DC is not pointing to my window!

This is a discussion on DC is not pointing to my window! within the Windows Programming forums, part of the Platform Specific Boards category; I got a DC setup like this: Code: HDC hdcMainWin = GetDC(MainWindow); and instead of pointing to the client area ...

  1. #1
    Banned frenchfry164's Avatar
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    DC is not pointing to my window!

    I got a DC setup like this:
    Code:
    HDC hdcMainWin = GetDC(MainWindow);
    and instead of pointing to the client area of MainWindow, it goes to the top-left corner of the screen.

    I've included the .exe file to demonstrate.
    Attached Files Attached Files

  2. #2
    &TH of undefined behavior Fordy's Avatar
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    5,789
    More likely its an error with your code.

    But as you posted the exe, there's no way to suggest anything

  3. #3
    Banned frenchfry164's Avatar
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    Here is how I am creating the window, the loop, and the creation of the DC.

    Code:
    HWND MainWindow;
    ...
    int WINAPI WinMain(HINSTANCE hInstance, HINSTANCE, LPSTR, int nCmdShow)
    {
    	{
    		WNDCLASS wc;
    		wc.cbClsExtra = 0;
    		wc.cbWndExtra = 0;
    		wc.hbrBackground = (HBRUSH)COLOR_WINDOW;
    		wc.hCursor = LoadCursor(NULL, IDC_ARROW);
    		wc.hIcon = LoadIcon(NULL, IDI_APPLICATION);
    		wc.hInstance = hInstance;
    		wc.lpfnWndProc = MainWndProc;
    		wc.lpszClassName = "TED MainWindow";
    		wc.lpszMenuName = NULL;
    		wc.style = 0;
    
    		if (!RegisterClass(&wc))
    		{
    			MessageBox(NULL, "Error registering window class!", "Error", MB_OK);
    			return 1;
    		}
    	}
    
    	if (!CreateWindowEx(0, "TED MainWindow", 
    		"GDI Tile Engine Demo - Main Window", 
    		WS_OVERLAPPED | WS_VISIBLE | WS_MINIMIZEBOX | WS_SYSMENU,
    		CW_USEDEFAULT,	CW_USEDEFAULT,	640, 480, NULL, NULL, hInstance,
    		NULL))
    	{
    		MessageBox(NULL, "Error creating main window!", "Error", MB_OK);
    		return 1;
    	}
    
    	MSG msg;
            HDC hdcMainWin = GetDC(MainWindow);
    	HBITMAP hbmBall = LoadBitmap(hInstance, MAKEINTRESOURCE(IDB_BITMAP1));
    
    
       while (TRUE)
    	{
    		if (PeekMessage(&msg, NULL, 0, 0, PM_REMOVE))
    		{
    			if (msg.message != WM_QUIT)
    			{
    				TranslateMessage(&msg);
    				DispatchMessage(&msg);
    			}
    			else
    				break;
    		}
    			tempX ++;
    			tempY ++;
    			graphics.BeginFrame(hdcMainWin);
    			graphics.TransBlit(hbmBall, tempX, tempY);
    			graphics.EndFrame();
    	}
            ReleaseDC(MainWindow, hdcMainWin);
    	return msg.wParam;
    }

  4. #4
    Carnivore ('-'v) Hunter2's Avatar
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    May 2002
    Posts
    2,879
    Your problem is that MainWindow is null. GetDC(NULL) gives you a HDC to the screen, not the window. Try this instead:
    Code:
    MainWindow = CreateWindowEx(0, "TED MainWindow", 
    		"GDI Tile Engine Demo - Main Window", 
    		WS_OVERLAPPED | WS_VISIBLE | WS_MINIMIZEBOX | WS_SYSMENU,
    		CW_USEDEFAULT,	CW_USEDEFAULT,	640, 480, NULL, NULL, hInstance,
    		NULL);
    if(!MainWindow)
    {
       //stuff
    }
    That way you actually get the handle to the window
    Just Google It. √

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