为什么无法间接显示,g_hwnd为窗口句柄,直接把tmpdc用bibl到g_hdc都可以显示，哪里出错了呢
g_hWnd=hwnd;
g_hDC=GetDC(hwnd);
hMDC=CreateCompatibleDC(g_hDC);
tmpDC=CreateCompatibleDC(g_hDC);

ShowWindow (hwnd, iCmdShow) ;
UpdateWindow (hwnd) ;

hBit1=(HBITMAP)LoadImage(hInstance,"1.bmp",IMAGE_BITMAP,600,400,LR_LOADFROMFILE|LR_CREATEDIBSECTION);


SelectObject(hMDC,CreateCompatibleBitmap(g_hDC,600,400));

hOldBit1=(HBITMAP)SelectObject(tmpDC,hBit1);
BitBlt(hMDC,0,0,600,400,tmpDC,0,0,SRCCOPY);
SelectObject(hMDC,hOldBit1);


BitBlt(g_hDC,0,0,600,400,hMDC,0,0,SRCCOPY);
ReleaseDC(hwnd,g_hDC);