Drawing Text on the Desktop

This is a discussion on Drawing Text on the Desktop within the Windows Programming forums, part of the Platform Specific Boards category; Just wondering if anyone can suggest the best way to draw text on the desktop that is persistant. I.e. if ...

  1. #1
    Registered User dalek's Avatar
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    Drawing Text on the Desktop

    Just wondering if anyone can suggest the best way to draw text on the desktop that is persistant. I.e. if I draw text on the desktop using TextOut, the text will persist as long as it is not covered up. Of course this is expected, but in a normal app you would just process a WM_PAINT message to redraw the text, but how could one do this if the text is on the desktop? Perhaps using a timer to refresh it periodically?

    Any suggestions welcome.

  2. #2
    Registered User Codeplug's Avatar
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    >> Perhaps using a timer to refresh it periodically?
    That would work to some extent...

    You could create a transparent window that maintains itself at the bottom of the z-order - there's probably a better programatic solution though.

    However, this type of functionality is typically implemented using HTML and "active desktop".

    gg

  3. #3
    Registered User dalek's Avatar
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    Ah ok - cheers, it's just one of those things I had never thought of until someone asked me to write something like this.

    Thanks.

  4. #4
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    This should work:
    Code:
    while(true)
    {
      HDC DeskDC;
      RECT rc;
      rc.left = 0;
      rc.top = 0;
      rc.right = GetSystemMetrics(SM_CXSCREEN);
      rc.bottom = GetSystemMetrics(SM_CYSCREEN);
      DeskDC = GetDC(HWND_DESKTOP);
      SetBkMode(DeskDC, TRANSPARENT);
      DrawText(DeskDC, "Your text here", -1, &rc, DT_CENTER | DT_VCENTER | DT_EXPANDTABS);
    }

  5. #5
    Yes, my avatar is stolen anonytmouse's Avatar
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    Well, I thought you could use a transparent window to do this as suggested by Codeplug but there is one small issue.

    If you are going to draw directly on the desktop, I suggest you hook the SysListView desktop child and only paint when it receives a WM_PAINT.

    Anyway, here is the transparent window code:
    Code:
    /* Win 2000/XP+ only */
    #include <windows.h>
    
    #ifndef WS_EX_LAYERED
    #     define WS_EX_LAYERED 0x80000 
    #     define LWA_COLORKEY  1 
    #     define LWA_ALPHA     2 
    #endif
    
    
    void OnPaint(HWND hwnd, HDC hdc)
    {
    	RECT rc;
    
    	GetClientRect(hwnd, &rc);
    	SetTextColor(hdc, RGB(255,0,0));
    	DrawText(hdc, "Your text here", -1, &rc,
    	         DT_CENTER | DT_VCENTER | DT_EXPANDTABS | DT_SINGLELINE);
    }
    
    
    static LRESULT CALLBACK WndProc (HWND hwnd, UINT uMsg, WPARAM wParam, LPARAM lParam)
    {
    	switch (uMsg)
    	{
    		case WM_CREATE:
    			return 0;
    
    		case WM_DESTROY:
    			PostQuitMessage(0);
    			return 0;
    
    		case WM_PAINT:
    		{
    			PAINTSTRUCT ps;
    			HDC hdc;
    
    			hdc = BeginPaint(hwnd, &ps);
    			OnPaint(hwnd, hdc);
    			EndPaint(hwnd, &ps);
    			return 0;
    		}
    	}
    
    	return DefWindowProc(hwnd, uMsg, wParam, lParam);
    }
    
    
    int WINAPI WinMain(HINSTANCE hInstance, HINSTANCE hPrevInstance, LPSTR lpCmdLine, int nCmdShow)
    {
    	WNDCLASSEX wc = { 0 };
    	POINT pt      = { 0 };
    	HWND hwnd;
    	MSG Msg;
    	HRGN hrgn;
    	RECT rcClient, rcWnd, rcRgn;
    	HANDLE hDll;
    
    	wc.cbSize        = sizeof(WNDCLASSEX);
    	wc.style         = 0;
    	wc.lpfnWndProc   = WndProc;
    	wc.cbClsExtra    = 0;
    	wc.cbWndExtra    = 0;
    	wc.hInstance     = hInstance;
    	wc.hIcon         = NULL;
    	wc.hCursor       = LoadCursor(NULL, IDC_ARROW);
    	wc.hbrBackground = (HBRUSH) GetStockObject(WHITE_BRUSH);
    	wc.lpszMenuName  = NULL;
    	wc.lpszClassName = TEXT("TransparentDemo");
    	wc.hIconSm       = NULL;
    
    	if(!RegisterClassEx(&wc)) return 0;
    
    	hwnd = CreateWindowEx(WS_EX_LAYERED | WS_EX_TOOLWINDOW, TEXT("TransparentDemo"), NULL,
    	                      0, CW_USEDEFAULT, CW_USEDEFAULT, 240, 120,
    	                      NULL, NULL, hInstance, NULL);
    
    	/* Hide title bar */
    	ClientToScreen(hwnd, &pt);
    	GetWindowRect(hwnd, &rcWnd);
    	GetClientRect(hwnd, &rcClient); 
    
    	rcRgn.left   = pt.x - rcWnd.left;
    	rcRgn.top    = pt.y - rcWnd.top;
    	rcRgn.right  = rcRgn.left + rcClient.right;
    	rcRgn.bottom = rcRgn.top  + rcClient.bottom;
    
    	hrgn = CreateRectRgn(rcRgn.left, rcRgn.top, rcRgn.right, rcRgn.bottom); 
    	SetWindowRgn(hwnd, hrgn, FALSE);
    
    	ShowWindow(hwnd, nCmdShow);
    
    	/* Send to bottom */
    	SetWindowPos(hwnd, HWND_BOTTOM, 0, 0, 0, 0, SWP_NOMOVE | SWP_NOSIZE);
    
    	hDll = LoadLibrary(TEXT("user32"));
    
    	if (hDll)
    	{
    		typedef DWORD (WINAPI * PSLWA)(HWND, DWORD, BYTE, DWORD);
    		PSLWA pSetLayeredWindowAttributes;
    
    		pSetLayeredWindowAttributes = 
    	              (PSLWA) GetProcAddress(hDll,"SetLayeredWindowAttributes");
    
    		if (pSetLayeredWindowAttributes != NULL)
    		{
    			pSetLayeredWindowAttributes (hwnd, RGB(255,255,255), 0, LWA_COLORKEY);
    		}
    
    		FreeLibrary(hDll);
    	}
    
    	while(GetMessage(&Msg, NULL, 0, 0) > 0)
    	{
    		TranslateMessage(&Msg);
    		DispatchMessage(&Msg);
    	}
    
    	return Msg.wParam;
    }

  6. #6
    Registered User dalek's Avatar
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    Hey thanks - thats a cool way of doing it. I'll have a play with that code

  7. #7
    Yes, my avatar is stolen anonytmouse's Avatar
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