerState rasterizerState = new RasterizerState(); rasterizerState.CullMode = CullMode.None; GraphicsDevice.RasterizerState = rasterizerState; basicEffect.World = scaleMatrix * translateMatrix * rotateMatrix; basicEffect.View = camera.view; basicEffect.Projection = camera.projection; foreach (EffectPass pass in basicEffect.CurrentTechnique.Passes) { pass.Apply(); GraphicsDevice.DrawUserPrimitives<VertexPositionColor>(PrimitiveType.TriangleStrip, triangle, 0, 1); } base.Draw(gameTime); } } ~~~ ——歡迎轉載，請注明出處 [http://blog.csdn.net/caowenbin](http://blog.csdn.net/caowenbin) ——