Pin window to desktop / Glue window to desktop / "Always-on-bottom" window

Question

I'm working on a basic desktop app in C++ / Win32.

My goal right now is to create a basic "sticky note" app that would be pinned / glued to the desktop, i.e always in front of the desktop but always behind of any other application. Really a personal project there, just to fight my bad memory and have my tasks/notes always visible on the desktop so I couldn't miss them when starting the computer & so on.

The behaviour I'm aiming for would be similar to Stardock Fences ("kind of" because I'm not going to store any desktop icon in there, but you hopefully get the idea)

I started with the sample code from the Get Started with Win32 and C++ docs to have the most basic Win32 minimal window setup.

What I got so far :

1. I managed to keep my window on bottom of every other app and in front of the desktop by calling SetWindowPos in the window procedure (WindowProc), when handling the event WM_SETFOCUS (I first tried with the event WM_WINDOWPOSCHANGING as suggested in this answer but this resulted in an annoying flickering when dragging the window).

case WM_SETFOCUS:
        SetWindowPos(hwnd, HWND_BOTTOM, 0, 0, 0, 0, SWP_NOSIZE | SWP_NOMOVE);
        return 0;

2. The problem : my window stays in front of the desktop, except when I click on the "Show Desktop" button in the taskbar (or hit the Windows + D shortcut). As I often use this shortcut myself, I'd like my window to stay over the desktop no matter what.
3. A not-satisfying-enough-but-still-something I managed to do is to bring back my window in front of the desktop when clicking on any other window after hitting Windows + D (this mostly makes sense with multiple monitors, as opening a random app on the first one for example, will toggle back my own app in front of the desktop on another screen). I could do this using this time the event WM_SIZE and calling ShowWindow then SetWindowPos, still in the WindowProc

case WM_SIZE:
        ShowWindow(hwnd, SW_SHOWNORMAL);
        SetWindowPos(hwnd, HWND_BOTTOM, 0, 0, 0, 0, SWP_NOSIZE | SWP_NOMOVE);
        return 0;

Not ideal though, as I'd really want my app to always remain in front of the desktop and "survive" to the Show Desktop action.

What I tried :

I checked out those answers but couldn't figure out how to achieve what I want.

1. How to make 'always-on-bottom'-window
2. Window “on desktop” : Note on this one, I tried the trick with SetParent like this in the wWinMain

HWND desktop = FindWindow(L"ProgMan", L"Program Manager");
if (desktop == NULL)
{
    return 0;
}

ShowWindow(hwnd, nCmdShow);
SetParent(hwnd, desktop);

However, my app isn't visible at all anymore with this, even though the FindWindow didn't return NULL but an actual handle.

3. Make aplication always on Bottom (pinned to desktop, behind all other apps) in C++/WinAPI [duplicate]
4. Disable Minimize, Maximize, Close buttons in Win32 I tried those to "intercept" the Show Desktop event but it seems this event doesn't get fired with the Show Desktop action.

Did I miss something ?

Answer 1

As @JonathanPotter pointed out, when hitting Windows + D or the Show Desktop button, the event WM_WINDOWPOSCHANGING gets fired, and the window gets moved to -32 000, -32 000 (its size also gets changed)

NOTE : a window without the style WS_MINIMIZEBOX seems not receiving WINDOWPOSCHANGING event when hitting Windows + D. Thus, no -32 000 coordinates detection in that case... Also noticed the same issue when using the ex style WS_EX_TOOLWINDOW (as this one gets rid of the minimize box, even if you set the style flag WS_MINIMIZEBOX). Didn't find a solution for that case, so I'm sticking to an overlapped window.

To prevent this movement, just set the flags SWP_NOMOVE and SWP_NOSIZE on the WINDOWPOS structure passed in the lParam

So as a final result, to achieve the wanted behaviour (i.e always behind every other window but always in front of the desktop), the only needed code to add to the doc's sample is the following, placed in the window procedure WindowProc's switch statement :

EDIT : the best place to force the Z order with HWND_BOTTOM thus ensuring the window is always on bottom is also in the WM_WINDOWPOSCHANGING event. Indeed, calling SetWindowPos to force it in the WM_SIZE event when dragging the window over, as I was doing previously, causes some flickering on the window when resizing it, whereas no flickering occurs when setting directly the hwndInsertAfter property of the WINDOWPOS structure in WM_WINDOWPOSCHANGING.

case WM_WINDOWPOSCHANGING:
{
    WINDOWPOS* pos = (WINDOWPOS*)lParam;
    // Show desktop (Windows + D) results in the window moved to -32000, -32000 and size changed
    if (pos->x == -32000) {
        // Set the flags to prevent this and "survive" to the desktop toggle
        pos->flags |= SWP_NOMOVE | SWP_NOSIZE;
    }
    // Also force the z order to ensure the window is always on bottom
    pos->hwndInsertAfter = HWND_BOTTOM;
    return 0;
}