Question

I have a window, which I SetWindowPos(window, HWND_TOP, 0, 0, GetSystemMetrics(SM_CXSCREEN), GetSystemMetrics(SM_CYSCREEN), SWP_FRAMECHANGED);

It covers the whole screen, ok, but it takes a while (0.5 sec) to cover the taskbar as well.

Is there a way to come over the taskbar immediately? I found that setting HWND_TOPMOST does it immediately, but it stays above all the other windows, even if I switch the app – this is something I don’t want. Also, if I first hide the window and then show it, it somehow forces the window to redraw and covers the taskbar immediately, but it flickers (because of the hiding). Is there another way?

Answer 1

Edit 2. There is even a better way for doing fullscreen, the chromium way, source taken from here:

http://src.chromium.org/viewvc/chrome/trunk/src/ui/views/win/fullscreen_handler.cc?revision=HEAD&view=markup

void FullscreenHandler::SetFullscreenImpl(bool fullscreen, bool for_metro) {
  ScopedFullscreenVisibility visibility(hwnd_);

  // Save current window state if not already fullscreen.
  if (!fullscreen_) {
    // Save current window information.  We force the window into restored mode
    // before going fullscreen because Windows doesn't seem to hide the
    // taskbar if the window is in the maximized state.
    saved_window_info_.maximized = !!::IsZoomed(hwnd_);
    if (saved_window_info_.maximized)
      ::SendMessage(hwnd_, WM_SYSCOMMAND, SC_RESTORE, 0);
    saved_window_info_.style = GetWindowLong(hwnd_, GWL_STYLE);
    saved_window_info_.ex_style = GetWindowLong(hwnd_, GWL_EXSTYLE);
    GetWindowRect(hwnd_, &saved_window_info_.window_rect);
  }

  fullscreen_ = fullscreen;

  if (fullscreen_) {
    // Set new window style and size.
    SetWindowLong(hwnd_, GWL_STYLE,
                  saved_window_info_.style & ~(WS_CAPTION | WS_THICKFRAME));
    SetWindowLong(hwnd_, GWL_EXSTYLE,
                  saved_window_info_.ex_style & ~(WS_EX_DLGMODALFRAME |
                  WS_EX_WINDOWEDGE | WS_EX_CLIENTEDGE | WS_EX_STATICEDGE));

    // On expand, if we're given a window_rect, grow to it, otherwise do
    // not resize.
    if (!for_metro) {
      MONITORINFO monitor_info;
      monitor_info.cbSize = sizeof(monitor_info);
      GetMonitorInfo(MonitorFromWindow(hwnd_, MONITOR_DEFAULTTONEAREST),
                     &monitor_info);
      gfx::Rect window_rect(monitor_info.rcMonitor);
      SetWindowPos(hwnd_, NULL, window_rect.x(), window_rect.y(),
                   window_rect.width(), window_rect.height(),
                   SWP_NOZORDER | SWP_NOACTIVATE | SWP_FRAMECHANGED);
    }
  } else {
    // Reset original window style and size.  The multiple window size/moves
    // here are ugly, but if SetWindowPos() doesn't redraw, the taskbar won't be
    // repainted.  Better-looking methods welcome.
    SetWindowLong(hwnd_, GWL_STYLE, saved_window_info_.style);
    SetWindowLong(hwnd_, GWL_EXSTYLE, saved_window_info_.ex_style);

    if (!for_metro) {
      // On restore, resize to the previous saved rect size.
      gfx::Rect new_rect(saved_window_info_.window_rect);
      SetWindowPos(hwnd_, NULL, new_rect.x(), new_rect.y(),
                   new_rect.width(), new_rect.height(),
                   SWP_NOZORDER | SWP_NOACTIVATE | SWP_FRAMECHANGED);
    }
    if (saved_window_info_.maximized)
      ::SendMessage(hwnd_, WM_SYSCOMMAND, SC_MAXIMIZE, 0);
  }
}

Edit.
It is probably better to create a fullscreen window as BrendanMcK pointed it out in a comment to this answer, see this link: http://blogs.msdn.com/b/oldnewthing/archive/2005/05/05/414910.aspx (“How do I cover the taskbar with a fullscreen window?”)

The new code using the link above would be:

HWND CreateFullscreenWindow(HWND hwnd)
{
 HMONITOR hmon = MonitorFromWindow(hwnd,
                                   MONITOR_DEFAULTTONEAREST);
 MONITORINFO mi = { sizeof(mi) };
 if (!GetMonitorInfo(hmon, &mi)) return NULL;
 return CreateWindow(TEXT("static"),
       TEXT("something interesting might go here"),
       WS_POPUP | WS_VISIBLE,
       mi.rcMonitor.left,
       mi.rcMonitor.top,
       mi.rcMonitor.right - mi.rcMonitor.left,
       mi.rcMonitor.bottom - mi.rcMonitor.top,
       hwnd, NULL, g_hinst, 0);
}

---

Old answer below – do not use it, stays only for the record on how NOT to do this.

You have to hide taskbar and menubar to see fullscreen immediately.

Here is the code (uses WTL), call SetFullScreen(true) to go into full screen mode:

template <class T, bool t_bHasSip = true>
class CFullScreenFrame
{
public:
    bool m_fullscreen;
    LONG m_windowstyles;
    WINDOWPLACEMENT m_windowplacement;

    CFullScreenFrame() 
        :
        m_fullscreen(false),
        m_windowstyles(0)
    { }

    void SetFullScreen(bool fullscreen)
    {
        ShowTaskBar(!fullscreen);

        T* pT = static_cast<T*>(this);

        if (fullscreen) {
            if (!m_fullscreen) {
                m_windowstyles = pT->GetWindowLongW(GWL_STYLE);
                pT->GetWindowPlacement(&m_windowplacement);
            }

        }

        // SM_CXSCREEN gives primary monitor, for multiple monitors use SM_CXVIRTUALSCREEN.
        RECT fullrect = { 0 };              
        SetRect(&fullrect, 0, 0, GetSystemMetrics(SM_CXSCREEN), GetSystemMetrics(SM_CYSCREEN));

        WINDOWPLACEMENT newplacement = m_windowplacement;
        newplacement.showCmd = SW_SHOWNORMAL;
        newplacement.rcNormalPosition = fullrect;

        if (fullscreen) {
            pT->SetWindowPlacement(&newplacement);
            pT->SetWindowLongW(GWL_STYLE,  WS_VISIBLE);
            pT->UpdateWindow();
        } else {
            if (m_fullscreen) {
                pT->SetWindowPlacement(&m_windowplacement);
                pT->SetWindowLongW(GWL_STYLE, m_windowstyles);
                pT->UpdateWindow();
            }
        }

        m_fullscreen = fullscreen;
    }

    void ShowTaskBar(bool show)
    {
        HWND taskbar = FindWindow(_T("Shell_TrayWnd"), NULL);
        HWND start = FindWindow(_T("Button"), NULL);

        if (taskbar != NULL) {
            ShowWindow(taskbar, show ? SW_SHOW : SW_HIDE);
            UpdateWindow(taskbar);
        }
        if (start != NULL) { 
            // Vista
            ShowWindow(start, show ? SW_SHOW : SW_HIDE);
            UpdateWindow(start);
        }       
    }
};

You also have to add some code to WM_CLOSE message:

case WM_CLOSE:
    ShowTaskBar(true);

There is one caveat with this solution, if your application crashes or is killed through task manager, then user losses taskbar on his system permanently! (unless he runs your application again, goes into fullscreen and exits, then he will see the taskbar again).

Earlier in my answer I pointed to “atlwince.h” but that function worked only on Windows CE, the one I pasted above works fine with XP, Vista and 7.