BitBlt的程序

/*-----------------------------------------
   HELLOBIT.C -- Bitmap Demonstration
                 (c) Charles Petzold, 1998
  -----------------------------------------*/
 
#include <windows.h>
#include "resource.h"

LRESULT CALLBACK WndProc (HWND, UINT, WPARAM, LPARAM) ;

int WINAPI WinMain (HINSTANCE hInstance, HINSTANCE hPrevInstance,
                    PSTR szCmdLine, int iCmdShow)
{
     static TCHAR szAppName [] = TEXT ("HelloBit") ;
     HWND         hwnd ;
     MSG          msg ;
     WNDCLASS     wndclass ;

     wndclass.style         = CS_HREDRAW | CS_VREDRAW ;
     wndclass.lpfnWndProc   = WndProc ;
     wndclass.cbClsExtra    = 0 ;
     wndclass.cbWndExtra    = 0 ;
     wndclass.hInstance     = hInstance ;
     wndclass.hIcon         = LoadIcon (NULL, IDI_APPLICATION) ;
     wndclass.hCursor       = LoadCursor (NULL, IDC_ARROW) ;
     wndclass.hbrBackground = (HBRUSH) GetStockObject (WHITE_BRUSH) ;
     wndclass.lpszMenuName  = szAppName ;
     wndclass.lpszClassName = szAppName ;
     
     if (!RegisterClass (&wndclass))
     {
          MessageBox (NULL, TEXT ("This program requires Windows NT!"),
                      szAppName, MB_ICONERROR) ;
          return 0 ;
     }
     
     hwnd = CreateWindow (szAppName, TEXT ("HelloBit"), 
                          WS_OVERLAPPEDWINDOW, 
                          CW_USEDEFAULT, CW_USEDEFAULT,
                          CW_USEDEFAULT, CW_USEDEFAULT,
                          NULL, NULL, hInstance, NULL) ;

     ShowWindow (hwnd, iCmdShow) ;
     UpdateWindow (hwnd) ;

     while (GetMessage (&msg, NULL, 0, 0))
     {
          TranslateMessage (&msg) ;
          DispatchMessage (&msg) ;
     }
     return msg.wParam ;
}

LRESULT CALLBACK WndProc (HWND hwnd, UINT message, WPARAM wParam, LPARAM lParam)
{
     static HBITMAP hBitmap ;
     static HDC     hdcMem ;
     static int     cxBitmap, cyBitmap, cxClient, cyClient, iSize = IDM_BIG ;
     static TCHAR * szText = TEXT (" Hello, world! ") ;
     HDC            hdc ;
     HMENU          hMenu ;
     int            x, y ;
     PAINTSTRUCT    ps ;
     SIZE           size ;
     
     switch (message)
     {
     case WM_CREATE:
			 // 窗口DC
          hdc = GetDC (hwnd) ;
			 // 兼容窗口的内存DC
          hdcMem  = CreateCompatibleDC (hdc) ;
			//得到字符串的长度和高度
          GetTextExtentPoint32 (hdc, szText, lstrlen (szText), &size) ;
          cxBitmap = size.cx ;
          cyBitmap = size.cy ;
			//创建一个兼容位图
          hBitmap = CreateCompatibleBitmap (hdc, cxBitmap, cyBitmap) ;
			//释放创建的窗口DC
          ReleaseDC (hwnd, hdc) ;
			// 把兼容位图选入到内存DC去

          SelectObject (hdcMem, hBitmap) ;
          TextOut (hdcMem, 0, 0, szText, lstrlen (szText)) ;
          return 0 ;

     case WM_SIZE:
          cxClient = LOWORD (lParam) ;
          cyClient = HIWORD (lParam) ;
          return 0 ;

     case WM_COMMAND:
          hMenu = GetMenu (hwnd) ;

          switch (LOWORD (wParam))
          {
          case IDM_BIG:
          case IDM_SMALL:
               CheckMenuItem (hMenu, iSize, MF_UNCHECKED) ;
               iSize = LOWORD (wParam) ;
               CheckMenuItem (hMenu, iSize, MF_CHECKED) ;
               InvalidateRect (hwnd, NULL, TRUE) ;
               break ;
          }
          return 0 ;

     case WM_PAINT:
          hdc = BeginPaint (hwnd, &ps) ;

          switch (iSize)
          {
          case IDM_BIG:
			  // 拉伸位图，显示客户区
               StretchBlt (hdc, 0, 0, cxClient, cyClient, 
                           hdcMem, 0, 0, cxBitmap, cyBitmap, SRCCOPY) ;
               break ;

          case IDM_SMALL:
               for (y = 0 ; y < cyClient ; y += cyBitmap)
               for (x = 0 ; x < cxClient ; x += cxBitmap)
               {
				   // 只能显示实际大小
                    BitBlt (hdc, x, y, cxBitmap, cyBitmap, 
                            hdcMem, 0, 0, SRCCOPY) ;
               }
               break ;
          }

          EndPaint (hwnd, &ps) ;
          return 0 ;

     case WM_DESTROY:
          DeleteDC (hdcMem) ;
          DeleteObject (hBitmap) ;
          PostQuitMessage (0) ;
          return 0 ;
     }
     return DefWindowProc (hwnd, message, wParam, lParam) ;
}