1 files changed, 432 insertions, 0 deletions
diff --git a/widget/windows/nsWindowTaskbarConcealer.cpp b/widget/windows/nsWindowTaskbarConcealer.cpp
new file mode 100644
index 0000000000..19c58e871b
--- /dev/null
+++ b/widget/windows/nsWindowTaskbarConcealer.cpp
@@ -0,0 +1,432 @@
+/* -*- Mode: C++; tab-width: 2; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+#include "nsWindowTaskbarConcealer.h"
+
+#include "nsIWinTaskbar.h"
+#define NS_TASKBAR_CONTRACTID "@mozilla.org/windows-taskbar;1"
+
+#include "mozilla/Logging.h"
+
+/**
+ * TaskbarConcealerImpl
+ *
+ * Implement Windows-fullscreen marking.
+ *
+ * nsWindow::TaskbarConcealer implements logic determining _whether_ to tell
+ * Windows that a given window is fullscreen. TaskbarConcealerImpl performs the
+ * platform-specific work of actually communicating that fact to Windows.
+ *
+ * (This object is not persistent; it's constructed on the stack when needed.)
+ */
+struct TaskbarConcealerImpl {
+  void MarkAsHidingTaskbar(HWND aWnd, bool aMark);
+
+ private:
+  nsCOMPtr<nsIWinTaskbar> mTaskbarInfo;
+};
+
+/**
+ * nsWindow::TaskbarConcealer
+ *
+ * Issue taskbar-hide requests to the OS as needed.
+ */
+
+/*
+  Per MSDN [0], one should mark and unmark fullscreen windows via the
+  ITaskbarList2::MarkFullscreenWindow method. Unfortunately, Windows pays less
+  attention to this than one might prefer -- in particular, it typically fails
+  to show the taskbar when switching focus from a window marked as fullscreen to
+  one not thus marked. [1]
+
+  Experimentation has (so far) suggested that its behavior is reasonable when
+  switching between multiple monitors, or between a set of windows which are all
+  from different processes [2]. This leaves us to handle the same-monitor, same-
+  process case.
+
+  Rather than do anything subtle here, we take the blanket approach of simply
+  listening for every potentially-relevant state change, and then explicitly
+  marking or unmarking every potentially-visible toplevel window.
+
+  ----
+
+  [0] Relevant link:
+      https://docs.microsoft.com/en-us/windows/win32/api/shobjidl_core/nf-shobjidl_core-itaskbarlist2-markfullscreenwindow
+
+      The "NonRudeHWND" property described therein doesn't help with anything
+      in this comment, unfortunately. (See its use in MarkAsHidingTaskbar for
+      more details.)
+
+  [1] This is an oversimplification; Windows' actual behavior here is...
+      complicated. See bug 1732517 comment 6 for some examples.
+
+  [2] A comment in Chromium asserts that this is actually different threads. For
+      us, of course, that makes no difference.
+      https://github.com/chromium/chromium/blob/2b822268bd3/ui/views/win/hwnd_message_handler.cc#L1342
+*/
+
+/**************************************************************
+ *
+ * SECTION: TaskbarConcealer utilities
+ *
+ **************************************************************/
+
+static mozilla::LazyLogModule sTaskbarConcealerLog("TaskbarConcealer");
+
+// Map of all relevant Gecko windows, along with the monitor on which each
+// window was last known to be located.
+/* static */
+nsTHashMap<HWND, HMONITOR> nsWindow::TaskbarConcealer::sKnownWindows;
+
+// Preference for changes associated with bug 1732517. When false, revert to the
+// previous simple behavior of "Firefox fullscreen == Windows fullscreen".
+//
+// For simplicity-of-implementation's sake, changes to this pref require a
+// restart of Firefox to take effect.
+static bool UseAlternateFullscreenHeuristics() {
+  static const bool val =
+      StaticPrefs::widget_windows_alternate_fullscreen_heuristics();
+  return val;
+}
+
+// Returns Nothing if the window in question is irrelevant (for any reason),
+// or Some(the window's current state) otherwise.
+/* static */
+Maybe<nsWindow::TaskbarConcealer::WindowState>
+nsWindow::TaskbarConcealer::GetWindowState(HWND aWnd) {
+  // Classical Win32 visibility conditions.
+  if (!::IsWindowVisible(aWnd)) {
+    return Nothing();
+  }
+  if (::IsIconic(aWnd)) {
+    return Nothing();
+  }
+
+  // Non-nsWindow windows associated with this thread may include file dialogs
+  // and IME input popups.
+  nsWindow* pWin = WinUtils::GetNSWindowPtr(aWnd);
+  if (!pWin) {
+    return Nothing();
+  }
+
+  // nsWindows of other window-classes include tooltips and drop-shadow-bearing
+  // menus.
+  if (pWin->mWindowType != eWindowType_toplevel) {
+    return Nothing();
+  }
+
+  // Cloaked windows are (presumably) on a different virtual desktop.
+  // https://devblogs.microsoft.com/oldnewthing/20200302-00/?p=103507
+  if (pWin->mIsCloaked) {
+    return Nothing();
+  }
+
+  return Some(
+      WindowState{::MonitorFromWindow(aWnd, MONITOR_DEFAULTTONULL),
+                  pWin->mFrameState->GetSizeMode() == nsSizeMode_Fullscreen});
+}
+
+/**************************************************************
+ *
+ * SECTION: TaskbarConcealer::UpdateAllState
+ *
+ **************************************************************/
+
+// Update all Windows-fullscreen-marking state and internal caches to represent
+// the current state of the system.
+/* static */
+void nsWindow::TaskbarConcealer::UpdateAllState(
+    HWND destroyedHwnd /* = nullptr */
+) {
+  // sKnownWindows is otherwise-unprotected shared state
+  MOZ_ASSERT(NS_IsMainThread(),
+             "TaskbarConcealer can only be used from the main thread!");
+
+  if (MOZ_LOG_TEST(sTaskbarConcealerLog, LogLevel::Info)) {
+    static size_t sLogCounter = 0;
+    MOZ_LOG(sTaskbarConcealerLog, LogLevel::Info,
+            ("Calling UpdateAllState() for the %zuth time", sLogCounter++));
+
+    MOZ_LOG(sTaskbarConcealerLog, LogLevel::Info, ("Last known state:"));
+    if (sKnownWindows.IsEmpty()) {
+      MOZ_LOG(sTaskbarConcealerLog, LogLevel::Info,
+              ("  none (no windows known)"));
+    } else {
+      for (const auto& entry : sKnownWindows) {
+        MOZ_LOG(
+            sTaskbarConcealerLog, LogLevel::Info,
+            ("  window %p was on monitor %p", entry.GetKey(), entry.GetData()));
+      }
+    }
+  }
+
+  // Array of all our potentially-relevant HWNDs, in Z-order (topmost first),
+  // along with their associated relevant state.
+  struct Item {
+    HWND hwnd;
+    HMONITOR monitor;
+    bool isGkFullscreen;
+  };
+  const nsTArray<Item> windows = [&] {
+    nsTArray<Item> windows;
+
+    // USE OF UNDOCUMENTED BEHAVIOR: The EnumWindows family of functions
+    // enumerates windows in Z-order, topmost first. (This has been true since
+    // at least Windows 2000, and possibly since Windows 3.0.)
+    //
+    // It's necessarily unreliable if windows are reordered while being
+    // enumerated; but in that case we'll get a message informing us of that
+    // fact, and can redo our state-calculations then.
+    //
+    // There exists no documented interface to acquire this information (other
+    // than ::GetWindow(), which is racy).
+    mozilla::EnumerateThreadWindows([&](HWND hwnd) {
+      // Depending on details of window-destruction that probably shouldn't be
+      // relied on, this HWND may or may not still be in the window list.
+      // Pretend it's not.
+      if (hwnd == destroyedHwnd) {
+        return;
+      }
+
+      const auto maybeState = GetWindowState(hwnd);
+      if (!maybeState) {
+        return;
+      }
+      const WindowState& state = *maybeState;
+
+      windows.AppendElement(Item{.hwnd = hwnd,
+                                 .monitor = state.monitor,
+                                 .isGkFullscreen = state.isGkFullscreen});
+    });
+
+    return windows;
+  }();
+
+  // Relevant monitors are exactly those with relevant windows.
+  const nsTHashSet<HMONITOR> relevantMonitors = [&]() {
+    nsTHashSet<HMONITOR> relevantMonitors;
+    for (const Item& item : windows) {
+      relevantMonitors.Insert(item.monitor);
+    }
+    return relevantMonitors;
+  }();
+
+  // Update the cached mapping from windows to monitors. (This is only used as
+  // an optimization in TaskbarConcealer::OnWindowPosChanged().)
+  sKnownWindows.Clear();
+  for (const Item& item : windows) {
+    MOZ_LOG(
+        sTaskbarConcealerLog, LogLevel::Debug,
+        ("Found relevant window %p on monitor %p", item.hwnd, item.monitor));
+    sKnownWindows.InsertOrUpdate(item.hwnd, item.monitor);
+  }
+
+  // Auxiliary function. Does what it says on the tin.
+  const auto FindUppermostWindowOn = [&windows](HMONITOR aMonitor) -> HWND {
+    for (const Item& item : windows) {
+      if (item.monitor == aMonitor) {
+        MOZ_LOG(sTaskbarConcealerLog, LogLevel::Info,
+                ("on monitor %p, uppermost relevant HWND is %p", aMonitor,
+                 item.hwnd));
+        return item.hwnd;
+      }
+    }
+
+    // This should never happen, since we're drawing our monitor-set from the
+    // set of relevant windows.
+    MOZ_LOG(sTaskbarConcealerLog, LogLevel::Warning,
+            ("on monitor %p, no relevant windows were found", aMonitor));
+    return nullptr;
+  };
+
+  TaskbarConcealerImpl impl;
+
+  // Mark all relevant windows as not hiding the taskbar, unless they're both
+  // Gecko-fullscreen and the uppermost relevant window on their monitor.
+  for (HMONITOR monitor : relevantMonitors) {
+    const HWND topmost = FindUppermostWindowOn(monitor);
+
+    for (const Item& item : windows) {
+      if (item.monitor != monitor) continue;
+      impl.MarkAsHidingTaskbar(item.hwnd,
+                               item.isGkFullscreen && item.hwnd == topmost);
+    }
+  }
+}  // nsWindow::TaskbarConcealer::UpdateAllState()
+
+// Mark this window as requesting to occlude the taskbar. (The caller is
+// responsible for keeping any local state up-to-date.)
+void TaskbarConcealerImpl::MarkAsHidingTaskbar(HWND aWnd, bool aMark) {
+  // USE OF UNDOCUMENTED BEHAVIOR:
+  //
+  // `MarkFullscreenWindow` is documented not to be sufficient. It will indeed
+  // cause a window to be treated as fullscreen; but, in its absence, Windows
+  // will also use explicitly undocumented heuristics to determine whether or
+  // not to treat a given window as full-screen.
+  //
+  // In Windows 8.1 and later, these heuristics don't seem to apply to us.
+  // However, in Windows 7, they do -- they determine that our fullscreen
+  // windows are, indeed, fullscreen. (That this is technically correct is of
+  // little importance, given that Windows then goes on to do the wrong thing
+  // with that knowledge.)
+  //
+  // Fortunately, `MarkFullscreenWindow` does have a converse: the `NonRudeHWND`
+  // window property. A window with this property set will not be treated as
+  // fullscreen.
+  //
+  // ===
+  //
+  // DIFFERENCE FROM DOCUMENTED BEHAVIOR:
+  //
+  // The documentation, as it was at the time of writing, is archived at:
+  // https://web.archive.org/web/20211223073250/https://docs.microsoft.com/en-us/windows/win32/api/shobjidl_core/nf-shobjidl_core-itaskbarlist2-markfullscreenwindow
+  //
+  // The most relevant paragraph follows:
+  //
+  // > **Since Windows 7**, call `SetProp(hwnd, L”NonRudeHWND”,
+  // > reinterpret_cast<HANDLE>(TRUE))` before showing a window to indicate to
+  // > the Shell that the window should not be treated as full-screen.
+  //
+  // The key words in that paragraph are "before showing a window". On Windows 7
+  // this has no particular effect, but it completely changes the behavior on
+  // Windows 8.1 and Windows 10 -- if `NonRudeHWND` is set on a window before it
+  // is shown, that window will not be treated as fullscreen **even if the
+  // property is later removed!**
+  //
+  // `NonRudeHWND` isn't actually documented to do anything at all if it's set
+  // after the window has already been shown. That it seems to do exactly what
+  // we need on Windows 7 -- prevent a window from being detected as fullscreen
+  // while it's set, and only then -- is a stroke of fortune.
+
+  static const bool kUseWin7MarkingHack = [&] {
+    switch (StaticPrefs::widget_windows_fullscreen_marking_workaround()) {
+      case -1:
+        return false;
+      case 1:
+        return true;
+      default:
+        // The behavior on Windows 8 is not known. Hopefully there are no
+        // side effects there.
+        return !mozilla::IsWin8Point1OrLater();
+    }
+  }();
+
+  if (kUseWin7MarkingHack) {
+    constexpr static LPCWSTR kPropName = L"NonRudeHWND";
+    if (aMark) {
+      ::RemovePropW(aWnd, kPropName);
+    } else {
+      ::SetPropW(aWnd, kPropName, reinterpret_cast<HANDLE>(TRUE));
+    }
+  }
+
+  const char* const sMark = aMark ? "true" : "false";
+
+  if (!mTaskbarInfo) {
+    mTaskbarInfo = do_GetService(NS_TASKBAR_CONTRACTID);
+
+    if (!mTaskbarInfo) {
+      MOZ_LOG(
+          sTaskbarConcealerLog, LogLevel::Warning,
+          ("could not acquire IWinTaskbar (aWnd %p, aMark %s)", aWnd, sMark));
+      return;
+    }
+  }
+
+  MOZ_LOG(sTaskbarConcealerLog, LogLevel::Info,
+          ("Calling PrepareFullScreenHWND(%p, %s)", aWnd, sMark));
+
+  const nsresult hr = mTaskbarInfo->PrepareFullScreenHWND(aWnd, aMark);
+
+  if (FAILED(hr)) {
+    MOZ_LOG(sTaskbarConcealerLog, LogLevel::Error,
+            ("Call to PrepareFullScreenHWND(%p, %s) failed with nsresult %x",
+             aWnd, sMark, hr));
+  }
+};
+
+/**************************************************************
+ *
+ * SECTION: TaskbarConcealer event callbacks
+ *
+ **************************************************************/
+
+void nsWindow::TaskbarConcealer::OnWindowDestroyed(HWND aWnd) {
+  if (!UseAlternateFullscreenHeuristics()) {
+    return;
+  }
+
+  MOZ_LOG(sTaskbarConcealerLog, LogLevel::Info,
+          ("==> OnWindowDestroyed() for HWND %p", aWnd));
+
+  UpdateAllState(aWnd);
+}
+
+void nsWindow::TaskbarConcealer::OnFocusAcquired(nsWindow* aWin) {
+  if (!UseAlternateFullscreenHeuristics()) {
+    return;
+  }
+
+  // Update state unconditionally.
+  //
+  // This is partially because focus-acquisition only updates the z-order, which
+  // we don't cache and therefore can't notice changes to -- but also because
+  // it's probably a good idea to give the user a natural way to refresh the
+  // current fullscreen-marking state if it's somehow gone bad.
+
+  MOZ_LOG(sTaskbarConcealerLog, LogLevel::Info,
+          ("==> OnFocusAcquired() for HWND %p on HMONITOR %p", aWin->mWnd,
+           ::MonitorFromWindow(aWin->mWnd, MONITOR_DEFAULTTONULL)));
+
+  UpdateAllState();
+}
+
+void nsWindow::TaskbarConcealer::OnFullscreenChanged(nsWindow* aWin,
+                                                     bool enteredFullscreen) {
+  if (!UseAlternateFullscreenHeuristics()) {
+    TaskbarConcealerImpl().MarkAsHidingTaskbar(aWin->mWnd, enteredFullscreen);
+    return;
+  }
+
+  MOZ_LOG(sTaskbarConcealerLog, LogLevel::Info,
+          ("==> OnFullscreenChanged() for HWND %p on HMONITOR %p", aWin->mWnd,
+           ::MonitorFromWindow(aWin->mWnd, MONITOR_DEFAULTTONULL)));
+
+  UpdateAllState();
+}
+
+void nsWindow::TaskbarConcealer::OnWindowPosChanged(nsWindow* aWin) {
+  if (!UseAlternateFullscreenHeuristics()) {
+    return;
+  }
+
+  // Optimization: don't bother updating the state if the window hasn't moved
+  // (including appearances and disappearances).
+  const HWND myHwnd = aWin->mWnd;
+  const HMONITOR oldMonitor = sKnownWindows.Get(myHwnd);  // or nullptr
+  const HMONITOR newMonitor = GetWindowState(myHwnd)
+                                  .map([](auto state) { return state.monitor; })
+                                  .valueOr(nullptr);
+
+  if (oldMonitor == newMonitor) {
+    return;
+  }
+
+  MOZ_LOG(sTaskbarConcealerLog, LogLevel::Info,
+          ("==> OnWindowPosChanged() for HWND %p (HMONITOR %p -> %p)", myHwnd,
+           oldMonitor, newMonitor));
+
+  UpdateAllState();
+}
+
+void nsWindow::TaskbarConcealer::OnCloakChanged() {
+  if (!UseAlternateFullscreenHeuristics()) {
+    return;
+  }
+
+  MOZ_LOG(sTaskbarConcealerLog, LogLevel::Info, ("==> OnCloakChanged()"));
+
+  UpdateAllState();
+}