在BitBlt函数中，目标图像和源图像的大小一样，是因为函数只有两个参数来指定宽和高，如果想要复制是拉伸或压缩图像的大小，可以使用StretchBlt函数

StretchBlt(hdcDst,xDst,yDst,cxDst,cyDst,hdcSrc,xSrc,ySrc,cxSrc,cySrc,dwRop);

下面这个程序展示了一下StretchBlt函数的功能，它把整个客户区填满成系统菜单图标了，改变某些参数的值，可以使得图标上下或左右颠倒

#include<windows.h>
LRESULT CALLBACK WindowProc(
              HWND hwnd,      // handle to window
              UINT uMsg,      // message identifier
              WPARAM wParam,  // first message parameter
              LPARAM lParam   // second message parameter
              );
int WINAPI WinMain(
           HINSTANCE hInstance,      // handle to current instance
           HINSTANCE hPrevInstance,  // handle to previous instance
           LPSTR lpCmdLine,          // command line
           int nCmdShow              // show state
           )
{
  static  TCHAR szAppName[]=TEXT("leidemingzi");
  HWND hwnd;
  MSG msg;
  WNDCLASS wndclass;
  wndclass.cbClsExtra=0;
  wndclass.cbWndExtra=0;
  wndclass.hbrBackground=(HBRUSH)GetStockObject(WHITE_BRUSH);
  wndclass.hCursor=LoadCursor(NULL,IDC_ARROW);
  wndclass.hIcon=LoadIcon(NULL,IDI_ERROR);
  wndclass.hInstance=hInstance;
  wndclass.lpfnWndProc=WindowProc;
  wndclass.lpszClassName=szAppName;
  wndclass.lpszMenuName=NULL;
  wndclass.style=CS_HREDRAW|CS_VREDRAW;
  if(!RegisterClass(&wndclass))
  {
    MessageBox(NULL,TEXT("the program require the windows nt"),TEXT("tips"),MB_ICONERROR);
    return 0;
  }
  hwnd=CreateWindow(
    szAppName,  // registered class name
    TEXT("this is title"), // window name
    WS_OVERLAPPEDWINDOW,        // window style
    CW_USEDEFAULT,                // horizontal position of window
    CW_USEDEFAULT,                // vertical position of window
    CW_USEDEFAULT,           // window width
    CW_USEDEFAULT,          // window height
    NULL,      // handle to parent or owner window
    NULL,          // menu handle or child identifier
    hInstance,  // handle to application instance
    NULL        // window-creation data
    );
  ShowWindow(hwnd,nCmdShow);
  UpdateWindow(hwnd);
  while(GetMessage(&msg,NULL,0,0))
  {
    TranslateMessage(&msg);
    DispatchMessage(&msg);
  }

  return msg.wParam;
}
LRESULT CALLBACK WindowProc(
              HWND hwnd,      // handle to window
              UINT uMsg,      // message identifier
              WPARAM wParam,  // first message parameter
              LPARAM lParam   // second message parameter
              )
{
  static int cxClient,cyClient,cxSource,cySource;
  HDC hdcClient,hdcWindow;
  PAINTSTRUCT ps;
  switch(uMsg)
  {
  case WM_CREATE:
    cxSource=GetSystemMetrics(SM_CXSIZEFRAME)+GetSystemMetrics(SM_CXSIZE);
    cySource=GetSystemMetrics(SM_CYSIZEFRAME)+GetSystemMetrics(SM_CYCAPTION);
    return 0;
  case WM_SIZE:
    cxClient=LOWORD(lParam);
    cyClient=HIWORD(lParam);
  case WM_PAINT:
    hdcClient=BeginPaint(hwnd,&ps);
    hdcWindow=GetWindowDC(hwnd);
    StretchBlt(hdcClient,0,0,cxClient,cyClient,hdcWindow,0,0,cxSource,cySource,MERGECOPY);
    ReleaseDC(hwnd,hdcWindow);
    EndPaint(hwnd,&ps);
    return 0;
  case WM_DESTROY:
    PostQuitMessage(0);
    return 0;
  }
  return DefWindowProc(hwnd,uMsg,wParam,lParam);
}