Is it possible to attach another apps' window DC? (About Gdi handle table and objects)

sawerr

Hi I want to make a program that retrieves other windows' pixel values. First i made a default application which title name is "Untitled - NewWindow" and one more MFC project which is trying to draw to that window. The code is:

void CDeviceContextDlg::OnBnClickedButton1()
{
::EnumWindows(EnumWindowsProc, NULL);
}

BOOL CALLBACK EnumWindowsProc(HWND hwnd, LPARAM lParam)
{
if(hwnd == FindWindow(NULL,L"Untitled - NewWindow"))
{
HDC dc = GetDC(hwnd);
CDeviceContextDlg *dlg = (CDeviceContextDlg *)AfxGetMainWnd();
if((dlg->Clientdc.Attach(dc)))
{
dlg->Clientdc.SetBkColor(RGB(255,0,0));

	};
};
return TRUE;

}

It gives run-time error. I debugged it and in that line:

HDC dc = GetDC(hwnd);

In Debugger:

dc 0x53011041 {unused=??? } HDC__ *
unused CXX0030: Error: expression cannot be evaluated

Is it because process gdi handle table is process specific and it is impossible to get DC and draw another process' window? Or is there a way to draw another process' window or getpixel values? Thanks

CPallini

Maybe this [^] helps. :)

If the Lord God Almighty had consulted me before embarking upon the Creation, I would have recommended something simpler. -- Alfonso the Wise, 13th Century King of Castile.
This is going on my arrogant assumptions. You may have a superb reason why I'm completely wrong. -- Iain Clarke
[My articles]

Mark Salsbery

I tested this real quick, and it works fine for me. This example finds a NotePad instance and Blts the Notepad window to my window (note that "*pThis" in the callback == the HWND for the dialog window)...

BOOL CALLBACK CMFCTesterDlg::EnumWindowsProc(HWND hwnd, LPARAM lParam)
{
if(hwnd == ::FindWindow(NULL, L"Untitled - Notepad"))
{
CMFCTesterDlg *pThis = (CMFCTesterDlg *)lParam;
HWND hwnddest = *pThis;

	RECT rect;
	::GetWindowRect(hwnd, &rect);
	HDC dc = ::GetDCEx(hwnd, NULL, DCX\_WINDOW);
	HDC destdc = ::GetDC(hwnddest);
	::BitBlt(destdc, 0, 0, rect.right-rect.left, rect.bottom-rect.top, dc, 0, 0, SRCCOPY);
	::ReleaseDC(hwnddest, destdc);
	::ReleaseDC(hwnd, dc);
};
return TRUE;

}

void CMFCTesterDlg::OnOK()
{
::EnumWindows(&CMFCTesterDlg::EnumWindowsProc, (LPARAM)this);
}

Also, why the search within a search (FindWindow() within an EnumWindows() callback)?? :)

Mark Salsbery Microsoft MVP - Visual C++ :java:

sawerr

Thank you Mr.Mark Salsbery. Got it. :)

Rajesh R Subramanian

Just fixed the vote on this post of yours. :|

Nobody can give you wiser advice than yourself. - Cicero .·´¯`·->Rajesh<-·´¯`·. Microsoft MVP - Visual C++[^]

CPallini

Thank you friend. :rose: Anyway don't bother. Let's my personal troll having a touch of glory... :-D

If the Lord God Almighty had consulted me before embarking upon the Creation, I would have recommended something simpler. -- Alfonso the Wise, 13th Century King of Castile.
This is going on my arrogant assumptions. You may have a superb reason why I'm completely wrong. -- Iain Clarke
[My articles]

Rajesh R Subramanian

I am searching ebay for a device that would let you find and punch one troll at a time, with a folded fist, through the internet.

Nobody can give you wiser advice than yourself. - Cicero .·´¯`·->Rajesh<-·´¯`·. Microsoft MVP - Visual C++[^]

CPallini

Well, you can buy one (ore more) of these [^] and then proceed with voodoo ceremony. :laugh:

If the Lord God Almighty had consulted me before embarking upon the Creation, I would have recommended something simpler. -- Alfonso the Wise, 13th Century King of Castile.
This is going on my arrogant assumptions. You may have a superb reason why I'm completely wrong. -- Iain Clarke
[My articles]

Rajesh R Subramanian

:laugh:

Nobody can give you wiser advice than yourself. - Cicero .·´¯`·->Rajesh<-·´¯`·. Microsoft MVP - Visual C++[^]