How to block resizing after a double-click on a dialog window's top or bottom edges in Windows 10?

Question

I'm coding a customized popup window with C++ using Win32. The condition for this popup window is that it can be only resized from the bottom down. The following is the implementation of such restriction:

RECT rcInitialWindowRectangle = {0};

//The dialog has WS_THICKFRAME style

LRESULT CALLBACK DlgWndProc(HWND hDlg, UINT message, WPARAM wParam, LPARAM lParam)
{
    case WM_INITDIALOG:
        {
            //Set minimum window size
            ::GetWindowRect(hDlg, &rcInitialWindowRectangle);
        }
        break;

    case WM_SIZING:
        {
            //Restrict sizing on all sides but bottom
            if(wParam != WMSZ_BOTTOM)
            {
                RECT* pRcWnd = (RECT*)lParam;

                //Preserve all sides but bottom
                int b = pRcWnd->bottom;
                *pRcWnd = rcInitialWindowRectangle;
                pRcWnd->bottom = b;

                return TRUE;
            }
        }
        break;

    case WM_GETMINMAXINFO:
        {
            //The following is needed to restrict minimum window size
            int w = rcInitialWindowRectangle.right - rcInitialWindowRectangle.left;
            if(w != 0)
            {
                MINMAXINFO* pMMI = (MINMAXINFO*)lParam;

                pMMI->ptMinTrackSize.x = w;
                pMMI->ptMinTrackSize.y = rcInitialWindowRectangle.bottom - rcInitialWindowRectangle.top;

                pMMI->ptMaxTrackSize.x = w;
            }
        }
        break;

    case WM_NCHITTEST:
        {
            //The following is needed to display correct cursor for resizing
            POINT pnt = {GET_X_LPARAM(lParam), GET_Y_LPARAM(lParam)};

            RECT rcWnd;
            ::GetWindowRect(hDlg, &rcWnd);

            //L, T, R, B
            RECT rcBtm = {rcInitialWindowRectangle.left, 
                rcWnd.bottom - 16,  //Some arbitrary border 
                rcInitialWindowRectangle.right,
                rcWnd.bottom};

            return ::PtInRect(&rcBtm, pnt) ? HTNOWHERE : HTBORDER;
        }
        break;


    return 0;
}

So this works except one thing. On Windows 10, there's evidently a new feature -- when someone double-clicks on the bottom (or top) edge of a window -- here's an example with Notepad so that you can try:

that window is resized (stretched) to the top and bottom of the screen (akin to maximization, but only vertically.)

So my question is how do I block this double-click resizing? (In my case the top of the popup window should not move.)

PS. My first instinct was to block all double-clicks on the window's edge, but then I thought that maybe there's a less barbaric way to achieve this?

Answer 1

You are already handling WM_NCHITTEST. Handle WM_NCLBUTTONDBLCLK and don't forward to DefWindowProc unless the hit test (in wParam) indicates the lower frame.

Answer 2

here's the workaround that seems to work for me. It is not really about blocking the double-clicks. (Apart from subclassing the WndProc of a dialog box, which I haven't tried, I failed to block that double-click effect in DlgProc alone.) My workaround presented below is to achor the top of the popup window and let it drop down to the bottom of the screen, if the user who double-clicks the bottom border wants similar stuff to happen.

Since this does not answer my original question, I won't mark it as such.

//Add this case statement to my original code

case WM_WINDOWPOSCHANGING:
    {
        WINDOWPOS* pWP = (WINDOWPOS*)lParam;
        if(!(pWP->flags & (SWP_NOMOVE | SWP_NOSIZE)))
        {
            int w = rcInitialWindowRectangle.right - rcInitialWindowRectangle.left;
            if(w > 0)
            {
                //Anchor the top of the popup window
                pWP->x = rcInitialWindowRectangle.left;
                pWP->y = rcInitialWindowRectangle.top;

                pWP->cx = w;

                int h = pWP->cy;

                //Make sure that the height fits the screen
                POINT pnt = {pWP->x, pWP->y};
                MONITORINFO mi = {0};
                mi.cbSize = sizeof(mi);
                if(::GetMonitorInfo(::MonitorFromPoint(pnt, MONITOR_DEFAULTTONEAREST), &mi))
                {
                    if(pWP->y + h > mi.rcWork.bottom)
                    {
                        int nMinDefaultH = rcInitialWindowRectangle.bottom - 
                            rcInitialWindowRectangle.top;

                        int nAh = mi.rcWork.bottom - y;
                        if(nAh >= nMinDefaultH)
                            h = nAh;
                        else
                            h = nMinDefaultH;
                    }
                }

                pWP->cy = h;
            }
        }
    }
    break;