PrintWindow() only works sometimes

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Hi, I want to make a Screenshot of a CWnd and then Print it out. I already created some basic Code for testing purposes but if I'm actually printing it only works sometimes (on some Printers in combination with some PC's I'm printing from). What's always working is to directly draw a Rectangle to the Device Context but when I'm calling the "printWindow" It sometimes has no effect (it always returns true). I also don't think that its a driver problem of the PC because I never had any problems and I also tested it on 2 more Pc's.

So there Are 2 Scenarios when I'm printing:
1) I only see a Rectangle (white/transparent inside)
2) I see the Window and a Rectangle around it

In my Example I created a Basic MFC App (DialogBased) and just added a Button to Print the Window. I also created another Function to get the Default Printer Name but I dont think thats the cause so I din't uploaded it here.

Here is the Code:

C++

//Create Members
CDC pDC;
HDC hdc;

//Get Printer/Printer Settings
LPCSTR buffer = NULL;
GetDefaultPrinterName(buffer);
hdc = CreateDC(_T( "winspool" ), buffer, NULL, NULL);
pDC.Attach(hdc);

//Start Document Printing
pDC.StartDoc("test");
pDC.StartPage();

if (! ::PrintWindow(this->GetSafeHwnd(), pDC.GetSafeHdc(), PW_CLIENTONLY))
    AfxMessageBox("Error when calling \"PrintWindow()\"");

//Render Frame Rectangle
CRect WindowRect;
GetClientRect(WindowRect);
WindowRect.MoveToXY(0,0);
CBrush brush;
brush.CreateSolidBrush(RGB(0,0,0));
pDC.FrameRect(WindowRect,  &brush);

// Finish Printing
pDC.EndPage();
pDC.EndDoc();

Do you know what causes the problem or what could I do as an Workaround?

Posted 28-Jun-15 20:30pm

Michael Rampl

Updated 28-Jun-15 20:35pm

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Richard MacCutchan · Accepted Answer · 2015-06-28T21:56:00

Solution 1

See https://msdn.microsoft.com/en-us/library/windows/desktop/dd162869(v=vs.85).aspx[^]. This function sends a WM_PRINT message to the window in the function call, so it is that window's responsibility to do the actual rendering into the DC.

Posted 28-Jun-15 21:56pm

Richard MacCutchan

Comments

Michael Rampl 29-Jun-15 4:27am

thx for the response,
I tried but with the same result

PrintWindow(&pDC ,PW_CLIENTONLY)

Richard MacCutchan 29-Jun-15 9:23am

How do you think that will change anything? As I said, and the documentation explains, it is the receiving window that must do the rendering, it is not done by the system.

Michael Rampl 30-Jun-15 1:54am

sry i think i miss unterstood you,
yet now i dont handle any messages at all. All i did was creating a new mfc dialog based app, added a button with the function code from above and a function to get the default printer.
The rendering as it is in my Application, is done by the default mfc code, i haven't touched it at all so my guess was that it would "just run" with the default implementation.
The only Thing thats related to rendering in my Code is the OnPaint default mfc override.

void CPrintingTestDlg::OnPaint()
{
if (IsIconic())
{
CPaintDC dc(this); // device context for painting

SendMessage(WM_ICONERASEBKGND, reinterpret_cast(dc.GetSafeHdc()), 0);

// Center icon in client rectangle
int cxIcon = GetSystemMetrics(SM_CXICON);
int cyIcon = GetSystemMetrics(SM_CYICON);
CRect rect;
GetClientRect(&rect);
int x = (rect.Width() - cxIcon + 1) / 2;
int y = (rect.Height() - cyIcon + 1) / 2;

// Draw the icon
dc.DrawIcon(x, y, m_hIcon);
}
else
{
CDialogEx::OnPaint();
}
}

Richard MacCutchan 30-Jun-15 3:28am

You still need to handle the WM_PRINT message, the framework will not do it for you. You need to add a message map entry for this message, and write the implementation which displays the infomration on the DC.

Michael Rampl 30-Jun-15 4:21am

so you mean something like this?
http://stackoverflow.com/questions/12000458/how-to-handle-wm-print-message-in-a-cwnd-using-mfc

Richard MacCutchan 30-Jun-15 4:22am

Something like, yes.

Michael Rampl 30-Jun-15 5:19am

but in this case i would have to draw the cwnd completely by my self using gdi functions?

Richard MacCutchan 1-Jul-15 3:13am

Yes, that is how printing works in Windows. The only difference between displaying on a screen DC and a printer DC, is that in the printer case, you have to take account of the page size.