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L_DoubleBufferEnd

Summary

Displays the double buffered paint operations.

Syntax

#include "l_bitmap.h"

L_LTDIS_API L_INT L_DoubleBufferEnd(hDoubleBufferHandle, hDC)

Parameters

L_HANDLE hDoubleBufferHandle

Handle that identifies the double buffering process.

L_HDC hDC

Handle to the original target device context.

Returns

Value	Meaning
SUCCESS	The function was successful.
< 1	An error occurred. Refer to Return Codes.

Comments

Use L_DoubleBufferEnd when ready to paint all that has been double-buffered to the target hDC. All double buffered paint operations should be wrapped in L_DoubleBufferBegin and L_DoubleBufferEnd calls.

The hDC argument is the device context that you want to double buffer, which in this case should be the same as the hDC argument that was passed to L_DoubleBufferBegin.

Note that you must create a double buffer handle with L_DoubleBufferCreateHandle before calling this function.

For more information, see the topic Minimizing Flicker With Double Buffering.

Required DLLs and Libraries

LTDIS
For a listing of the exact DLLs and Libraries needed, based on the toolkit version, refer to Files To Be Included With Your Application.

Platforms

Win32, x64.

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; 
   L_TCHAR        buf[256]; 
 
   nRet = L_LoadBitmap(pszFile, &Bitmap, sizeof(BITMAPHANDLE), 0, ORDER_BGRORGRAY, NULL, NULL); 
   if (nRet != SUCCESS) 
   { 
      wsprintf(buf, TEXT("Error: Failed to load image.")); 
      _tprintf(_T("%s"), buf); 
 
      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); 
   nRet = L_DoubleBufferDestroyHandle(hDoubleBufferHandle); 
   DeleteObject(hBrush); 
 
   return nRet; 
}