32. 细节映射

通常会多次要在3D场景中显示大量的细节。例如，混凝土上的裂纹，或粗糙墙面的凸凹不平之处。也许并不总是想在纹理图像自身包含这种细节。通常，一些彩色图纹理虽然从远处看的时候它们很好，但靠近看时，也许会让观察者觉得有些模糊。使用一种名为细节映射的技术有助于解决这些问题，或至少得到改善。

       细节图是一个灰度图，保存小而精确的细节内容。当将其和颜色图一起施加到表面上时，最终的图像看上去原始图像好像有更多的细节。同样，使用细节图时，颜色图在从上靠近看时，看上去不模糊。使用细节图为表面增加细节，给图增加小的裂纹以及线条，这样可以提高表面的真实感。对墙和类似表面更是如此。

       细节映射的演示成名为DetailMapping，它位于本书配套光盘的CHAPTER6文件夹中。它将加载两个纹理图像，对它们实现多纹理映射，并将它们显示在一个正方形表面上。在合并两幅纹理图像时，通过一个有符号操作将细节添加到基图上。纹理图像中有符号值从-128~128，而无符号值从0~255。细节图中较亮的值将会增亮基图，而较黑的值则产生反面的效果。只有0不会对最终的图像产生任何效果，因为是正在添加图像而不是对图像作调制，就像在多纹理演示程序中的做法一样。

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

#define WINDOW_CLASS    "UGPDX"
#define WINDOW_NAME     "Detail Mapping"
#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;
LPDIRECT3DTEXTURE9 g_Texture2 = NULL;

// A structure for our custom vertex type
struct stD3DVertex
{
    float x, y, z;
    unsigned long color;
    float tu, tv;
    float tu2, tv2;
};

// Our custom FVF, which describes our custom vertex structure
#define D3DFVF_VERTEX (D3DFVF_XYZ | D3DFVF_DIFFUSE | D3DFVF_TEX2)


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()
{
    // Fill in our structure to draw an object.
    // x, y, z, color, texture coords.
    stD3DVertex objData[] =
    {
        {-1.5f, -0.5f, 0.0f, D3DCOLOR_XRGB(255,255,255), 0.0f, 1.0f, 0.0f, 1.0f},
        {1.5f, -0.5f,  0.0f, D3DCOLOR_XRGB(255,255,255), 1.0f, 1.0f, 1.0f, 1.0f},
        {1.5f, -0.5f, 3.0f, D3DCOLOR_XRGB(255,255,255), 1.0f, 0.0f, 1.0f, 0.0f},

        {1.5f, -0.5f, 3.0f, D3DCOLOR_XRGB(255,255,255), 1.0f, 0.0f, 1.0f, 0.0f},
        {-1.5f, -0.5f, 3.0f, D3DCOLOR_XRGB(255,255,255), 0.0f, 0.0f, 0.0f, 0.0f},
        {-1.5f, -0.5f, 0.0f, D3DCOLOR_XRGB(255,255,255), 0.0f, 1.0f, 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;

    if(D3DXCreateTextureFromFile(g_D3DDevice, "detail.tga",
        &g_Texture2) != 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, -1.0f);
    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(0,0,0), 1.0f, 0);

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

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

    // Set the texture stages for the first texture unit (image).
    g_D3DDevice->SetSamplerState(0, D3DSAMP_MINFILTER, D3DTEXF_LINEAR);
    g_D3DDevice->SetSamplerState(0, D3DSAMP_MAGFILTER, D3DTEXF_LINEAR);

    /*
    如果要模拟一块粗糙的石灰泥墙壁，可以通过细节映射（detail mapping）来实现。
    实现过程是：将基础贴图（也就是第一张纹理）的颜色未经修改便作为第二个纹理操作
    阶段中的第二个参数，然后通过D3DTOP_ADDSIGNED将灰色的细节纹理与基础贴图相加。
    这个操作本质上是做了一个加法，只是使用了有符号的颜色值来代替平时使用的无符号值。
    在对两张纹理的像素颜色进行D3DTOP_ADDSIGNED操作时，它将参数的每个成分相加后再减去
    偏移量0.5，从而使有效值域变为-0.5 ~ 0.5。对一些比较旧的显卡，当其不能支持
    D3DTOP_ADDSIGNED操作时，可以使用D3DTOP_MODULATE2X代替D3DTOP_ADDSIGNED操作进行模拟。
    */

    g_D3DDevice->SetTextureStageState(0, D3DTSS_TEXCOORDINDEX, 0);
    // 颜色混合方式--使用当前颜色作为第一个texture stage的输出
    g_D3DDevice->SetTextureStageState(0, D3DTSS_COLOROP,   D3DTOP_SELECTARG1);
    // 颜色混合的第一个参数的来源--纹理的颜色
    g_D3DDevice->SetTextureStageState(0, D3DTSS_COLORARG1, D3DTA_TEXTURE);

    // Set the texture stages for the second texture unit (image).
    g_D3DDevice->SetSamplerState(1, D3DSAMP_MINFILTER, D3DTEXF_LINEAR);
    g_D3DDevice->SetSamplerState(1, D3DSAMP_MAGFILTER, D3DTEXF_LINEAR);

    g_D3DDevice->SetTextureStageState(1, D3DTSS_TEXCOORDINDEX, 1);
    g_D3DDevice->SetTextureStageState(1, D3DTSS_COLOROP, D3DTOP_ADDSIGNED);
    g_D3DDevice->SetTextureStageState(1, D3DTSS_COLORARG1, D3DTA_TEXTURE);
    g_D3DDevice->SetTextureStageState(1, D3DTSS_COLORARG2, D3DTA_CURRENT);

    // Draw square.
    g_D3DDevice->SetTexture(0, g_Texture);
    g_D3DDevice->SetTexture(1, g_Texture2);
    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;

    if(g_Texture2 != NULL) g_Texture2->Release();
    g_Texture2 = NULL;
}