在Windows Phone中進行3D開發之七紋理

       經過前幾節內容的學習，我們已經讓物體具有了平移、縮放、旋轉的三大運動能力，通過組合使用，可以形成複雜的物體運動模型。

       接下來，我們要給物體增加些顏色了，改變灰濛濛的世界。

       還記得我們之前定義的三角形資料嗎？當初定義的時候是這樣的：

           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)

            };

       我們使用了VertexPositionColor對象數組，該類型使用座標和顏色值來表示一個頂點，但在此之前，該顏色值一直沒起到作用，我們看到的都是白色的三角形，其實想讓顏色生效非常簡單，只要在Draw()方法添加下句即可：

         basicEffect.VertexColorEnabled= true;

       運行一下，絢麗的三角形就出來了。

       不過，僅用顏色顯然不能製作更逼真的物體，比如說木頭的三角形，用顏色就不能準確表達了。這時，我們需要的是使用紋理，即使用木紋的圖片貼到三角形上，最終看上去成為想要的效果。

       在Windows Phone中，紋理是使用Texture2D類來表示的，最常用的就是代表資源中的一張圖片。具體的實現是在Content工程中添加一張圖片，比如在HelloContent中添加一張wood.jpg圖片，然後在LoadContent()方法中就可以使用如下語句將圖片表示為Texture2D對象了。

        texture =Content.Load<Texture2D>(@"wood");

       有了紋理，還要有正確的貼圖座標，這裡我們稱為UV座標，一個紋理圖片的UV座標規定為：

 

        這樣我們就可以指定不同頂點的貼圖位置了。比如我們的三角形最上邊的點的UV座標就是(0.5,0)，左下角點是(0,1)，右下角點是(1,1)。對於需要使用紋理座標的三角形，前文用到的VertexPositionColor類型已經不夠了，我們需要使用VertexPositionTexture類型，即每個頂點使用座標和紋理座標來描述，而不再是座標和顏色來描述了。對應的三角形資料如下：

            triangle = newVertexPositionTexture[]{

                new VertexPositionTexture(newVector3(0, 1, 0), new Vector2(0.5f,0)),

                new VertexPositionTexture(newVector3(1, -1, 0), new Vector2(1,1)),

                new VertexPositionTexture(newVector3(-1,-1, 0), new Vector2(0,1))

            };

        最後，要想得到渲染結果，修改Draw()方法，調整basicEffect的紋理屬性為：

            basicEffect.TextureEnabled = true;

            basicEffect.Texture = texture;

        運行程式，可以得到帶木紋的三角形了。

    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;        VertexPositionTexture[] triangle;        Matrix translateMatrix=Matrix.Identity;        Matrix scaleMatrix = Matrix.CreateScale(0.5f);        Matrix rotateMatrix = Matrix.Identity;        Texture2D texture;        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 VertexPositionTexture[]{                new VertexPositionTexture(new Vector3(0, 1, 0), new Vector2(0.5f,0)),                new VertexPositionTexture(new Vector3(1, -1, 0), new Vector2(1,1)),                new VertexPositionTexture(new Vector3(-1,-1, 0), new Vector2(0,1))            };            texture = Content.Load<Texture2D>(@"wood");        }        /// <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;            basicEffect.TextureEnabled = true;            basicEffect.Texture = texture;            GraphicsDevice.SamplerStates[0] = SamplerState.PointClamp;                        foreach (EffectPass pass in basicEffect.CurrentTechnique.Passes)            {                pass.Apply();                GraphicsDevice.DrawUserPrimitives<VertexPositionTexture>(PrimitiveType.TriangleStrip, triangle, 0, 1);            }            base.Draw(gameTime);        }    }

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