【Direct3D】使用深度检测画两个平面

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本文系学习 DirectX tutorial 笔记，原文参考 directxtutorial.com/Lesson.aspx?lessonid=9-4-6

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画两个三角形，大三角形在前，小三角形在后面。当大三角形被渲染时，小三角形写入后台缓存。由于后台缓存的图形总是被画在最前面，

所以通常我们看到图片下面图片中的左图。而不是我们想看到的右图

Direct3D提供了深度检测(Z-buffer )来解决此类问题。

Z-Buffer，通常也称为深度缓存，是用来记录屏幕中模型到摄像机的距离的的缓存，如下图所示，当绘制一个像素的时候，总是选取距离

摄像机最近的pixel到后台缓存，同时，存储起来当前像素的深度值，这样下一个模型绘制时到这个位置时可以比较深度，决定画那个模型

关于Z-Buffer 有3个关键点：

1. 设置合适的显示参数；

D3DPRESENT_PARAMETERS d3dpp; ZeroMemory(&d3dpp, sizeof(d3dpp)); d3dpp.Windowed = FALSE; d3dpp.SwapEffect = D3DSWAPEFFECT_DISCARD; d3dpp.hDeviceWindow = hWnd; d3dpp.BackBufferFormat = D3DFMT_X8R8G8B8; d3dpp.BackBufferWidth = SCREEN_WIDTH; d3dpp.BackBufferHeight = SCREEN_HEIGHT; d3dpp.EnableAutoDepthStencil = TRUE;          // tells Direct3D to automaticlly create the z_buffer d3dpp.AutoDepthStencilFormat = D3DFMT_D16;  //each pixels is 16-bit

2. 打开z_buffer；

d3ddev->SetRenderState(D3DRS_LIGHTING, FALSE);    // turn off the 3D lighting d3ddev->SetRenderState(D3DRS_ZENABLE, TRUE);    // turn on the z-buffer

3. z_buffer 设为1

d3ddev->Clear(0, NULL, D3DCLEAR_TARGET, D3DCOLOR_XRGB(0, 0, 0), 1.0f, 0); d3ddev->Clear(0, NULL, D3DCLEAR_ZBUFFER, D3DCOLOR_XRGB(0, 0, 0), 1.0f, 0);

全部代码如下：

// include the basic windows header files and the Direct3D header file#include <windows.h>#include <windowsx.h>#include <d3d9.h>#include <d3dx9.h>// define the screen resolution#define SCREEN_WIDTH 800#define SCREEN_HEIGHT 600// include the Direct3D Library files#pragma comment (lib, "d3d9.lib")#pragma comment (lib, "d3dx9.lib")// global declarationsLPDIRECT3D9 d3d;    // the pointer to our Direct3D interfaceLPDIRECT3DDEVICE9 d3ddev;    // the pointer to the device classLPDIRECT3DVERTEXBUFFER9 v_buffer = NULL;    // the pointer to the vertex buffer// function prototypesvoid initD3D(HWND hWnd);    // sets up and initializes Direct3Dvoid render_frame(void);    // renders a single framevoid cleanD3D(void);    // closes Direct3D and releases memoryvoid init_graphics(void);    // 3D declarationsstruct CUSTOMVERTEX {FLOAT X, Y, Z; DWORD COLOR;};#define CUSTOMFVF (D3DFVF_XYZ | D3DFVF_DIFFUSE)// the WindowProc function prototypeLRESULT CALLBACK WindowProc(HWND hWnd, UINT message, WPARAM wParam, LPARAM lParam);// the entry point for any Windows programint WINAPI WinMain(HINSTANCE hInstance,                   HINSTANCE hPrevInstance,                   LPSTR lpCmdLine,                   int nCmdShow){    HWND hWnd;    WNDCLASSEX wc;    ZeroMemory(&wc, sizeof(WNDCLASSEX));    wc.cbSize = sizeof(WNDCLASSEX);    wc.style = CS_HREDRAW | CS_VREDRAW;    wc.lpfnWndProc = WindowProc;    wc.hInstance = hInstance;    wc.hCursor = LoadCursor(NULL, IDC_ARROW);    wc.lpszClassName = L"WindowClass";    RegisterClassEx(&wc);    hWnd = CreateWindowEx(NULL, L"WindowClass", L"Our Direct3D Program",                          WS_OVERLAPPEDWINDOW, 0, 0, SCREEN_WIDTH, SCREEN_HEIGHT,                          NULL, NULL, hInstance, NULL);    ShowWindow(hWnd, nCmdShow);    // set up and initialize Direct3D    initD3D(hWnd);    // enter the main loop:    MSG msg;    while(TRUE)    {        while(PeekMessage(&msg, NULL, 0, 0, PM_REMOVE))        {            TranslateMessage(&msg);            DispatchMessage(&msg);        }        if(msg.message == WM_QUIT)            break;        render_frame();    }    // clean up DirectX and COM    cleanD3D();    return msg.wParam;}// this is the main message handler for the programLRESULT CALLBACK WindowProc(HWND hWnd, UINT message, WPARAM wParam, LPARAM lParam){    switch(message)    {        case WM_DESTROY:            {                PostQuitMessage(0);                return 0;            } break;    }    return DefWindowProc (hWnd, message, wParam, lParam);}// this function initializes and prepares Direct3D for usevoid initD3D(HWND hWnd){    d3d = Direct3DCreate9(D3D_SDK_VERSION);    D3DPRESENT_PARAMETERS d3dpp;    ZeroMemory(&d3dpp, sizeof(d3dpp));    d3dpp.Windowed = TRUE;    d3dpp.SwapEffect = D3DSWAPEFFECT_DISCARD;    d3dpp.hDeviceWindow = hWnd;    d3dpp.BackBufferFormat = D3DFMT_X8R8G8B8;    d3dpp.BackBufferWidth = SCREEN_WIDTH;    d3dpp.BackBufferHeight = SCREEN_HEIGHT;    d3dpp.EnableAutoDepthStencil = TRUE;    // automatically run the z-buffer for us    d3dpp.AutoDepthStencilFormat = D3DFMT_D16;    // 16-bit pixel format for the z-buffer    // create a device class using this information and the info from the d3dpp stuct    d3d->CreateDevice(D3DADAPTER_DEFAULT,                      D3DDEVTYPE_HAL,                      hWnd,                      D3DCREATE_SOFTWARE_VERTEXPROCESSING,                      &d3dpp,                      &d3ddev);    init_graphics();    // call the function to initialize the triangle    d3ddev->SetRenderState(D3DRS_LIGHTING, FALSE);    // turn off the 3D lighting    d3ddev->SetRenderState(D3DRS_CULLMODE, D3DCULL_NONE);    // both sides of the triangles<span style="white-space:pre"></span>d3ddev->SetRenderState(D3DRS_ZENABLE, true);    // turn on the z-buffer}// this is the function used to render a single framevoid render_frame(void){    d3ddev->Clear(0, NULL, D3DCLEAR_TARGET, D3DCOLOR_XRGB(0, 0, 0), 1.0f, 0);    d3ddev->Clear(0, NULL, D3DCLEAR_ZBUFFER, D3DCOLOR_XRGB(0, 0, 0), 1.0f, 0);    d3ddev->BeginScene();    // select which vertex format we are using    d3ddev->SetFVF(CUSTOMFVF);    // set the view transform    D3DXMATRIX matView;    // the view transform matrix    D3DXMatrixLookAtLH(&matView,                       &D3DXVECTOR3 (0.0f, 0.0f, 15.0f),   // the camera position                       &D3DXVECTOR3 (0.0f, 0.0f, 0.0f),    // the look-at position                       &D3DXVECTOR3 (0.0f, 1.0f, 0.0f));    // the up direction    d3ddev->SetTransform(D3DTS_VIEW, &matView);    // set the view transform to matView    // set the projection transform    D3DXMATRIX matProjection;    // the projection transform matrix    D3DXMatrixPerspectiveFovLH(&matProjection,                               D3DXToRadian(45),    // the horizontal field of view                               (FLOAT)SCREEN_WIDTH / (FLOAT)SCREEN_HEIGHT, // aspect ratio                               1.0f,    // the near view-plane                               100.0f);    // the far view-plane    d3ddev->SetTransform(D3DTS_PROJECTION, &matProjection);     // set the projection    // select the vertex buffer to display    d3ddev->SetStreamSource(0, v_buffer, 0, sizeof(CUSTOMVERTEX));    D3DXMATRIX matTranslateA;    // a matrix to store the translation for triangle A    D3DXMATRIX matTranslateB;    // a matrix to store the translation for triangle B    D3DXMATRIX matRotateY;    // a matrix to store the rotation for each triangle    static float index = 0.0f; index+=0.05f; // an ever-increasing float value    // build MULTIPLE matrices to translate the model and one to rotate    D3DXMatrixTranslation(&matTranslateA, 0.0f, 0.0f, 2.0f);    D3DXMatrixTranslation(&matTranslateB, 0.0f, 0.0f, -2.0f);    D3DXMatrixRotationY(&matRotateY, index);    // the front side    // tell Direct3D about each world transform, and then draw another triangle    d3ddev->SetTransform(D3DTS_WORLD, &(matTranslateA * matRotateY));    d3ddev->DrawPrimitive(D3DPT_TRIANGLELIST, 0, 1);    d3ddev->SetTransform(D3DTS_WORLD, &(matTranslateB * matRotateY));    d3ddev->DrawPrimitive(D3DPT_TRIANGLELIST, 0, 1);    d3ddev->EndScene();     d3ddev->Present(NULL, NULL, NULL, NULL);}// this is the function that cleans up Direct3D and COMvoid cleanD3D(void){    v_buffer->Release();    // close and release the vertex buffer    d3ddev->Release();    // close and release the 3D device    d3d->Release();    // close and release Direct3D}// this is the function that puts the 3D models into video RAMvoid init_graphics(void){    // create the vertices using the CUSTOMVERTEX struct    CUSTOMVERTEX vertices[] =     {        { 3.0f, -3.0f, 0.0f, D3DCOLOR_XRGB(0, 0, 255), },        { 0.0f, 3.0f, 0.0f, D3DCOLOR_XRGB(0, 255, 0), },        { -3.0f, -3.0f, 0.0f, D3DCOLOR_XRGB(255, 0, 0), },    };    // create a vertex buffer interface called v_buffer    d3ddev->CreateVertexBuffer(3*sizeof(CUSTOMVERTEX),                               0,                               CUSTOMFVF,                               D3DPOOL_MANAGED,                               &v_buffer,                               NULL);    VOID* pVoid;    // a void pointer    // lock v_buffer and load the vertices into it    v_buffer->Lock(0, 0, (void**)&pVoid, 0);    memcpy(pVoid, vertices, sizeof(vertices));    v_buffer->Unlock();}

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