3D系列4.6 天空球

在开始绘制水面前,让我们首先绘制一些水面上反射的东西。我们已经有了一个漂亮的地形,现在需要在黑色天空中添加一些东西。我们已经在系列2中使用了一个天空盒,它工作得非常好。但是,下面的章节我们要创建云贴图。但使用云贴图覆盖天空盒几乎是不可能的,这样的话六个面之间的边界就会可见,云贴图在边界上会终止,导致我们可以看到地形周围的盒子。

解决方法是使用天空球,它是一个包围地形的球,所以只需要一张纹理覆盖在球面上。但有个计算量很大的工作:计算正确的纹理坐标。墨卡托(译者注:Gerardus Mercator (1512-1594) –是法兰德斯的地理学家、数学家和地图绘制员,他于1538年绘制了他的第一幅世界地图。第一张以他的名字命名的投影地图出现于1569年,它比其他航海用的世界投影地图更受欢迎。) 用了几乎一生的时间解决这个复杂的问题,所以我想这已经超出了本章的范围了。

我使用天空球解决这个问题:它是球的顶部。我已经创建了一个叫做dome.x的模型,下图是模型的框架。

天空球模型

我们只需简单地将天空纹理放置在球顶部。所以添加以下变量:

Texture2D cloudMap; 
Model skyDome; 

注意我们没有使用纹理数组,因为模型只有一张纹理。在LoadContent方法中加载模型:

skyDome = Content.Load<Model> ("dome"); 
skyDome.Meshes[0].MeshParts[0].Effect = effect.Clone(device); 

我们从文件加载模型,使用自己的effect替换模型自带的。

还要在LoadTextures方法中加载天空纹理:

cloudMap = Content.Load<Texture2D> ("cloudMap"); 

让我们看一下Draw方法。我创建了一个新方法用来绘制天空球,它就是一个标准的带纹理的模型的绘制过程。制作模型时的大小为-1到+1,所以需要放大100倍避免近裁平面出现问题。

这里我们使用了和天空盒一样的两个技巧:我们需要重新根据相机位置定位天空球,我们需要关闭Z缓冲的写入。 

private void DrawSkyDome(Matrix currentViewMatrix)
 {
     device.RenderState.DepthBufferWriteEnable = false;
 
     Matrix[] modelTransforms = new Matrix[skyDome.Bones.Count];
     skyDome.CopyAbsoluteBoneTransformsTo(modelTransforms);
 
     Matrix wMatrix = Matrix.CreateTranslation(0, -0.3f, 0) * Matrix.CreateScale(100) * Matrix.CreateTranslation(cameraPosition);
     foreach (ModelMesh mesh in skyDome.Meshes)
     {
         foreach (Effect currentEffect in mesh.Effects)
         {
             Matrix worldMatrix = modelTransforms[mesh.ParentBone.Index] * wMatrix;
             currentEffect.CurrentTechnique = currentEffect.Techniques["SkyDome"];
             currentEffect.Parameters["xWorld"].SetValue(worldMatrix);
             currentEffect.Parameters["xView"].SetValue(currentViewMatrix);
             currentEffect.Parameters["xProjection"].SetValue(projectionMatrix);
             currentEffect.Parameters["xTexture0"].SetValue(cloudMap);
             currentEffect.Parameters["xEnableLighting"].SetValue(false);
         }
         mesh.Draw();
     }
     device.RenderState.DepthBufferWriteEnable = true;
 }

除了将天空球放大并根据相机移动位置,我们还要将它稍微向下移动一点,这样它的边缘就在相机之下。这会确保相机视景体的最大部分也会被天空球覆盖。然后,传入天空球纹理并使用SkyDome technique进行绘制。

别忘了在Draw 方法中调用这个方法。但是,和天空盒一样,你要确保在其他对象之前绘制天空球:

DrawSkyDome(viewMatrix);

运行代码结果如下:

程序截图

下面是代码,红色为相对于上一章改动的部分:

 using System;
 using System.Collections.Generic;
 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.Net;
 using Microsoft.Xna.Framework.Storage;
 
 namespace XNAseries4
 {
     public struct VertexMultitextured
     {
         public Vector3 Position;
         public Vector3 Normal;
         public Vector4 TextureCoordinate;
         public Vector4 TexWeights;
 
         public static int SizeInBytes = (3 + 3 + 4 + 4) * sizeof(float);
         public static VertexElement[] VertexElements = new VertexElement[]
         {
             new VertexElement( 0, 0, VertexElementFormat.Vector3, VertexElementMethod.Default, VertexElementUsage.Position, 0 ),
             new VertexElement( 0, sizeof(float) * 3, VertexElementFormat.Vector3, VertexElementMethod.Default, VertexElementUsage.Normal, 0 ),
             new VertexElement( 0, sizeof(float) * 6, VertexElementFormat.Vector4, VertexElementMethod.Default, VertexElementUsage.TextureCoordinate, 0 ),
             new VertexElement( 0, sizeof(float) * 10, VertexElementFormat.Vector4, VertexElementMethod.Default, VertexElementUsage.TextureCoordinate, 1 ),
         };
     }
 
     public class Game1 : Microsoft.Xna.Framework.Game
     {
         GraphicsDeviceManager graphics;
         GraphicsDevice device;
 
         int terrainWidth;
         int terrainLength;
         float[,] heightData;
 
         VertexBuffer terrainVertexBuffer;
         IndexBuffer terrainIndexBuffer;
         VertexDeclaration terrainVertexDeclaration;
 
         Effect effect;
         Matrix viewMatrix;
         Matrix projectionMatrix;
 
         Vector3 cameraPosition = new Vector3(130, 30, -50);
         float leftrightRot = MathHelper.PiOver2;
         float updownRot = -MathHelper.Pi / 10.0f;
         const float rotationSpeed = 0.3f;
         const float moveSpeed = 30.0f;
         MouseState originalMouseState;
 
         Texture2D grassTexture;
         Texture2D sandTexture;
         Texture2D rockTexture;
         Texture2D snowTexture;
         Texture2D cloudMap;
         
         Model skyDome;
 
         public Game1()
         {
             graphics = new GraphicsDeviceManager(this);
             Content.RootDirectory = "Content";
         }
 
         protected override void Initialize()
         {
             graphics.PreferredBackBufferWidth = 500;
             graphics.PreferredBackBufferHeight = 500;
 
             graphics.ApplyChanges();
             Window.Title = "Riemer's XNA Tutorials -- Series 4";
 
             base.Initialize();
         }
 
         protected override void LoadContent()
         {
             device = GraphicsDevice;

            effect = Content.Load<Effect> ("Series4Effects");
            UpdateViewMatrix();
            projectionMatrix = Matrix.CreatePerspectiveFieldOfView(MathHelper.PiOver4, device.Viewport.AspectRatio, 0.3f, 1000.0f);

            Mouse.SetPosition(device.Viewport.Width / 2, device.Viewport.Height / 2);
            originalMouseState = Mouse.GetState();

            skyDome = Content.Load<Model> ("dome");            skyDome.Meshes[0].MeshParts[0].Effect = effect.Clone(device);
 
             LoadVertices();
             LoadTextures();
         }
 
         private void LoadVertices()
         {

            Texture2D heightMap = Content.Load<Texture2D> ("heightmap");            LoadHeightData(heightMap);

            VertexMultitextured[] terrainVertices = SetUpTerrainVertices();
            int[] terrainIndices = SetUpTerrainIndices();
            terrainVertices = CalculateNormals(terrainVertices, terrainIndices);
            CopyToTerrainBuffers(terrainVertices, terrainIndices);
            terrainVertexDeclaration = new VertexDeclaration(device, VertexMultitextured.VertexElements);
        }

        private void LoadTextures()
        {

            grassTexture = Content.Load<Texture2D> ("grass");
            sandTexture = Content.Load<Texture2D> ("sand");
            rockTexture = Content.Load<Texture2D> ("rock");
            snowTexture = Content.Load<Texture2D> ("snow");

            cloudMap = Content.Load<Texture2D> ("cloudMap");
         }
 
         private void LoadHeightData(Texture2D heightMap)
         {
             float minimumHeight = float.MaxValue;
             float maximumHeight = float.MinValue;
 
             terrainWidth = heightMap.Width;
             terrainLength = heightMap.Height;
 
             Color[] heightMapColors = new Color[terrainWidth * terrainLength];
             heightMap.GetData(heightMapColors);
 
             heightData = new float[terrainWidth, terrainLength];
             for (int x = 0; x < terrainWidth; x++)
                 for (int y = 0; y < terrainLength; y++)
                 {
                     heightData[x, y] = heightMapColors[x + y * terrainWidth].R;
                     if (heightData[x, y] < minimumHeight) minimumHeight = heightData[x, y];
                     if (heightData[x, y] > maximumHeight) maximumHeight = heightData[x, y];
                 }
 
             for (int x = 0; x < terrainWidth; x++)
                 for (int y = 0; y < terrainLength; y++)
                     heightData[x, y] = (heightData[x, y] - minimumHeight) / (maximumHeight - minimumHeight) * 30.0f;
         }
 
         private VertexMultitextured[] SetUpTerrainVertices()
         {
             VertexMultitextured[] terrainVertices = new VertexMultitextured[terrainWidth * terrainLength];
 
             for (int x = 0; x < terrainWidth; x++)
             {
                 for (int y = 0; y < terrainLength; y++)
                 {
                     terrainVertices[x + y * terrainWidth].Position = new Vector3(x, heightData[x, y], -y);
                     terrainVertices[x + y * terrainWidth].TextureCoordinate.X = (float)x / 30.0f;
                     terrainVertices[x + y * terrainWidth].TextureCoordinate.Y = (float)y / 30.0f;
 
                     terrainVertices[x + y * terrainWidth].TexWeights.X = MathHelper.Clamp(1.0f - Math.Abs(heightData[x, y] - 0) / 8.0f, 0, 1);
                     terrainVertices[x + y * terrainWidth].TexWeights.Y = MathHelper.Clamp(1.0f - Math.Abs(heightData[x, y] - 12) / 6.0f, 0, 1);
                     terrainVertices[x + y * terrainWidth].TexWeights.Z = MathHelper.Clamp(1.0f - Math.Abs(heightData[x, y] - 20) / 6.0f, 0, 1);
                     terrainVertices[x + y * terrainWidth].TexWeights.W = MathHelper.Clamp(1.0f - Math.Abs(heightData[x, y] - 30) / 6.0f, 0, 1);
 
                     float total = terrainVertices[x + y * terrainWidth].TexWeights.X;
                     total += terrainVertices[x + y * terrainWidth].TexWeights.Y;
                     total += terrainVertices[x + y * terrainWidth].TexWeights.Z;
                     total += terrainVertices[x + y * terrainWidth].TexWeights.W;
 
                     terrainVertices[x + y * terrainWidth].TexWeights.X /= total;
                     terrainVertices[x + y * terrainWidth].TexWeights.Y /= total;
                     terrainVertices[x + y * terrainWidth].TexWeights.Z /= total;
                     terrainVertices[x + y * terrainWidth].TexWeights.W /= total;
                 }
             }
 
             return terrainVertices;
         }
 
         private int[] SetUpTerrainIndices()
         {
             int[] indices = new int[(terrainWidth - 1) * (terrainLength - 1) * 6];
             int counter = 0;
             for (int y = 0; y < terrainLength - 1; y++)
             {
                 for (int x = 0; x < terrainWidth - 1; x++)
                 {
                     int lowerLeft = x + y * terrainWidth;
                     int lowerRight = (x + 1) + y * terrainWidth;
                     int topLeft = x + (y + 1) * terrainWidth;
                     int topRight = (x + 1) + (y + 1) * terrainWidth;
 
                     indices[counter++] = topLeft;
                     indices[counter++] = lowerRight;
                     indices[counter++] = lowerLeft;
 
                     indices[counter++] = topLeft;
                     indices[counter++] = topRight;
                     indices[counter++] = lowerRight;
                 }
             }
 
             return indices;
         }
 
         private VertexMultitextured[] CalculateNormals(VertexMultitextured[] vertices, int[] indices)
         {
             for (int i = 0; i < vertices.Length; i++)
                 vertices[i].Normal = new Vector3(0, 0, 0);
 
             for (int i = 0; i < indices.Length / 3; i++)
             {
                 int index1 = indices[i * 3];
                 int index2 = indices[i * 3 + 1];
                 int index3 = indices[i * 3 + 2];
 
                 Vector3 side1 = vertices[index1].Position - vertices[index3].Position;
                 Vector3 side2 = vertices[index1].Position - vertices[index2].Position;
                 Vector3 normal = Vector3.Cross(side1, side2);
 
                 vertices[index1].Normal += normal;
                 vertices[index2].Normal += normal;
                 vertices[index3].Normal += normal;
             }
 
             for (int i = 0; i < vertices.Length; i++)
                 vertices[i].Normal.Normalize();
 
             return vertices;
         }
 
         private void CopyToTerrainBuffers(VertexMultitextured[] vertices, int[] indices)
         {
             terrainVertexBuffer = new VertexBuffer(device, vertices.Length * VertexMultitextured.SizeInBytes, BufferUsage.WriteOnly);
             terrainVertexBuffer.SetData(vertices);
 
             terrainIndexBuffer = new IndexBuffer(device, typeof(int), indices.Length, BufferUsage.WriteOnly);
             terrainIndexBuffer.SetData(indices);
         }
 
         protected override void UnloadContent()
         {
         }
 
         protected override void Update(GameTime gameTime)
         {
             if (GamePad.GetState(PlayerIndex.One).Buttons.Back == ButtonState.Pressed)
                 this.Exit();
 
             float timeDifference = (float)gameTime.ElapsedGameTime.TotalMilliseconds / 1000.0f;
             ProcessInput(timeDifference);
 
             base.Update(gameTime);
         }
 
         private void ProcessInput(float amount)
         {
             MouseState currentMouseState = Mouse.GetState();
             if (currentMouseState != originalMouseState)
             {
                 float xDifference = currentMouseState.X - originalMouseState.X;
                 float yDifference = currentMouseState.Y - originalMouseState.Y;
                 leftrightRot -= rotationSpeed * xDifference * amount;
                 updownRot -= rotationSpeed * yDifference * amount;
                 Mouse.SetPosition(device.Viewport.Width / 2, device.Viewport.Height / 2);
                 UpdateViewMatrix();
             }
 
             Vector3 moveVector = new Vector3(0, 0, 0);
             KeyboardState keyState = Keyboard.GetState();
             if (keyState.IsKeyDown(Keys.Up) || keyState.IsKeyDown(Keys.W))
                 moveVector += new Vector3(0, 0, -1);
             if (keyState.IsKeyDown(Keys.Down) || keyState.IsKeyDown(Keys.S))
                 moveVector += new Vector3(0, 0, 1);
             if (keyState.IsKeyDown(Keys.Right) || keyState.IsKeyDown(Keys.D))
                 moveVector += new Vector3(1, 0, 0);
             if (keyState.IsKeyDown(Keys.Left) || keyState.IsKeyDown(Keys.A))
                 moveVector += new Vector3(-1, 0, 0);
             if (keyState.IsKeyDown(Keys.Q))
                 moveVector += new Vector3(0, 1, 0);
             if (keyState.IsKeyDown(Keys.Z))
                 moveVector += new Vector3(0, -1, 0);
             AddToCameraPosition(moveVector * amount);
         }
 
         private void AddToCameraPosition(Vector3 vectorToAdd)
         {
             Matrix cameraRotation = Matrix.CreateRotationX(updownRot) * Matrix.CreateRotationY(leftrightRot);
             Vector3 rotatedVector = Vector3.Transform(vectorToAdd, cameraRotation);
             cameraPosition += moveSpeed * rotatedVector;
             UpdateViewMatrix();
         }
 
         private void UpdateViewMatrix()
         {
             Matrix cameraRotation = Matrix.CreateRotationX(updownRot) * Matrix.CreateRotationY(leftrightRot);
 
             Vector3 cameraOriginalTarget = new Vector3(0, 0, -1);
             Vector3 cameraOriginalUpVector = new Vector3(0, 1, 0);
 
             Vector3 cameraRotatedTarget = Vector3.Transform(cameraOriginalTarget, cameraRotation);
             Vector3 cameraFinalTarget = cameraPosition + cameraRotatedTarget;
 
             Vector3 cameraRotatedUpVector = Vector3.Transform(cameraOriginalUpVector, cameraRotation);
 
             viewMatrix = Matrix.CreateLookAt(cameraPosition, cameraFinalTarget, cameraRotatedUpVector);
         }
 
         protected override void Draw(GameTime gameTime)
         {
             float time = (float)gameTime.TotalGameTime.TotalMilliseconds / 100.0f;
             device.RenderState.CullMode = CullMode.None;
 
             device.Clear(ClearOptions.Target | ClearOptions.DepthBuffer, Color.Black, 1.0f, 0);
             DrawSkyDome(viewMatrix);
             DrawTerrain(viewMatrix);            
 
             base.Draw(gameTime);
         }
 
         private void DrawTerrain(Matrix currentViewMatrix)
         {
             effect.CurrentTechnique = effect.Techniques["MultiTextured"];
             effect.Parameters["xTexture0"].SetValue(sandTexture);
             effect.Parameters["xTexture1"].SetValue(grassTexture);
             effect.Parameters["xTexture2"].SetValue(rockTexture);
             effect.Parameters["xTexture3"].SetValue(snowTexture);
 
             Matrix worldMatrix = Matrix.Identity;
             effect.Parameters["xWorld"].SetValue(worldMatrix);
             effect.Parameters["xView"].SetValue(currentViewMatrix);
             effect.Parameters["xProjection"].SetValue(projectionMatrix);            
 
             effect.Parameters["xEnableLighting"].SetValue(true);
             effect.Parameters["xAmbient"].SetValue(0.4f);
             effect.Parameters["xLightDirection"].SetValue(new Vector3(-0.5f, -1, -0.5f));
 
             effect.Begin();
             foreach (EffectPass pass in effect.CurrentTechnique.Passes)
             {
                 pass.Begin();
 
                 device.Vertices[0].SetSource(terrainVertexBuffer, 0, VertexMultitextured.SizeInBytes);
                 device.Indices = terrainIndexBuffer;
                 device.VertexDeclaration = terrainVertexDeclaration;
 
                 int noVertices = terrainVertexBuffer.SizeInBytes / VertexMultitextured.SizeInBytes;
                 int noTriangles = terrainIndexBuffer.SizeInBytes / sizeof(int) / 3;
                 device.DrawIndexedPrimitives(PrimitiveType.TriangleList, 0, 0, noVertices, 0, noTriangles);
 
                 pass.End();
             }
             effect.End();
         }
 
         private void DrawSkyDome(Matrix currentViewMatrix)
         {
             device.RenderState.DepthBufferWriteEnable = false;
 
             Matrix[] modelTransforms = new Matrix[skyDome.Bones.Count];
             skyDome.CopyAbsoluteBoneTransformsTo(modelTransforms);
 
             Matrix wMatrix = Matrix.CreateTranslation(0, -0.3f, 0) * Matrix.CreateScale(100) * Matrix.CreateTranslation(cameraPosition);
             foreach (ModelMesh mesh in skyDome.Meshes)
             {
                 foreach (Effect currentEffect in mesh.Effects)
                 {
                     Matrix worldMatrix = modelTransforms[mesh.ParentBone.Index] * wMatrix;
                     currentEffect.CurrentTechnique = currentEffect.Techniques["Textured"];
                     currentEffect.Parameters["xWorld"].SetValue(worldMatrix);
                     currentEffect.Parameters["xView"].SetValue(currentViewMatrix);
                     currentEffect.Parameters["xProjection"].SetValue(projectionMatrix);
                     currentEffect.Parameters["xTexture"].SetValue(cloudMap);
                     currentEffect.Parameters["xEnableLighting"].SetValue(false);
                 }
                 mesh.Draw();
             }
             device.RenderState.DepthBufferWriteEnable = true;
         }
     }
 }

发布时间:2009/12/14 8:14:08  阅读次数:13430

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