在現實生活中，除了顏色以外，最重要的其實是光照，有了光照，才有了明暗、著色、高光等效果，在繼上節的紋理之后，這節來為場景加入光照效果。 在XNA中，可以簡單地把光照分為兩種，一種是環境光，一種是有向光。 環境光是不來自任何特殊方向的光，它有光源，但是被周圍環境的多次反射變得沒有確定的方向，物體各表面都均等受光。在使用時主要用環境光改變場景的基本光線顏色。 有向光是來自某個方向被物體表面反射的光，比如射燈的光等。在描述這種光線時，除了描述方向以外，還要描述散射光的顏色和物體表面高光區的顏色等其他屬性。 在使用光線的時候，還有一個額外的參數需要指定，那就是法線方向。不妨作這樣的思考，對于任意一個平面，渲染引擎是如何計算入射光和反射光的夾角呢？是如何確定該平面哪個方向為正方向的呢？其實，這些問題的答案就是依靠法線。 回顧一下法線的定義，簡單的說就是垂直于平面的垂線，對于曲面來說，就是垂直于曲面某點切線的線。法線在3D空間的重要作用就是確定面的正方向，通常定義由內部指向外部的方向為正方向，有了這個方向，渲染引擎在做光線運算和紋理貼圖時才能正確處理方向，從而達到預期的效果。 在場景中如果需要光照效果，就不能簡單的用VertexPositionTexture類了，XNA提供了VertexPositionNormalTexture類，這個類提供了對法線的表示方法。下面，我們在前面的三角形定義的基礎上，改用這個新的類，代碼如下： ~~~ ??????????triangle = new VertexPositionNormalTexture[]{ ??????????????new VertexPositionNormalTexture(new Vector3(0, 1, 0),new Vector3(0,0,1),new Vector2(0.5f,0)), ??????????????new VertexPositionNormalTexture(new Vector3(1, -1, 0),newVector3(0,0,1), new Vector2(1,1)), ??????????????new VertexPositionNormalTexture(new Vector3(-1,-1, 0),newVector3(0,0,1), new Vector2(0,1)) ?????????? }; ~~~ 注意到每個點的法線方向都用了(0,0,1)，即全部指向z軸的正方向，從而確定了整個三角形的正方向是從手機屏幕向外指向用戶。 有了這個數據定義，就可以通過BasicEffect對象添加光照效果了。代碼如下： ~~~ ??????????basicEffect.LightingEnabled = true; ??????????basicEffect.AmbientLightColor = new Vector3(0.1f, 0.1f, 0.1f); ??????????basicEffect.DirectionalLight0.DiffuseColor = Color.Red.ToVector3(); ??????????basicEffect.DirectionalLight0.Direction = Vector3.Normalize(newVector3(-0.5f, 0.5f, -1)); ??????????basicEffect.DirectionalLight0.SpecularColor = Color.White.ToVector3(); ??????????basicEffect.DirectionalLight0.Enabled = true; ~~~ 通過LightingEnabled=true可以啟動光照效果，只有該變量的值為true，后續語句中設置的光照才會得到渲染。 AmbientLightColor指定的是環境光的顏色。 通過BasicEffect可以設置環境光、漫反射光、高光以及3個有向光的效果。在上述的代碼中，通過對DirectionalLight0的設置，就是確定了一個有向光的屬性。這些屬性中，DiffuseColor是其漫反射光的顏色，Direction是一個歸一化的三維向量，用于指定光線的方向，SpecularColor是定義高光的顏色，Enabled是啟用該有向光的效果渲染。 最終的運行結果如圖所示。光源的方向是從右下角到左上角并指向屏幕內部，因此右下角的高光效果較明顯。而且整個物體被漫反射光映成了紅色，像是被夕陽照射的一樣。  其余的光照效果需要在實踐中不斷的積累，相信有了上述的學習，在運用時能夠達到目標效果。 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; VertexPositionNormalTexture[] triangle; Matrix translateMatrix=Matrix.Identity; Matrix scaleMatrix = Matrix.Identity; 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 VertexPositionNormalTexture[]{ new VertexPositionNormalTexture(new Vector3(0, 1, 0),new Vector3(0,0,1), new Vector2(0.5f,0)), new VertexPositionNormalTexture(new Vector3(1, -1, 0),new Vector3(0,0,1), new Vector2(1,1)), new VertexPositionNormalTexture(new Vector3(-1,-1, 0),new Vector3(0,0,1), new Vector2(0,1)) }; texture = Content.Load<Texture2D>(@"Tulips"); } /// <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; basicEffect.LightingEnabled = true; basicEffect.AmbientLightColor = new Vector3(0.1f, 0.1f, 0.1f); basicEffect.DirectionalLight0.DiffuseColor = Color.Red.ToVector3(); basicEffect.DirectionalLight0.Direction = Vector3.Normalize(new Vector3(-0.5f, 0.5f, -1)); basicEffect.DirectionalLight0.SpecularColor = Color.White.ToVector3(); basicEffect.DirectionalLight0.Enabled = true; foreach (EffectPass pass in basicEffect.CurrentTechnique.Passes) { pass.Apply(); GraphicsDevice.DrawUserPrimitives<VertexPositionNormalTexture>(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) ——