Implement toggle-windowed-fullscreen

Windowed, or fake, or detached, fullscreen, is when a window thinks that it's
fullscreen, but the compositor treats it as a normal window.

niri-config/src/lib.rs

@@ -1476,6 +1476,9 @@ pub enum Action {
     FullscreenWindow,
     #[knuffel(skip)]
     FullscreenWindowById(u64),
+    ToggleWindowedFullscreen,
+    #[knuffel(skip)]
+    ToggleWindowedFullscreenById(u64),
     #[knuffel(skip)]
     FocusWindow(u64),
     FocusWindowInColumn(#[knuffel(argument)] u8),
@@ -1680,6 +1683,12 @@ impl From<niri_ipc::Action> for Action {
             niri_ipc::Action::CloseWindow { id: Some(id) } => Self::CloseWindowById(id),
             niri_ipc::Action::FullscreenWindow { id: None } => Self::FullscreenWindow,
             niri_ipc::Action::FullscreenWindow { id: Some(id) } => Self::FullscreenWindowById(id),
+            niri_ipc::Action::ToggleWindowedFullscreen { id: None } => {
+                Self::ToggleWindowedFullscreen
+            }
+            niri_ipc::Action::ToggleWindowedFullscreen { id: Some(id) } => {
+                Self::ToggleWindowedFullscreenById(id)
+            }
             niri_ipc::Action::FocusWindow { id } => Self::FocusWindow(id),
             niri_ipc::Action::FocusWindowInColumn { index } => Self::FocusWindowInColumn(index),
             niri_ipc::Action::FocusWindowPrevious {} => Self::FocusWindowPrevious,

niri-ipc/src/lib.rs

@@ -221,6 +221,18 @@ pub enum Action {
         #[cfg_attr(feature = "clap", arg(long))]
         id: Option<u64>,
     },
+    /// Toggle windowed (fake) fullscreen on a window.
+    #[cfg_attr(
+        feature = "clap",
+        clap(about = "Toggle windowed (fake) fullscreen on the focused window")
+    )]
+    ToggleWindowedFullscreen {
+        /// Id of the window to toggle windowed fullscreen of.
+        ///
+        /// If `None`, uses the focused window.
+        #[cfg_attr(feature = "clap", arg(long))]
+        id: Option<u64>,
+    },
     /// Focus a window by id.
     FocusWindow {
         /// Id of the window to focus.

src/input/mod.rs

@@ -690,6 +690,23 @@ impl State {
                     self.niri.queue_redraw_all();
                 }
             }
+            Action::ToggleWindowedFullscreen => {
+                let focus = self.niri.layout.focus().map(|m| m.window.clone());
+                if let Some(window) = focus {
+                    self.niri.layout.toggle_windowed_fullscreen(&window);
+                    // FIXME: granular
+                    self.niri.queue_redraw_all();
+                }
+            }
+            Action::ToggleWindowedFullscreenById(id) => {
+                let window = self.niri.layout.windows().find(|(_, m)| m.id().get() == id);
+                let window = window.map(|(_, m)| m.window.clone());
+                if let Some(window) = window {
+                    self.niri.layout.toggle_windowed_fullscreen(&window);
+                    // FIXME: granular
+                    self.niri.queue_redraw_all();
+                }
+            }
             Action::FocusWindow(id) => {
                 let window = self.niri.layout.windows().find(|(_, m)| m.id().get() == id);
                 let window = window.map(|(_, m)| m.window.clone());

src/layout/mod.rs

@@ -244,6 +244,13 @@ pub trait LayoutElement {
         Some(requested)
     }
 
+    fn is_pending_windowed_fullscreen(&self) -> bool {
+        false
+    }
+    fn request_windowed_fullscreen(&mut self, value: bool) {
+        let _ = value;
+    }
+
     fn is_child_of(&self, parent: &Self) -> bool;
 
     fn rules(&self) -> &ResolvedWindowRules;
@@ -3458,6 +3465,20 @@ impl<W: LayoutElement> Layout<W> {
     }
 
     pub fn set_fullscreen(&mut self, id: &W::Id, is_fullscreen: bool) {
+        // Check if this is a request to unset the windowed fullscreen state.
+        if !is_fullscreen {
+            let mut handled = false;
+            self.with_windows_mut(|window, _| {
+                if window.id() == id && window.is_pending_windowed_fullscreen() {
+                    window.request_windowed_fullscreen(false);
+                    handled = true;
+                }
+            });
+            if handled {
+                return;
+            }
+        }
+
         if let Some(InteractiveMoveState::Moving(move_)) = &self.interactive_move {
             if move_.tile.window().id() == id {
                 return;
@@ -3487,6 +3508,26 @@ impl<W: LayoutElement> Layout<W> {
         }
     }
 
+    pub fn toggle_windowed_fullscreen(&mut self, id: &W::Id) {
+        let (_, window) = self.windows().find(|(_, win)| win.id() == id).unwrap();
+        if window.is_pending_fullscreen() {
+            // Remove the real fullscreen.
+            for ws in self.workspaces_mut() {
+                if ws.has_window(id) {
+                    ws.set_fullscreen(id, false);
+                    break;
+                }
+            }
+        }
+
+        // This will switch is_pending_fullscreen() to false right away.
+        self.with_windows_mut(|window, _| {
+            if window.id() == id {
+                window.request_windowed_fullscreen(!window.is_pending_windowed_fullscreen());
+            }
+        });
+    }
+
     pub fn workspace_switch_gesture_begin(&mut self, output: &Output, is_touchpad: bool) {
         let monitors = match &mut self.monitor_set {
             MonitorSet::Normal { monitors, .. } => monitors,

src/layout/tests.rs

@@ -29,6 +29,8 @@ struct TestWindowInner {
     pending_fullscreen: Cell<bool>,
     pending_activated: Cell<bool>,
     is_fullscreen: Cell<bool>,
+    is_windowed_fullscreen: Cell<bool>,
+    is_pending_windowed_fullscreen: Cell<bool>,
 }
 
 #[derive(Debug, Clone)]
@@ -72,6 +74,8 @@ impl TestWindow {
             pending_fullscreen: Cell::new(false),
             pending_activated: Cell::new(false),
             is_fullscreen: Cell::new(false),
+            is_windowed_fullscreen: Cell::new(false),
+            is_pending_windowed_fullscreen: Cell::new(false),
         }))
     }
 
@@ -101,6 +105,13 @@ impl TestWindow {
             changed = true;
         }
 
+        if self.0.is_windowed_fullscreen.get() != self.0.is_pending_windowed_fullscreen.get() {
+            self.0
+                .is_windowed_fullscreen
+                .set(self.0.is_pending_windowed_fullscreen.get());
+            changed = true;
+        }
+
         changed
     }
 }
@@ -144,6 +155,10 @@ impl LayoutElement for TestWindow {
     ) {
         self.0.requested_size.set(Some(size));
         self.0.pending_fullscreen.set(is_fullscreen);
+
+        if is_fullscreen {
+            self.0.is_pending_windowed_fullscreen.set(false);
+        }
     }
 
     fn min_size(&self) -> Size<i32, Logical> {
@@ -191,10 +206,18 @@ impl LayoutElement for TestWindow {
     fn set_floating(&mut self, _floating: bool) {}
 
     fn is_fullscreen(&self) -> bool {
+        if self.0.is_windowed_fullscreen.get() {
+            return false;
+        }
+
         self.0.is_fullscreen.get()
     }
 
     fn is_pending_fullscreen(&self) -> bool {
+        if self.0.is_pending_windowed_fullscreen.get() {
+            return false;
+        }
+
         self.0.pending_fullscreen.get()
     }
 
@@ -202,6 +225,14 @@ impl LayoutElement for TestWindow {
         self.0.requested_size.get()
     }
 
+    fn is_pending_windowed_fullscreen(&self) -> bool {
+        self.0.is_pending_windowed_fullscreen.get()
+    }
+
+    fn request_windowed_fullscreen(&mut self, value: bool) {
+        self.0.is_pending_windowed_fullscreen.set(value);
+    }
+
     fn is_child_of(&self, parent: &Self) -> bool {
         self.0.parent_id.get() == Some(parent.0.id)
     }
@@ -374,6 +405,7 @@ enum Op {
         window: usize,
         is_fullscreen: bool,
     },
+    ToggleWindowedFullscreen(#[proptest(strategy = "1..=5usize")] usize),
     FocusColumnLeft,
     FocusColumnRight,
     FocusColumnFirst,
@@ -901,14 +933,26 @@ impl Op {
                 layout.remove_window(&id, Transaction::new());
             }
             Op::FullscreenWindow(id) => {
+                if !layout.has_window(&id) {
+                    return;
+                }
                 layout.toggle_fullscreen(&id);
             }
             Op::SetFullscreenWindow {
                 window,
                 is_fullscreen,
             } => {
+                if !layout.has_window(&window) {
+                    return;
+                }
                 layout.set_fullscreen(&window, is_fullscreen);
             }
+            Op::ToggleWindowedFullscreen(id) => {
+                if !layout.has_window(&id) {
+                    return;
+                }
+                layout.toggle_windowed_fullscreen(&id);
+            }
             Op::FocusColumnLeft => layout.focus_left(),
             Op::FocusColumnRight => layout.focus_right(),
             Op::FocusColumnFirst => layout.focus_column_first(),
@@ -3187,6 +3231,37 @@ fn unfullscreen_with_large_border() {
     check_ops_with_options(options, &ops);
 }
 
+#[test]
+fn fullscreen_to_windowed_fullscreen() {
+    let ops = [
+        Op::AddOutput(0),
+        Op::AddWindow {
+            params: TestWindowParams::new(0),
+        },
+        Op::FullscreenWindow(0),
+        Op::Communicate(0), // Make sure it goes into fullscreen.
+        Op::ToggleWindowedFullscreen(0),
+    ];
+
+    check_ops(&ops);
+}
+
+#[test]
+fn windowed_fullscreen_to_fullscreen() {
+    let ops = [
+        Op::AddOutput(0),
+        Op::AddWindow {
+            params: TestWindowParams::new(0),
+        },
+        Op::FullscreenWindow(0),
+        Op::Communicate(0),              // Commit fullscreen state.
+        Op::ToggleWindowedFullscreen(0), // Switch is_fullscreen() to false.
+        Op::FullscreenWindow(0),         // Switch is_fullscreen() back to true.
+    ];
+
+    check_ops(&ops);
+}
+
 fn parent_id_causes_loop(layout: &Layout<TestWindow>, id: usize, mut parent_id: usize) -> bool {
     if parent_id == id {
         return true;

src/window/mapped.rs

@@ -120,6 +120,36 @@ pub struct Mapped {
     ///
     /// Used for double-resize-click tracking.
     last_interactive_resize_start: Cell<Option<(Duration, ResizeEdge)>>,
+
+    /// Whether this window is in windowed (fake) fullscreen.
+    ///
+    /// In this mode, the underlying window is told that it's fullscreen, while keeping it as
+    /// a regular, non-fullscreen tile.
+    is_windowed_fullscreen: bool,
+
+    /// Whether this window is pending to go to windowed (fake) fullscreen.
+    ///
+    /// Several places in the layout code assume that is_fullscreen() can flip only on a commit.
+    /// Which is something that we do want to flip when changing is_windowed_fullscreen. Flipping
+    /// it right away would mean remembering to call layout.update_window() after any operation
+    /// that may change is_windowed_fullscreen, which is quite tricky and error-prone, especially
+    /// for deeply nested operations.
+    ///
+    /// It's also not clear what's the best way to go about it. Ideally we'd wait for configure ack
+    /// and commit before "committing" to is_windowed_fullscreen, however, since it's not real
+    /// Wayland state, we may end up with no Wayland state change to configure at all.
+    ///
+    /// For example: when the window is in real fullscreen, but its non-fullscreen size matches
+    /// its fullscreen size. Then turning on is_windowed_fullscreen will both keep the
+    /// fullscreen state, and keep the size (since it matches), resulting in no configure.
+    ///
+    /// So we work around this by "committing" is_pending_windowed_fullscreen to
+    /// is_windowed_fullscreen on receiving any actual window commit, and whenever
+    /// is_pending_windowed_fullscreen changes, we mark the window as needs_configure. This does
+    /// mean some unnecessary delays in some cases, but it also means being able to better
+    /// synchronize our windowed fullscreen state to the real window updates, so that's good I
+    /// guess.
+    is_pending_windowed_fullscreen: bool,
 }
 
 niri_render_elements! {
@@ -209,6 +239,8 @@ impl Mapped {
             pending_transactions: Vec::new(),
             interactive_resize: None,
             last_interactive_resize_start: Cell::new(None),
+            is_windowed_fullscreen: false,
+            is_pending_windowed_fullscreen: false,
         }
     }
 
@@ -608,10 +640,21 @@ impl LayoutElement for Mapped {
         animate: bool,
         transaction: Option<Transaction>,
     ) {
+        // Going into real fullscreen resets windowed fullscreen.
+        if is_fullscreen {
+            self.is_pending_windowed_fullscreen = false;
+
+            if self.is_windowed_fullscreen {
+                // Make sure we receive a commit to update self.is_windowed_fullscreen to false
+                // later on.
+                self.needs_configure = true;
+            }
+        }
+
         let changed = self.toplevel().with_pending_state(|state| {
             let changed = state.size != Some(size);
             state.size = Some(size);
-            if is_fullscreen {
+            if is_fullscreen || self.is_pending_windowed_fullscreen {
                 state.states.set(xdg_toplevel::State::Fullscreen);
             } else {
                 state.states.unset(xdg_toplevel::State::Fullscreen);
@@ -660,7 +703,8 @@ impl LayoutElement for Mapped {
 
             let same_size = last_sent.size.unwrap_or_default() == size;
             let has_fullscreen = last_sent.states.contains(xdg_toplevel::State::Fullscreen);
-            (same_size && !has_fullscreen).then_some(last_serial)
+            let same_fullscreen = has_fullscreen == self.is_pending_windowed_fullscreen;
+            (same_size && same_fullscreen).then_some(last_serial)
         });
 
         if let Some(serial) = already_sent {
@@ -687,7 +731,9 @@ impl LayoutElement for Mapped {
         let changed = self.toplevel().with_pending_state(|state| {
             let changed = state.size != Some(size);
             state.size = Some(size);
-            state.states.unset(xdg_toplevel::State::Fullscreen);
+            if !self.is_pending_windowed_fullscreen {
+                state.states.unset(xdg_toplevel::State::Fullscreen);
+            }
             changed
         });
 
@@ -934,6 +980,10 @@ impl LayoutElement for Mapped {
     }
 
     fn is_fullscreen(&self) -> bool {
+        if self.is_windowed_fullscreen {
+            return false;
+        }
+
         with_toplevel_role(self.toplevel(), |role| {
             role.current
                 .states
@@ -942,6 +992,10 @@ impl LayoutElement for Mapped {
     }
 
     fn is_pending_fullscreen(&self) -> bool {
+        if self.is_pending_windowed_fullscreen {
+            return false;
+        }
+
         self.toplevel()
             .with_pending_state(|state| state.states.contains(xdg_toplevel::State::Fullscreen))
     }
@@ -1014,7 +1068,7 @@ impl LayoutElement for Mapped {
 
         if let Some((mut size, fullscreen)) = pending {
             // If the pending change is fullscreen, we can't use that size.
-            if fullscreen {
+            if fullscreen && !self.is_pending_windowed_fullscreen {
                 return None;
             }
 
@@ -1034,6 +1088,33 @@ impl LayoutElement for Mapped {
         }
     }
 
+    fn is_pending_windowed_fullscreen(&self) -> bool {
+        self.is_pending_windowed_fullscreen
+    }
+
+    fn request_windowed_fullscreen(&mut self, value: bool) {
+        if self.is_pending_windowed_fullscreen == value {
+            return;
+        }
+
+        self.is_pending_windowed_fullscreen = value;
+
+        // Set the fullscreen state to match.
+        //
+        // When going from windowed to real fullscreen, we'll use request_size() which will set the
+        // fullscreen state back.
+        self.toplevel().with_pending_state(|state| {
+            if value {
+                state.states.set(xdg_toplevel::State::Fullscreen);
+            } else {
+                state.states.unset(xdg_toplevel::State::Fullscreen);
+            }
+        });
+
+        // Make sure we recieve a commit later to update self.is_windowed_fullscreen.
+        self.needs_configure = true;
+    }
+
     fn is_child_of(&self, parent: &Self) -> bool {
         self.toplevel().parent().as_ref() == Some(parent.toplevel().wl_surface())
     }
@@ -1098,5 +1179,12 @@ impl LayoutElement for Mapped {
                 self.request_size_once = Some(RequestSizeOnce::UseWindowSize);
             }
         }
+
+        // HACK: this is not really accurate because the commit might be for an earlier serial than
+        // when we requested windowed fullscren. But we don't actually care much, since this is
+        // entirely compositor state. We're only tying it to configure/commit as a workaround to
+        // the rest of the code expecting that fullscreen doesn't suddenly just change in the
+        // middle of something.
+        self.is_windowed_fullscreen = self.is_pending_windowed_fullscreen;
     }
 }