31. D3D雾

为3D场景增加雾会得到更真实的渲染效果。雾可以增加大量真实感，尤其对地形、树林地区以及幽灵般的户外背景。同样，雾可以很好地限制观察者对环境的可见度。现实中并不存在无限的视觉距离。事实上，这就是虚拟环境的一个镜像。通过限制观察距离，同样可以限制发送给管道的多边形数目。这对于提高渲染时间更有用。如果读者还记得PS游戏机上的第一个游戏《寂静岭》(Silient Hill)，该游戏物景中有许多雾，很难看到外面的事物，除非是事物就在游戏玩家的面前，就可以很清楚地了解这一点。

       Direct3D中有两类硬件雾可用：顶点雾和像素雾。顶点雾是按照每个顶点来计算雾的数据，而像素雾根据像素级别计算雾的数据。由于通常像素比顶点要多得多，因此两者相比而言，像素雾的渲染速度较慢。同样，顶点雾提供了很好的视觉效果。有了顶点雾，就可以在表面上逐点内插处理雾的信息。

 使用雾就要使用RenderScene()函数。需要设置雾和使用雾的代码非常简短，演示程序也十分简单。

CHAPTER6文件夹中的Fog演示程序就像Antialiasing演示程序一样代码很少。在Fog演示程序中正方形充当大地，并启用雾。除了要设置雾和绘制的几何图形数据之外，Fog演示程序是第4章中Texture Mapping演示程序的改进版。如果读者想跟随本书一起学习，那么可以从Texture Mapping演示程序中提取代码，修改InitializeObjects()函数以使用雾，并修改纹理正方形的大小和方位。程序清单6.3给出了完整的InitializeObjects()函数。

bool InitializeObjects()
{
   D3DCAPS9 caps;
   g_D3DDevice->GetDeviceCaps(&caps);

   // Start and end distance of the fog.
   float start = 2, end = 8;

   // Set fog properties.
   // 设置雾的相关属性
   g_D3DDevice->SetRenderState(D3DRS_FOGENABLE, true);  // 启用雾效果

   // 设置要渲染的雾的期望颜色(这里为灰色)
   g_D3DDevice->SetRenderState(D3DRS_FOGCOLOR,
                               D3DCOLOR_XRGB(128, 128, 128));

   // 使用顶点雾
   g_D3DDevice->SetRenderState(D3DRS_FOGVERTEXMODE, D3DFOG_LINEAR);

   // 指定雾的开始距离和终点距离
   g_D3DDevice->SetRenderState(D3DRS_FOGSTART, *(DWORD*)(&start));
   g_D3DDevice->SetRenderState(D3DRS_FOGEND, *(DWORD*)(&end));

   // Pixel Fog  像素雾
   //g_D3DDevice->SetRenderState(D3DRS_FOGTABLEMODE, D3DFOG_LINEAR);

   // Can only use if hardware supports it.
   // 如果支持，则启用基于距离的雾
   if(caps.RasterCaps & D3DPRASTERCAPS_FOGRANGE)
      g_D3DDevice->SetRenderState(D3DRS_RANGEFOGENABLE, true);


   // Object
   stD3DVertex objData[] =
      {
         {-2.5f, -0.5f, -6.0f, D3DCOLOR_XRGB(255,255,255), 0.0f, 1.0f},
         {2.5f, -0.5f,  -6.0f, D3DCOLOR_XRGB(255,255,255), 1.0f, 1.0f},
          {2.5f, -0.5f, 6.0f, D3DCOLOR_XRGB(255,255,255), 1.0f, 0.0f},

          {2.5f, -0.5f, 6.0f, D3DCOLOR_XRGB(255,255,255), 1.0f, 0.0f},
         {-2.5f, -0.5f, 6.0f, D3DCOLOR_XRGB(255,255,255), 0.0f, 0.0f},
          {-2.5f, -0.5f, -6.0f, D3DCOLOR_XRGB(255,255,255), 0.0f, 1.0f}
      };

   // Create the vertex buffer.
   if(FAILED(g_D3DDevice->CreateVertexBuffer(sizeof(objData), 0,
             D3DFVF_VERTEX, D3DPOOL_DEFAULT,
             &g_VertexBuffer, NULL))) return false;
   
   // Fill the vertex buffer.
   void *ptr;
   if(FAILED(g_VertexBuffer->Lock(0, sizeof(objData),
      (void**)&ptr, 0))) return false;
   memcpy(ptr, objData, sizeof(objData));
   g_VertexBuffer->Unlock();


   // Load the texture image from file.
   if(D3DXCreateTextureFromFile(g_D3DDevice, "ground.bmp",
      &g_Texture) != D3D_OK) return false;


    // Set default rendering states.
   g_D3DDevice->SetRenderState(D3DRS_LIGHTING, FALSE);
    g_D3DDevice->SetRenderState(D3DRS_CULLMODE, D3DCULL_NONE);


   // Set the projection matrix.
   D3DXMatrixPerspectiveFovLH(&g_projection, 45.0f,
      WINDOW_WIDTH/WINDOW_HEIGHT, 0.1f, 1000.0f);

   g_D3DDevice->SetTransform(D3DTS_PROJECTION, &g_projection);


   // Define camera information.
   D3DXVECTOR3 cameraPos(0.0f, 0.0f, -3.0f);
   D3DXVECTOR3 lookAtPos(0.0f, 0.0f, 0.0f);
   D3DXVECTOR3 upDir(0.0f, 1.0f, 0.0f);

   // Build view matrix.
   D3DXMatrixLookAtLH(&g_ViewMatrix, &cameraPos,
                      &lookAtPos, &upDir);

   return true;
}

　　代码中，从InitializeObjects()函数开始，先获取设备性能。稍后将用其测试硬件是否支持D3DRS_RANGEFOGENABLE以便使用硬件雾范围。之后，通过几次调用SetRenderState()函数设置雾。第一种状态D3DRS_FOGENABLE用于在API中启用雾效果。第二种状态D3DRS_FOGCOLOR用于设置要渲染的雾的期望颜色。第三种状态D3DRS_FOGVERTEXMODE指明了正在使用顶点雾。使用像素雾将需要使用D3DRS_FOGTABLEMODE而不是D3DRS_FOGVERTEXMODE。第四种和第五种状态D3DRS_FOGSTART和D3DRS_FOGEND指定雾的开始距离和终点距离。这就会让Direct3D知道雾在观察者前面的开始距离以及最远处的终点位置。令人感兴趣的最后一行代码是最后的渲染状态D3DRS_RANGEFOGENABLE，它将启用基于距离的雾，该值在变换和光照阶段由Direct3D计算得到。基于距离的雾只能在支持它的硬件上使用，不支持它的硬件上当然就不能使用。所以本书使用设备性能来测试运行演示程序的硬件是否支持它。

完整代码：

#include <d3d9.h>
#include <d3dx9.h>

#pragma comment(lib, "d3d9.lib")
#pragma comment(lib, "d3dx9.lib")

#define WINDOW_CLASS    "UGPDX"
#define WINDOW_NAME     "Fog"
#define WINDOW_WIDTH    640
#define WINDOW_HEIGHT   480

// Function Prototypes...
bool InitializeD3D(HWND hWnd, bool fullscreen);
bool InitializeObjects();
void RenderScene();
void Shutdown();


// Direct3D object and device.
LPDIRECT3D9 g_D3D = NULL;
LPDIRECT3DDEVICE9 g_D3DDevice = NULL;

// Matrices.
D3DXMATRIX g_projection;
D3DXMATRIX g_ViewMatrix;

// Vertex buffer to hold the geometry.
LPDIRECT3DVERTEXBUFFER9 g_VertexBuffer = NULL;

// Holds a texture image.
LPDIRECT3DTEXTURE9 g_Texture = NULL;

// A structure for our custom vertex type
struct stD3DVertex
{
    float x, y, z;
    unsigned long color;
    float tu, tv;
};

// Our custom FVF, which describes our custom vertex structure
#define D3DFVF_VERTEX (D3DFVF_XYZ | D3DFVF_DIFFUSE | D3DFVF_TEX1)


LRESULT WINAPI MsgProc(HWND hWnd, UINT msg, WPARAM wParam, LPARAM lParam)
{
    switch(msg)
    {
    case WM_DESTROY:
        PostQuitMessage(0);
        return 0;
        break;

    case WM_KEYUP:
        if(wParam == VK_ESCAPE) PostQuitMessage(0);
        break;
    }

    return DefWindowProc(hWnd, msg, wParam, lParam);
}


int WINAPI WinMain(HINSTANCE hInst, HINSTANCE prevhInst, LPSTR cmdLine, int show)
{
    // Register the window class
    WNDCLASSEX wc = { sizeof(WNDCLASSEX), CS_CLASSDC, MsgProc, 0L, 0L,
        GetModuleHandle(NULL), NULL, NULL, NULL, NULL,
        WINDOW_CLASS, NULL };
    RegisterClassEx(&wc);

    // Create the application's window
    HWND hWnd = CreateWindow(WINDOW_CLASS, WINDOW_NAME, WS_OVERLAPPEDWINDOW,
        100, 100, WINDOW_WIDTH, WINDOW_HEIGHT,
        GetDesktopWindow(), NULL, wc.hInstance, NULL);

    // Initialize Direct3D
    if(InitializeD3D(hWnd, false))
    {
        // Show the window
        ShowWindow(hWnd, SW_SHOWDEFAULT);
        UpdateWindow(hWnd);

        // Enter the message loop
        MSG msg;
        ZeroMemory(&msg, sizeof(msg));

        while(msg.message != WM_QUIT)
        {
            if(PeekMessage(&msg, NULL, 0U, 0U, PM_REMOVE))
            {
                TranslateMessage(&msg);
                DispatchMessage(&msg);
            }
            else
                RenderScene();
        }
    }

    // Release any and all resources.
    Shutdown();

    // Unregister our window.
    UnregisterClass(WINDOW_CLASS, wc.hInstance);
    return 0;
}


bool InitializeD3D(HWND hWnd, bool fullscreen)
{
    D3DDISPLAYMODE displayMode;

    // Create the D3D object.
    g_D3D = Direct3DCreate9(D3D_SDK_VERSION);
    if(g_D3D == NULL) return false;

    // Get the desktop display mode.
    if(FAILED(g_D3D->GetAdapterDisplayMode(D3DADAPTER_DEFAULT, &displayMode)))
        return false;

    // Set up the structure used to create the D3DDevice
    D3DPRESENT_PARAMETERS d3dpp;
    ZeroMemory(&d3dpp, sizeof(d3dpp));

    if(fullscreen)
    {
        d3dpp.Windowed = FALSE;
        d3dpp.BackBufferWidth = WINDOW_WIDTH;
        d3dpp.BackBufferHeight = WINDOW_HEIGHT;
    }
    else
        d3dpp.Windowed = TRUE;
    d3dpp.SwapEffect = D3DSWAPEFFECT_DISCARD;
    d3dpp.BackBufferFormat = displayMode.Format;

    // Create the D3DDevice
    if(FAILED(g_D3D->CreateDevice(D3DADAPTER_DEFAULT, D3DDEVTYPE_HAL, hWnd,
        D3DCREATE_SOFTWARE_VERTEXPROCESSING, &d3dpp, &g_D3DDevice)))
    {
        return false;
    }

    // Initialize any objects we will be displaying.
    if(!InitializeObjects()) return false;

    return true;
}


bool InitializeObjects()
{
    D3DCAPS9 caps;
    g_D3DDevice->GetDeviceCaps(&caps);

    // Start and end distance of the fog.
    float start = 2, end = 8;

    // Set fog properties.
    g_D3DDevice->SetRenderState(D3DRS_FOGENABLE, true);
    g_D3DDevice->SetRenderState(D3DRS_FOGCOLOR, D3DCOLOR_XRGB(128, 128, 128));
    g_D3DDevice->SetRenderState(D3DRS_FOGVERTEXMODE, D3DFOG_LINEAR);
    g_D3DDevice->SetRenderState(D3DRS_FOGSTART, *(DWORD*)(&start));
    g_D3DDevice->SetRenderState(D3DRS_FOGEND, *(DWORD*)(&end));

    // Pixel Fog
    //g_D3DDevice->SetRenderState(D3DRS_FOGTABLEMODE, D3DFOG_LINEAR);

    // Can only use if hardware supports it.
    if(caps.RasterCaps & D3DPRASTERCAPS_FOGRANGE)
        g_D3DDevice->SetRenderState(D3DRS_RANGEFOGENABLE, true);


    // Object
    stD3DVertex objData[] =
    {
        {-2.5f, -0.5f, -6.0f, D3DCOLOR_XRGB(255,255,255), 0.0f, 1.0f},
        {2.5f, -0.5f,  -6.0f, D3DCOLOR_XRGB(255,255,255), 1.0f, 1.0f},
        {2.5f, -0.5f, 6.0f, D3DCOLOR_XRGB(255,255,255), 1.0f, 0.0f},

        {2.5f, -0.5f, 6.0f, D3DCOLOR_XRGB(255,255,255), 1.0f, 0.0f},
        {-2.5f, -0.5f, 6.0f, D3DCOLOR_XRGB(255,255,255), 0.0f, 0.0f},
        {-2.5f, -0.5f, -6.0f, D3DCOLOR_XRGB(255,255,255), 0.0f, 1.0f}
    };

    // Create the vertex buffer.
    if(FAILED(g_D3DDevice->CreateVertexBuffer(sizeof(objData), 0,
        D3DFVF_VERTEX, D3DPOOL_DEFAULT,
        &g_VertexBuffer, NULL))) return false;

    // Fill the vertex buffer.
    void *ptr;
    if(FAILED(g_VertexBuffer->Lock(0, sizeof(objData),
        (void**)&ptr, 0))) return false;
    memcpy(ptr, objData, sizeof(objData));
    g_VertexBuffer->Unlock();


    // Load the texture image from file.
    if(D3DXCreateTextureFromFile(g_D3DDevice, "ground.bmp",
        &g_Texture) != D3D_OK) return false;


    // Set default rendering states.
    g_D3DDevice->SetRenderState(D3DRS_LIGHTING, FALSE);
    g_D3DDevice->SetRenderState(D3DRS_CULLMODE, D3DCULL_NONE);


    // Set the projection matrix.
    D3DXMatrixPerspectiveFovLH(&g_projection, 45.0f,
        WINDOW_WIDTH/WINDOW_HEIGHT, 0.1f, 1000.0f);

    g_D3DDevice->SetTransform(D3DTS_PROJECTION, &g_projection);


    // Define camera information.
    D3DXVECTOR3 cameraPos(0.0f, 0.0f, -3.0f);
    D3DXVECTOR3 lookAtPos(0.0f, 0.0f, 0.0f);
    D3DXVECTOR3 upDir(0.0f, 1.0f, 0.0f);

    // Build view matrix.
    D3DXMatrixLookAtLH(&g_ViewMatrix, &cameraPos,
        &lookAtPos, &upDir);

    return true;
}


void RenderScene()
{
    // Clear the backbuffer.
    g_D3DDevice->Clear(0, NULL, D3DCLEAR_TARGET, D3DCOLOR_XRGB(128,128,128), 1.0f, 0);

    // Begin the scene.  Start rendering.
    g_D3DDevice->BeginScene();

    // Apply the view (camera).
    g_D3DDevice->SetTransform(D3DTS_VIEW, &g_ViewMatrix);

    // Draw square.
    g_D3DDevice->SetTexture(0, g_Texture);
    g_D3DDevice->SetStreamSource(0, g_VertexBuffer, 0, sizeof(stD3DVertex));
    g_D3DDevice->SetFVF(D3DFVF_VERTEX);
    g_D3DDevice->DrawPrimitive(D3DPT_TRIANGLELIST, 0, 2);

    // End the scene.  Stop rendering.
    g_D3DDevice->EndScene();

    // Display the scene.
    g_D3DDevice->Present(NULL, NULL, NULL, NULL);
}


void Shutdown()
{
    if(g_D3DDevice != NULL) g_D3DDevice->Release();
    g_D3DDevice = NULL;

    if(g_D3D != NULL) g_D3D->Release();
    g_D3D = NULL;

    if(g_VertexBuffer != NULL) g_VertexBuffer->Release();
    g_VertexBuffer = NULL;

    if(g_Texture != NULL) g_Texture->Release();
    g_Texture = NULL;
}

　　

在Direct3D 中，雾化是通过将景物颜色与雾的颜色，以随物体到观察点距离增加而衰减的混合因子混合而实现的。

       两种雾化方法：顶点雾化和像素雾化。

       三种雾化公式：线性雾化，指数雾化，指数平方雾化。

       两种雾化处理：基于深度的雾化处理和基于范围的雾化处理。基于深度是指两个点之间的深度（Z）差值，基于范围则是两点间的直线距离。Direct3D默认的是基于深度的雾化。可设置基于范围的雾化，但要先检测设备是否支持:

       g_pd3dDevice->GetDeviceCaps(&staps);

       if ( stCaps.RasterCaps & D3DPASTERCAPS_FOGRANGE )

            return TRUE;

       Direct3D默认禁用雾化效果，可以激活雾化：g_pd3dDevice->SetRendState( D3DRS_FOGENABLE, true );

       设置雾的颜色 g_pd3dDevice->SetRendState( D3DRS_FOGCOLOR, 0xffffffff); //白色

       根据按键消息进行多种雾化效果的切换

        if (gInputSystem->KeyDown(DIK_V))
        {
             //禁用雾化
             g_pd3dDevice->SetRenderState( D3DRS_FOGENABLE,FALSE );
        }

        

        if (gInputSystem->KeyDown(DIK_M))
        {

             g_pd3dDevice->SetRenderState( D3DRS_FOGENABLE,TRUE );
             //设置雾化混合因子计算公式 :  指数雾化
             g_pd3dDevice->GetDevice()->SetRenderState(D3DRS_FOGTABLEMODE, D3DFOG_EXP);
             //设置雾的浓度

             static float fogDensity = 0.005f; 
             g_pd3dDevice->SetRenderState(D3DRS_FOGDENSITY, *(DWORD*)&fogDensity);
        }

        

        if (gInputSystem->KeyDown(DIK_N))
        {

             g_pd3dDevice->SetRenderState( D3DRS_FOGENABLE,TRUE );

             //激活基于范围的雾化
             g_pd3dDevice->SetRenderState( D3DRS_RANGEFOGENABLE,TRUE );

             //设置雾化混合因子计算公式  :  线性雾化
             g_pd3dDevice->SetRenderState(D3DRS_FOGTABLEMODE, D3DFOG_LINEAR);
             //设置线性雾化开始位置和结束位置
             static float fogStart = 20;
             static float fogEnd = 200;
             g_pd3dDevice->SetRenderState(D3DRS_FOGSTART,*(DWORD*)&fogStart);     

             g_pd3dDevice->SetRenderState(D3DRS_FOGEND,*(DWORD*)&fogEnd);

        }

        
        if (gInputSystem->KeyDown(DIK_B))
        {
             g_pd3dDevice->SetRenderState( D3DRS_FOGENABLE,TRUE );
             //设置雾化混合因子计算公式 :  指数平方雾化
             g_pd3dDevice->SetRenderState(D3DRS_FOGTABLEMODE, D3DFOG_EXP2);
             //设置雾的浓度

             static float fogDensity = 0.01f;
             g_pd3dDevice->SetRenderState(D3DRS_FOGDENSITY, *(DWORD*)&fogDensity);
        }

        

        其中设置雾化混合因子计算公式时，SetRenderState的第一个参数可以是：

        D3DRS_FOGTABLEMODE(像素雾化)  或  D3DRS_FOGVERTEXMODE(顶点雾化)