win32下handle转化为HBITMAP

//  handle to bitmap
HBITMAP hwndToHbitmap(HWND hwnd)
{

    // get the DC of the handle
    HDC hDC = GetDC(hwnd);

    // the rect struct
    RECT rect;
    // get the rect of the handle
    GetClientRect(hwnd, &rect);

    // create a compatible dc for the hDC
    HDC hDCMem = CreateCompatibleDC(hDC);

    // create a  compatible bitmap for the hDC
    HBITMAP hBitMap = CreateCompatibleBitmap(hDC, rect.right, rect.bottom);

    // selects an object into a specified device context
    // the second parameter is als brush font pen and region
    // the first parameter is a handle point to the device context
    HBITMAP hOldMap = (HBITMAP)SelectObject(hDCMem, hBitMap);

    //
    BitBlt(hDCMem, 0, 0, rect.right, rect.bottom, hDC, 0, 0, SRCCOPY);
    hBitMap = (HBITMAP)SelectObject(hDCMem, hOldMap);
    return hBitMap;
}