L_DoubleBufferEnd

Functions

• L_DoubleBufferEnable
• L_DoubleBufferCreateHandle
• L_DoubleBufferDestroyHandle
• L_DoubleBufferBegin

Topics

• Raster Image Functions: Displaying Images
• Minimizing Flicker With Double Buffering

Example

To see how double buffering can be used
in an application, see the source code for the API annotation
demo.
This sample illustrates double buffering by bouncing a ball around
a window that contains an image
For simplicity, we assume both the window the hDC are 24 bit
Run the example twice --

• once with bDoubleBuffer set to FALSE
• once with bDoubleBuffer set to TRUE
  to see the difference
  hWnd -- window to paint image and bounce ball
  pszFile -- file name of image to load
  bDoubleBuffer - flag saying whether or not to double buffer the paints
  

  #define BALL_RADIUS 30 
  L_INT DoubleBufferEndExample(L_HWND        hWnd, 
                                               L_TCHAR*    pszFile, 
                                               L_BOOL      bDoubleBuffer) 
  { 
     HBRUSH         hBrush; 
     BITMAPHANDLE   Bitmap; 
     L_HANDLE       hDoubleBufferHandle; 
     L_INT          cx, cy; 
     HDC            hDC, hMemDC; 
     RECT           rcClient; 
     RECT           rcBitmap; 
     RECT           rcBall; 
     L_INT          dx, dy; 
     L_INT          i; 
     L_INT          nRet; 
   
     nRet = L_LoadBitmap(pszFile, &Bitmap, sizeof(BITMAPHANDLE), 0, ORDER_BGRORGRAY, NULL, NULL); 
     if (nRet != SUCCESS) 
     { 
        MessageBox(hWnd, TEXT("Failed to load image"), TEXT("Error"), MB_OK); 
        return nRet; 
     } 
   
     hBrush = CreateSolidBrush( RGB(100,100,100)); 
     nRet = L_DoubleBufferCreateHandle(&hDoubleBufferHandle); 
     if(nRet != SUCCESS) 
        return nRet; 
   
     nRet = L_DoubleBufferEnable(hDoubleBufferHandle, bDoubleBuffer); 
     if(nRet != SUCCESS) 
        return nRet; 
      
     GetClientRect(hWnd, &rcClient); 
     cx = rcClient.right  - rcClient.left; 
     cy = rcClient.bottom - rcClient.top; 
     hDC = GetDC(hWnd); 
   
     rcBitmap.left = 0; 
     rcBitmap.top = 0; 
     rcBitmap.right = BITMAPWIDTH(&Bitmap); 
     rcBitmap.bottom = BITMAPWIDTH(&Bitmap); 
   
     SetRect(&rcBall, 0, 0, BALL_RADIUS, BALL_RADIUS); 
     dx = dy = 1; 
     for (i=0; i<2000; i++) 
     { 
        // Double buffer painting the image and the moving ball 
        hMemDC = L_DoubleBufferBegin(hDoubleBufferHandle, hDC, cx, cy); 
        FillRect(hMemDC, &rcClient, hBrush); 
        nRet = L_PaintDC(hMemDC, &Bitmap, NULL, NULL, &rcBitmap, NULL, SRCCOPY);  
        if(nRet != SUCCESS) 
           return nRet; 
        Ellipse(hMemDC, rcBall.left, rcBall.top, rcBall.right, rcBall.bottom); 
        nRet = L_DoubleBufferEnd(hDoubleBufferHandle, hDC); 
        if(nRet != SUCCESS) 
           return nRet; 
   
        if ((rcBall.bottom) > rcClient.bottom) 
           dy = -1; 
        if (rcBall.top < 0) 
           dy = 1; 
        if (rcBall.left < 0) 
           dx = 1; 
        if ((rcBall.right) > rcClient.right) 
           dx = -1; 
        OffsetRect(&rcBall, dx, dy); 
     } 
   
     // Cleanup 
     L_FreeBitmap(&Bitmap); 
     L_DoubleBufferDestroyHandle(hDoubleBufferHandle); 
     DeleteObject(hBrush); 
     return SUCCESS; 
  }