Drawing Text on the Desktop

[dalek]

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.

[Codeplug]

>> 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

[dalek]

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.

[kristoffer]

This should work:

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);
}

[anonytmouse]

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:

/* 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;
}

[dalek]

Hey thanks - thats a cool way of doing it. I'll have a play with that code

[anonytmouse]

Also:
HOOK: http://www.angelcode.com/dev/desktopdraw/
OVERLAY: http://www.angelcode.com/dev/overlay/