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。
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：
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 上午8:14:08 阅读次数：14054
