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. :)

>> 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

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.

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);
}

---

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;
}

---

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

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