directx的简单例子（打开一个d3d窗口）注意的地方

#include <d3d9.h>
#include <Windows.h>

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

#define WINDOW_CLASS "UGPDX"
#define WINDOW_NAME  "Blank D3D Window"


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


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


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, 640, 480, GetDesktopWindow(), NULL,
                            wc.hInstance, NULL);
   g_D3D= Direct3DCreate9(D3D_SDK_VERSION);

    //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 = 640;
         d3dpp.BackBufferHeight = 480;
      }
   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;
      }

   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();

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