How to snap an OpenGL client and send it to the clipboard

本文介绍了一种方法，能够捕获OpenGL客户端区域的画面并将其发送到剪贴板，以便于在图像编辑器、PowerPoint等应用中使用。该方法通过获取OpenGL客户端的几何尺寸，创建位图并读取像素数据，最终将位图信息打包为DIB格式放入剪贴板。

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This article demonstrates how to snap an OpenGL client and send it to ClipBoard.

We suppose your screen configuration is set to true color.
We could send the same buffer in a .bmp file in a few lines too....

// Snap OpenGL client and send it to ClipBoard 
// so that you can insert it in your favorite 
// image editor, Powerpoint, etc... 
// Replace CRenderView by your own CView-derived class 
void CRenderView::SnapClient() 
{ 
 BeginWaitCursor();

 // Get client geometry 
 CRect rect; 
 GetClientRect(&rect); 
 CSize size(rect.Width(), rect.Height()); 
 TRACE("  client zone : (%d;%d)\n",size.cx,size.cy); 
 // Lines have to be 32 bytes aligned, suppose 24 bits per pixel 
 // I just cropped it 
 size.cx -= size.cx % 4; 
 TRACE("  final client zone : (%d;%d)\n", size.cx, size.cy);

 // Create a bitmap and select it in the device context 
 // Note that this will never be used ;-) but no matter 
 CBitmap bitmap; 
 CDC *pDC = GetDC(); 
 CDC MemDC; 
 ASSERT(MemDC.CreateCompatibleDC(NULL)); 
 ASSERT(bitmap.CreateCompatibleBitmap(pDC, size.cx, size.cy)); 
 MemDC.SelectObject(&bitmap);

 // Alloc pixel bytes 
 int NbBytes = 3 * size.cx * size.cy; 
 unsigned char *pPixelData = new unsigned char[NbBytes];

 // Copy from OpenGL 
 ::glReadPixels(0, 0, size.cx, size.cy, GL_RGB,GL_UNSIGNED_BYTE, pPixelData);

 // Fill header 
 BITMAPINFOHEADER header; 
 header.biWidth  = size.cx; 
 header.biHeight = size.cy; 
 header.biSizeImage = NbBytes; 
 header.biSize   = 40; 
 header.biPlanes = 1; 
 header.biBitCount =  3 * 8; // RGB 
 header.biCompression = 0; 
 header.biXPelsPerMeter = 0; 
 header.biYPelsPerMeter = 0; 
 header.biClrUsed = 0; 
 header.biClrImportant = 0;

 // Generate handle 
 HANDLE handle = (HANDLE)::GlobalAlloc (GHND,sizeof(BITMAPINFOHEADER) + NbBytes); 
 if(handle != NULL) 
 { 
  // Lock handle 
  char *pData = (char *) ::GlobalLock((HGLOBAL)handle); 
  // Copy header and data 
  memcpy(pData,&header,sizeof(BITMAPINFOHEADER)); 
  memcpy(pData+sizeof(BITMAPINFOHEADER),pPixelData,NbBytes); 
  // Unlock 
  ::GlobalUnlock((HGLOBAL)handle);

  // Push DIB in clipboard 
  OpenClipboard(); 
  EmptyClipboard(); 
  SetClipboardData(CF_DIB,handle); 
  CloseClipboard(); 
 }

 // Cleanup 
 MemDC.DeleteDC(); 
 bitmap.DeleteObject(); 
 delete [] pPixelData;

 EndWaitCursor(); 
}