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BOOL CDib::Read(CFile* pFile)
{
 // 1. read file header to get size of info hdr + color table
 // 2. read info hdr (to get image size) and color table
 // 3. read image
 // can't use bfSize in file header
 
 // Çå³ýDIB
 Empty();
 
 int nCount, nSize;
 BITMAPFILEHEADER bmfh;//λͼÎļþÍ·½á¹¹£¬¶¨ÒåÁËÒ»¸ö¶ÔÏó
 
 // ³¢ÊÔ¶ÁÈ¡BMPÎļþ
 try
 {
  // ¶ÁBMPÎļþÍ·
  nCount = pFile->Read((LPVOID) &bmfh, sizeof(BITMAPFILEHEADER));//λͼÎļþÍ·´æ·ÅÔÚλͼÎļþµÄ¿ªÍ·²¿·Ö£¬¾ßÌåΪʲô¿ÉÒÔÑо¿Î»Í¼ÎļþµÄÏà¹ØÄÚÈÝ¡£
  
  // Åж϶ÁÈ¡ÎļþÍ·µÄ´óСÊÇ·ñÕýÈ·
  if(nCount != sizeof(BITMAPFILEHEADER))
  {
   // ¶ÁÎļþ³ö´í
   throw new CException;
  }
  
  // ÅжÏÊÇ·ñÊÇ"BM"
  if(bmfh.bfType != 0x4d42)//λͼÎļþÍ·½á¹¹ÌåµÄÒ»¸ö×ֶΣ¬Ö»ÒªÊÇλͼÎļþ£¬Õâ¸öֵʼÖÕÊÇ¡°BM¡±
  {
   // ²»ÊÇBMPÎļþ£¬Å׳öÒì³£
   throw new CException;
  }
  nSize = bmfh.bfOffBits - sizeof(BITMAPFILEHEADER);
  m_lpBMIH = (LPBITMAPINFOHEADER) new char[nSize];
  m_nBmihAlloc = m_nImageAlloc = crtAlloc;
  nCount = pFile->Read(m_lpBMIH, nSize); // info hdr & color table
  ComputeMetrics();//compute:¼ÆËã;Metrics:³ß´ç
  ComputePaletteSize(m_lpBMIH->biBitCount);
  MakePalette();
  m_lpImage = (LPBYTE) new char[m_dwSizeImage];
  nCount = pFile->Read(m_lpImage, m_dwSizeImage); // image only
 }
 catch(CException* pe)
 {
  AfxMessageBox("Read error");
  pe->Delete();
  return FALSE;
 }
 return TRUE;
}