目前，天空绘制主要有三种方法：矩形天空、天空盒和球形天空。
(1)矩形天空使用一个与地面垂直或呈一定夹角的矩形表示天空，用接近于天空的颜色或云彩纹理贴于矩形上。这种方法简单易行，但需要不断调整视角或观察点来改变场景可视域，还会对运行效率造成一定影响。
(2)天空盒是构建一个包含场景的方盒来表示天空，然后在方盒四周和顶部贴上云彩纹理。但这种方法当视角对准两个面的边界时，能够明显看到交接痕迹。
(3)球形天空通常使用半球形网格模型来表示天空，并在半球形网格上贴上一幅云彩纹理，可以使半球形网格模型绕Y轴旋转来模拟动态效果。
半球形天空类的头文件:
#pragma once
#include <d3d9.h>
#include <d3dx9.h>
#ifndef SAFE_DELETE
#define SAFE_DELETE(p) { if(p) { delete (p); (p)=NULL; } }
#endif
#ifndef SAFE_RELEASE
#define SAFE_RELEASE(p) { if(p) { (p)->Release(); (p)=NULL; } }
#endif
//--------------------------------------------------------------------------------------
// Name: class CSkybox
// Desc: 球形地形
//--------------------------------------------------------------------------------------
class CSkybox
{
private:
LPDIRECT3DDEVICE9 m_pd3dDevice;
LPDIRECT3DTEXTURE9 m_pTexture;
LPDIRECT3DINDEXBUFFER9 m_pIndexBuf;
LPDIRECT3DVERTEXBUFFER9 m_pVertexBuf;
INT m_nNumLatitudes;
INT m_nNumLongitudes;
INT m_nVertsPerLati;
INT m_nVertsPerLongi;
INT m_nNumVertices; // 顶点数
FLOAT m_fSkyboxRadius; // 半径
struct SKYBOXVERTEX
{
FLOAT _x, _y, _z;
FLOAT _u, _v;
SKYBOXVERTEX(FLOAT x, FLOAT y, FLOAT z, FLOAT u, FLOAT v)
: _x(x), _y(y), _z(z), _u(u), _v(v) {}
static const DWORD FVF = D3DFVF_XYZ | D3DFVF_TEX1;
};
public:
CSkybox(IDirect3DDevice9 *pd3dDevice);
virtual ~CSkybox(void);
public:
BOOL LoadSkybox(LPCSTR pTextureFile);
BOOL InitSkybox(INT nAlpha, INT nBeta, FLOAT nRadius);
BOOL DrawSkybox(D3DXMATRIX *pMatWorld, bool bDrawFrame=0);
};
半球形天空类的实现文件:
#pragma once
#include <d3d9.h>
#include <d3dx9.h>
#ifndef SAFE_DELETE
#define SAFE_DELETE(p) { if(p) { delete (p); (p)=NULL; } }
#endif
#ifndef SAFE_RELEASE
#define SAFE_RELEASE(p) { if(p) { (p)->Release(); (p)=NULL; } }
#endif
//--------------------------------------------------------------------------------------
// Name: class CSkybox
// Desc: 球形地形
//--------------------------------------------------------------------------------------
class CSkybox
{
private:
LPDIRECT3DDEVICE9 m_pd3dDevice;
LPDIRECT3DTEXTURE9 m_pTexture;
LPDIRECT3DINDEXBUFFER9 m_pIndexBuf;
LPDIRECT3DVERTEXBUFFER9 m_pVertexBuf;
INT m_nNumLatitudes;
INT m_nNumLongitudes;
INT m_nVertsPerLati;
INT m_nVertsPerLongi;
INT m_nNumVertices; // 顶点数
FLOAT m_fSkyboxRadius; // 半径
struct SKYBOXVERTEX
{
FLOAT _x, _y, _z;
FLOAT _u, _v;
SKYBOXVERTEX(FLOAT x, FLOAT y, FLOAT z, FLOAT u, FLOAT v)
: _x(x), _y(y), _z(z), _u(u), _v(v) {}
static const DWORD FVF = D3DFVF_XYZ | D3DFVF_TEX1;
};
public:
CSkybox(IDirect3DDevice9 *pd3dDevice);
virtual ~CSkybox(void);
public:
BOOL LoadSkybox(LPCSTR pTextureFile);
BOOL InitSkybox(INT nAlpha, INT nBeta, FLOAT nRadius);
BOOL DrawSkybox(D3DXMATRIX *pMatWorld, bool bDrawFrame=0);
};
#include "Skybox.h"
CSkybox::CSkybox(IDirect3DDevice9 *pd3dDevice)
{
m_pd3dDevice = pd3dDevice;
m_pTexture = NULL;
m_pIndexBuf = NULL;
m_pVertexBuf = NULL;
m_nNumVertices = 0;
m_nNumLatitudes = 0;
m_nNumLongitudes = 0;
m_nVertsPerLongi = 0;
m_nVertsPerLati = 0;
m_fSkyboxRadius = 0;
}
CSkybox::~CSkybox(void)
{
SAFE_RELEASE(m_pTexture);
SAFE_RELEASE(m_pIndexBuf);
SAFE_RELEASE(m_pVertexBuf);
}
BOOL CSkybox::LoadSkybox(LPCSTR pTextureFile)
{
// 加载天空纹理
if (FAILED(D3DXCreateTextureFromFile(m_pd3dDevice, pTextureFile, &m_pTexture)))
return FALSE;
return TRUE;
}
BOOL CSkybox::InitSkybox(INT nAlpha, INT nBeta, FLOAT fRadius)
{
m_fSkyboxRadius = fRadius; // 半球体的半径
m_nNumLatitudes = 360 / nAlpha; // 维度线的条数
m_nNumLongitudes = 90 / nBeta; // 经度线的条数
m_nVertsPerLongi = m_nNumLatitudes + 1; // 每条经度线上的顶点数
m_nVertsPerLati = m_nNumLongitudes + 1; // 每条维度线上的顶点数
m_nNumVertices = m_nVertsPerLati * m_nVertsPerLongi;
// 计算天空的灵活顶点
if (FAILED(m_pd3dDevice->CreateVertexBuffer(m_nNumVertices * sizeof(SKYBOXVERTEX),
D3DUSAGE_WRITEONLY, SKYBOXVERTEX::FVF, D3DPOOL_MANAGED, &m_pVertexBuf, 0)))
return FALSE;
SKYBOXVERTEX *pVertices = NULL;
m_pVertexBuf->Lock(0, 0, (void**)&pVertices, 0);
int nIndex = 0;
FLOAT fAlpha = 2.0f * D3DX_PI * nAlpha / 360.0f; // 经度角转换为弧度表示
FLOAT fBeta = 2.0f * D3DX_PI * nBeta / 360.0f; // 维度角转换为弧度表示
for (int row = 0; row < m_nNumLongitudes+1; row++)
{
for (int col = 0; col < m_nNumLatitudes+1; col++)
{
// 计算顶点的坐标
pVertices[nIndex]._x = fRadius * cosf(row * fBeta) * cosf(col * fAlpha);
pVertices[nIndex]._y = fRadius * sinf(row * fBeta);
pVertices[nIndex]._z = fRadius * cosf(row * fBeta) * sinf(col * fAlpha);
// 计算顶点的纹理坐标
pVertices[nIndex]._u = col * fAlpha / (2.0f * D3DX_PI);
pVertices[nIndex]._v = row * fBeta / (D3DX_PI / 2.0f);
nIndex++;
}
}
m_pVertexBuf->Unlock();
// 计算天空的顶点索引
if (FAILED(m_pd3dDevice->CreateIndexBuffer(m_nNumVertices * 6 *sizeof(WORD),
D3DUSAGE_WRITEONLY, D3DFMT_INDEX16, D3DPOOL_MANAGED, &m_pIndexBuf, 0)))
return FALSE;
WORD* pIndices = NULL;
m_pIndexBuf->Lock(0, 0, (void**)&pIndices, 0);
nIndex = 0;
for (int row = 0; row < m_nNumLongitudes; row++)
{
for (int col = 0; col < m_nNumLatitudes; col++)
{
pIndices[nIndex+0] = row * m_nVertsPerLongi + col;
pIndices[nIndex+1] = (row+1) * m_nVertsPerLongi + col;
pIndices[nIndex+2] = (row+1) * m_nVertsPerLongi + col + 1;
pIndices[nIndex+3] = row * m_nVertsPerLongi + col;
pIndices[nIndex+4] = (row+1) * m_nVertsPerLongi + col + 1;
pIndices[nIndex+5] = row * m_nVertsPerLongi + col + 1;
nIndex += 6;
}
}
m_pIndexBuf->Unlock();
return TRUE;
}
BOOL CSkybox::DrawSkybox(D3DXMATRIX *pMatWorld, bool bDrawFrame)
{
//纹理模式渲染
m_pd3dDevice->SetStreamSource(0, m_pVertexBuf, 0, sizeof(SKYBOXVERTEX));
m_pd3dDevice->SetFVF(SKYBOXVERTEX::FVF);
m_pd3dDevice->SetIndices(m_pIndexBuf);
m_pd3dDevice->SetTexture(0, m_pTexture);
m_pd3dDevice->SetTransform(D3DTS_WORLD, pMatWorld);
m_pd3dDevice->SetRenderState(D3DRS_LIGHTING, FALSE);
m_pd3dDevice->SetRenderState(D3DRS_CULLMODE, D3DCULL_CW);
m_pd3dDevice->DrawIndexedPrimitive(D3DPT_TRIANGLELIST, 0, 0,
m_nNumVertices, 0, m_nNumVertices * 2);
m_pd3dDevice->SetTexture(0, 0);
m_pd3dDevice->SetRenderState(D3DRS_LIGHTING, TRUE);
m_pd3dDevice->SetRenderState(D3DRS_CULLMODE, D3DCULL_CCW);
//网格模式渲染
if (bDrawFrame)
{
m_pd3dDevice->SetRenderState(D3DRS_FILLMODE, D3DFILL_WIREFRAME);
m_pd3dDevice->DrawIndexedPrimitive(D3DPT_TRIANGLELIST, 0, 0,
m_nNumVertices, 0, m_nNumVertices * 2);
m_pd3dDevice->SetRenderState(D3DRS_FILLMODE, D3DFILL_SOLID);
}
return TRUE;
}
半形天空体的演示C#实现代码如下：
using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using Microsoft.DirectX;
using Microsoft.DirectX.Direct3D;
using Microsoft.DirectX.DirectInput;
namespace TerrainVIS
{
class DomeSky
{
public IndexBuffer m_pIB;
private int[] indices; //索引缓冲区的大小为。三角形总数：(Columns)X(Rows)X2，每个三角形需要3个顶点索引值。
public VertexBuffer m_pVB;
public Texture m_pTex;
public float m_Radius=1f; //定义球形天空的半径
int MaxLatitude = 90;
//int MaxLatitude = 180;
int MinLatitude = 0;
int MaxLongitude = 360;
int MinLongitude = 0;
int LaInterval = 6;
int LongInterval =6;
int Rows = 1;//划分的格网行数，代表高度。//真正的顶点的行数和列数比网格的行数和列数均大1。
int Columns = 1;//划分的格网列数，代表宽度。
int TotalVertexes=1;
public int GetTotalVertexes()
{
this.Columns = (this.MaxLongitude - this.MinLongitude) / this.LongInterval;//在经度上分割得到格网的列数
this.Rows = (this.MaxLatitude - this.MinLatitude) / this.LaInterval;//在纬度上分割得到格网的行数
return (this.Rows + 1) * (this.Columns + 1);//真正的顶点的行数和列数比网格的行数和列数均大1。
}
/// <summary>
/// 构造函数应该完成成员变量初始化和内存空间申请的任务
/// </summary>
/// <param name="pDevice"></param>
/// <param name="L"></param>
public DomeSky(Microsoft.DirectX.Direct3D.Device pDevice,float L)
{
this.m_pTex = null;
this.m_Radius = L;
this.LaInterval = 6;
this.LongInterval = 6;
this.TotalVertexes=GetTotalVertexes();//为了完成首尾对接需要申请
this.m_pVB = new VertexBuffer(typeof(CustomVertex.PositionTextured), this.TotalVertexes, pDevice, Usage.Dynamic | Usage.WriteOnly, CustomVertex.PositionTextured.Format, Pool.Default);
this.m_pIB = new IndexBuffer(typeof(int), (this.Columns ) * (this.Rows ) * 6, pDevice, Usage.WriteOnly, Pool.Default);
this.indices = new int[(this.Columns ) * (this.Rows ) * 6];//申请指定大小的索引缓冲区
}
public void Create(Microsoft.DirectX.Direct3D.Device pDevice)
{
#region 定义顶点数组
CustomVertex.PositionTextured[] verts = new CustomVertex.PositionTextured[this.TotalVertexes];
int i = 0, j=0, index=0;
for (int a = 0; a <= this.MaxLongitude; a += this.LongInterval)//经度
{
i = a / this.LongInterval;//用来遍历列
for (int b = 0; b <= this.MaxLatitude; b += this.LaInterval)//纬度
{
//把球面坐标转化成空间直角坐标，设置球半径为2，竖直角从天顶到天底为0~90度，水平角0~360度
j = b / this.LaInterval;//用来遍历行
index = i * this.Rows + j;
verts[index] = new CustomVertex.PositionTextured();
verts[index].X = Convert.ToSingle(this.m_Radius * Math.Sin((float)b / 180.0 * Math.PI) * Math.Cos((float)a / 180.0 * Math.PI));
verts[index].Y = Convert.ToSingle(this.m_Radius * Math.Sin((float)b / 180.0 * Math.PI) * Math.Sin((float)a / 180.0 * Math.PI));
verts[index].Z = Convert.ToSingle(this.m_Radius * Math.Cos((float)b / 180.0 * Math.PI));
//计算纹理坐标的方法一
//verts[index].Tu = (float)(a / this.LongInterval) / this.Columns;
//verts[index].Tv = (float)(b / this.LaInterval) / this.Rows;
//计算纹理坐标的方法一
verts[index].Tu = (float)a / this.MaxLongitude;//单位用度或者弧度做比值结果都一样
verts[index].Tv = (float)b / this.MaxLatitude;
if (i <= this.Columns - 1 && j <= this.Rows - 1)//从最后一行或者一列格网的前一个顶点即可索引下一个顶点，故次数限定范围。
{
this.indices[index * 6 + 0] = i * this.Rows + j;
this.indices[index * 6 + 1] = (i + 1) * this.Rows + j;
this.indices[index * 6 + 2] = i * this.Rows + (j + 1);
this.indices[index * 6 + 3] = i * this.Rows + (j + 1);
this.indices[index * 6 + 4] = (i + 1) * this.Rows + j;
this.indices[index * 6 + 5] = (i + 1) * this.Rows + (j + 1);
}
}
}
#endregion
m_pVB.SetData(verts, 0, LockFlags.None);//设置顶点缓冲区的顶点数据为上面申请的顶点的数组中包含的数据
m_pTex = TextureLoader.FromFile(pDevice, "DomeSky.jpg");
m_pIB.SetData(this.indices, 0, LockFlags.None);
}
public void Render(Microsoft.DirectX.Direct3D.Device pDevice)
{
pDevice.VertexFormat = CustomVertex.PositionTextured.Format;
pDevice.SetStreamSource(0, m_pVB, 0);
pDevice.Indices = m_pIB;
pDevice.SetTexture(0, m_pTex);
//绘制半透明状态
pDevice.SetRenderState(RenderStates.AlphaBlendEnable, true);
pDevice.SetRenderState(RenderStates.BlendOperation, true);
pDevice.SetRenderState(RenderStates.SourceBlend, Blend.SourceAlpha.GetHashCode());
pDevice.SetRenderState(RenderStates.DestinationBlend, Blend.InvSourceAlpha.GetHashCode());
//下面的代码用于多层纹理映射。在此不起作用。
//pDevice.SetTextureStageState(0, TextureStageStates.AlphaOperation, TextureOperation.Modulate.GetHashCode());
//pDevice.SetTextureStageState(0, TextureStageStates.ColorArgument1, TextureArgument.Diffuse.GetHashCode());
pDevice.SetTextureStageState(0, TextureStageStates.AlphaOperation, TextureOperation.SelectArg1.GetHashCode());
pDevice.SetTextureStageState(0, TextureStageStates.AlphaArgument1, TextureArgument.TextureColor.GetHashCode());
pDevice.SetRenderState(RenderStates.MultisampleAntiAlias, true);//启用多重采样，反锯齿。
//需要调用带索引的图元绘制函数
pDevice.DrawIndexedPrimitives(PrimitiveType.TriangleList, 0, 0, (this.Rows + 1) * (this.Columns + 1), 0, indices.Length / 3);
//绘制完毕应将及时关闭Alpha混合状态
//pDevice.SetRenderState(RenderStates.AlphaBlendEnable, false);
}
public void Destroy()
{
if (m_pVB != null)
{
m_pVB.Dispose();
}
for (int i = 0; i < 5; i++)
{
if (m_pTex!= null)
{
m_pTex.Dispose();
}
}
}
}
}