VC截图及用AlphaBlend实现半透明位图

Requirements:

 Windows NT/2000/XP: Included in Windows 2000 and later.

 Windows 95/98/Me: Included in Windows 98 and later.

 Header: Declared in Wingdi.h; include Windows.h.

 Library: Included as a resource in Msimg32.dll.

 

示例 :

 

void CTestDlg::SaveBitmap(CDC* pDC,CRect rect,CString filename)

{ 

 CDC* memDC=new CDC;

 memDC->CreateCompatibleDC(pDC);

 CBitmap* bmp=new CBitmap;

 bmp->CreateCompatibleBitmap(pDC,rect.Width(),rect.Height());

 CBitmap* oldbitmap=memDC->SelectObject(bmp);

 // 此时的 bmp 就相当于一张桌布，在 memDC 中画线 etc 都是画在这张桌布上

 if(!memDC->BitBlt(0,0,rect.Width(),rect.Height(),pDC,0,0,SRCCOPY))

 {

   AfxMessageBox("BitBlt Error!");

   return;

 }

 memDC->Ellipse(0,0,100,100);

 memDC->SelectObject(oldbitmap);

 

 BITMAPINFO bi;

 bi.bmiHeader.biSize=sizeof(bi.bmiHeader);

 bi.bmiHeader.biWidth=rect.Width();

 bi.bmiHeader.biHeight=rect.Height();

 bi.bmiHeader.biPlanes=1;

 bi.bmiHeader.biBitCount=16;

 bi.bmiHeader.biCompression=BI_RGB;

 bi.bmiHeader.biSizeImage=0;

 bi.bmiHeader.biXPelsPerMeter=0;

 bi.bmiHeader.biYPelsPerMeter=0;

 bi.bmiHeader.biClrUsed=0;

 bi.bmiHeader.biClrImportant=0;

 

 int bitsize=rect.Width()*rect.Height()*2;

 BYTE* bits=new BYTE[bitsize];

 ::GetDIBits(memDC->m_hDC,*bmp,0,rect.Height(),bits,&bi,DIB_RGB_COLORS); 

  

 BITMAPFILEHEADER bf;

 bf.bfType=(int)'M'*256+'B';

 bf.bfSize=bitsize;//sizeof(bf);

 bf.bfOffBits=sizeof(bi.bmiHeader)+sizeof(bf);

 bf.bfReserved1=0;

 bf.bfReserved2=0;

 

 CFile f(filename,CFile::modeCreate|CFile::modeWrite);

 f.Write(&bf,sizeof(bf));// 注意是先写 bf, 再写 bi

 f.Write(&bi,sizeof(bi));

 f.Write(bits,bitsize);

 f.Close();

 

 delete[] bits;

 delete bmp;

 delete memDC;

}

 

 

将 memDC 上的位图半透明覆盖到 pDC 上

BLENDFUNCTION bm;

bm.BlendOp=AC_SRC_OVER;

bm.BlendFlags=0;

bm.SourceConstantAlpha=100;

bm.AlphaFormat=0; 

AlphaBlend(pDC->m_hDC,0,0,rect.Width(),rect.Height(),memDC->m_hDC,0,0,rect.Width(),rect.Height(),bm);