Show/Hide attached surfaces when entering/exiting from fullscreen #4664

tarek-y-ismail · 2026-02-04T11:29:22Z

What's new?

Adds code BasicWindowManager to hide/restore attached surfaces in the "above" layer when a surface is fullscreened, unfullscreened, and removed.

How to test

Scenario 1: waybar on the above layer + fullscreen app

Run mir with layer shell:

miral-app --add-wayland-extensions=zwlr_layer_shell_v1

Set waybar to be on the "bottom" layer (~/.config/waybar/config):

{
    "layer": "bottom", // Waybar at top layer
   ...
}

Start an application, a terminal for example
Maximize it, it should take up all screen area until it hits waybar.
Fullscreen it, it should take up the whole output
Change the layer configuration waybar's config to be "top"
Repeat step 4. Behavior should be identical
Repeat step 5. Behavior should be identical

Scenario 2: Multiple outputs

Start mir with multiple virtual outputs:

   miral-app --add-wayland-extensions=zwlr_layer_shell_v1  --x11-output=960x500:400x400

Start a terminal via CTRL + ALT + t
Make sure waybar is configured on the top layer and start it
Fullscreen the terminal via F11
Waybar should be hidden on the output where the terminal is fullscreened, and still visible on the other output
Un-fullscreen and move the terminal to the other output, then re-fullscreen
Behavior should be similar to step 5.

Scenario 3: Fullscreen app and OSK

Run mir with all extensions:

miral-app --add-wayland-extensions=all

Start a terminal via CTRL + ALT + t, run ubuntu-frame-osk
Start kate, open any text file. OSK should pop up.
Press F11 to fullscreen
OSK should be hidden.

Preferably, we'd like the OSK to be visible when an app is fullscreened, but since it's placed in the "above" layer, and we have no way in the layer shell protocol to identify it, it will be broken for now.

Scenario 4: Waybar + Fullscreen app + non-fullscreen app
This follows scenario 1, with the following extra steps

Run a different fullscreen app, a terminal via CTRL + ALT + t for example
Focus should switch to it, way bar should be visible once more
If you use the alt-tab switcher, waybar should hide and be restored as you focus on the fullscreened and non-fullscreened apps respectively.
Changing focus via the pointer should behave similarly to step 3

Scenario 5: Waybar + Fullscreen app exits
Repeat scenario 1. Then close the app via a shortcut. If using a terminal, CTRL + D. Waybar should pop into view once more.

Scenario 5: Waybar + Fullscreen app with child surfaces

Repeat scenario 1, but with VLC.
With VLC fullscreened, open any entry from the menu bar
Waybar should remain hidden
Open a dialog via Media > Open File or Ctrl + o,
Way bar should remain hidden.

Scenario 6:
Same as scenario 4, but instead of switching focus between the two apps, you exit the non-fullscreen app first.

Focus should switch to the fullscreen app, and waybar should remain hidden.

Checklist

Tests added and pass (coming (if possible) once this approach is approved)
Adequate documentation added (coming (if possible) once this approach is approved)

src/miral/basic_window_manager.cpp

AlanGriffiths

No tests?

src/miral/basic_window_manager.cpp

src/miral/basic_window_manager.h

src/miral/basic_window_manager.cpp

AlanGriffiths · 2026-02-04T15:49:11Z

src/miral/basic_window_manager.cpp

+    bool const was_fullscreen{info.state() == mir_window_state_fullscreen};
+    if (was_fullscreen)


No need for a variable (especially with scope beyond the if statement).

But... does this code belong here anyway? I mean, if the focus shifts to another fullscreen window we need to undo this work.

Instead, when a window (or no window) gets focus we should be checking the state of the attached windows and acting accordingly.

I looked into it. This is the latest we can do this check. It was added specifically for the case where you have a fullscreen window, and you close it without exiting fullscreen first.

In that case, a few lines later, the info for this window will be erased before we reach the focus checking code, so we won't be able to move this code there.

src/miral/basic_window_manager.cpp

mattkae

An initial ask!

src/miral/basic_window_manager.cpp

states They are attached! The previous state is constant for all of them!

Mir saw that the buffer is not mapped, but the client submitted a buffer with a size, so it sets its status to restored. `place_and_size_for_state` then sees that the attached client is not overlapping with the application zone. Which is correct because application zones shrink for attached surfaces with exclusion zones. It then tries to center the surface in the application zone, causing clients like waybar, ironbar, and gbar to appear in the middle of the screen when they try submitting a buffer while hidden under a fullscreen app.

…p to a fullscreen app

surfaces

tarek-y-ismail · 2026-02-06T18:31:05Z

Something I've just realized is that I haven't taken into account cases where focus changes (or a surface is closed) with the closed surface and the newly focused surface on different outputs/display areas. So far I've assumed both are on the same display area.

Another thing I should mention is that focus handling feels quite messy at the moment. For example, when we have two apps open. Let's call them A and B. If we close A, remove_window gets called which removes the window and updates the MRU window stack among other things. active_window() now returns B .

Context:

mir/src/miral/basic_window_manager.cpp

Lines 327 to 349 in 38d8e69

    
           policy->advise_delete_window(info); 
        
           info_for(application).remove_window(info.window()); 
        
           mru_active_windows.erase(info.window()); 
        
           fullscreen_surfaces.erase(info.window()); 
        
           for (auto& area : display_areas) 
        
           { 
        
               area->attached_windows.erase(info.window()); 
        
               std::erase(area->hidden_attached_windows, info.window()); 
        
           } 
        
           if (info.state() == mir_window_state_attached && 
        
               info.exclusive_rect().is_set()) 
        
           { 
        
               update_application_zones_and_attached_windows(); 
        
           } 
        
           application->destroy_surface(info.window()); 
        
           bool const prev_was_fullscreen{info.state() == mir_window_state_fullscreen}; 
        
           // NB erase() invalidates info, but we want to keep access to "parent". 
        
           auto const parent = info.parent(); 
        
           auto const prev_display_area = display_area_for(info); 
        
           erase(info);

mir/src/miral/basic_window_manager.cpp

Lines 578 to 581 in 38d8e69

    
           auto miral::BasicWindowManager::active_window() const -> Window 
        
           { 
        
               return allow_active_window ? mru_active_windows.top() : Window{}; 
        
           }

We also call refocus, for which itself traverses the MRU window stack from top to bottom, starting with B.

mir/src/miral/basic_window_manager.cpp

Lines 385 to 402 in 38d8e69

    
           mru_active_windows.enumerate([&](miral::Window& window) 
        
               { 
        
                   // select_active_window() calls set_focus_to() which updates mru_active_windows and changes window 
        
                   auto const w = window; 
        
                   for (auto const& workspace : workspaces_containing(w)) 
        
                   { 
        
                       for (auto const& ww : workspaces_containing_window) 
        
                       { 
        
                           if (ww == workspace) 
        
                           { 
        
                               return !(new_focus = select_active_window(w)); 
        
                           } 
        
                       } 
        
                   } 
        
                   return true; 
        
               });

Then that calls set_active_window, and gets the active window, which is B.

mir/src/miral/basic_window_manager.cpp

Line 1703 in 38d8e69

auto const prev_window = active_window();

Then we execute the rest of set_active_window, which at that point we don't have information about the window we just removed!

Edit: I just realized that I've worked on this alone for 120% of my time today. So there might be a solution to the mini-rant above that my neurons are just too fried to see right now.

Should appease GCC

When there would be a layer shell surface with and a fullscreen surface on one output, and we click on empty space in the other output, this would cause the hidden layer shell surface to erroneously be restored.

its own private method

…al to its own private method

fullscreen

tarek-y-ismail · 2026-02-10T15:33:33Z

Bug: With two outputs, if we:

start a terminal (A),
start waybar, full screen the terminal,
and open a new terminal (B), waybar is restored as expected.
When terminal B is dragged to the second output, I believe the first output should hide waybar again. Will see if I can fix this, but leaving this here in case I can't immediately do so.

Edit: After thinking about it properly, no. waybar should not be automatically hidden. It will be hidden again if we focus terminal A, but it doesn't need to be hidden when focus is not on it.

src/miral/basic_window_manager.cpp

focused surface

surfaces

and window removal handling code

outputs

multiple outputs In that case, `current` was the attached surface on the other output, we later would return when seeing that it was not in the application layer, without restoring attached surfaces on the previous display area.

attached surfaces

AlanGriffiths

This seems messy.

I don't have a clear solution to offer, but trying to model a window state of "attached and hidden" as "hidden and in a list" introduces a lot of corner cases that might be avoided with another approach. (A separate "hidden" property or a new "attached and hidden" state.)

AlanGriffiths · 2026-02-11T10:12:20Z

src/miral/basic_window_manager.cpp

+        hidden_attached_windows.push_back(window);
+        bwm.set_state(info, mir_window_state_hidden);
+    }
+}


This mixing of logic across BasicWindowManager and DisplayArea seems inelegant.

Another way to divide the logic:

void miral::BasicWindowManager::DisplayArea::update_hidden_attached(std::function<bool(Window const& w) predicate) { // Copy as `predicate` may modify `attached_windows` and invalidate the iterator. auto const attached_windows = this->attached_windows; decltype(hidden_attached_windows) hidden_attached_windows; for (auto& window : attached_windows) { if (predicate(window)) { hidden_attached_windows.push_back(window); } } this->hidden_attached_windows = std:move(hidden_attached_windows); }

current_display_area->update_hidden_attached([this](Window const& w) { auto& info = info_for(window); if (info.depth_layer() != mir_depth_layer_above) return false; set_state(info, mir_window_state_hidden); return true; });

AlanGriffiths · 2026-02-11T10:13:04Z

src/miral/basic_window_manager.cpp

+}
+}
+
+void miral::BasicWindowManager::DisplayArea::hide_all_attached(BasicWindowManager& bwm)


The name is wrong - only some attached are hidden.

AlanGriffiths · 2026-02-11T10:16:44Z

src/miral/basic_window_manager.cpp

+    auto current = window;
+    while (current)
+    {
+        auto& info = bwm.info_for(current);
+        if (info.state() == mir_window_state_fullscreen)
+            return true;
+        current = info.parent();
+    }


Isn't this a weirdly written for loop?

AlanGriffiths · 2026-02-11T10:17:33Z

src/miral/basic_window_manager.cpp

+    if (!window)
+        return false;


Redundant check?

AlanGriffiths · 2026-02-11T10:18:29Z

src/miral/basic_window_manager.cpp

    rect.top_left.y = zone.top_left.y + 0.5 * std::max(DeltaY{}, zone.size.height - rect.size.height);
 }
+
+auto is_window_or_parent_fullscreen(miral::Window const& window, miral::BasicWindowManager& bwm) -> bool


Simpler as a BasicWindowManager member function?

AlanGriffiths · 2026-02-11T10:21:56Z

src/miral/basic_window_manager.cpp

+void miral::BasicWindowManager::DisplayArea::restore_all_attached(BasicWindowManager& bwm)
+{
+    for (auto& window : hidden_attached_windows)
+    {
+        if(!window)
+            continue;
+
+        auto& info = bwm.info_for(window);
+        bwm.set_state(info, mir_window_state_attached);
+    }
+
+    hidden_attached_windows.clear();
+}


Name wrong:

it is not all attached that are restored; and,

"restored" is a window state distinct from "attached"

AlanGriffiths · 2026-02-11T10:31:04Z

src/miral/basic_window_manager.cpp

+    // If a layer shell surface (waybar) tries to submit a buffer while
+    // its hidden (in favor of another fullscreen surface), don't try
+    // to modify its placement.
+    if (display_area_for(info)->is_hidden_attached(info))
+        mods.state().consume();


This seems overbroad: it bans any transitions. E.g. a panel that decides to transition from "attached" to "restored" (and, maybe, change layer too).

tarek-y-ismail commented Feb 4, 2026

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src/miral/basic_window_manager.cpp Outdated Show resolved Hide resolved

Show/Hide attached surfaces when entering/exiting from fullscreen

4a67dd1

tarek-y-ismail force-pushed the MIRENG-457/hide-attached-above-surfaces-when-fullscreened branch from e76e32d to 4a67dd1 Compare February 4, 2026 11:37

tarek-y-ismail requested review from AlanGriffiths and mattkae February 4, 2026 11:37

tarek-y-ismail marked this pull request as ready for review February 4, 2026 11:37

tarek-y-ismail requested a review from a team as a code owner February 4, 2026 11:37

AlanGriffiths requested changes Feb 4, 2026

View reviewed changes

mattkae requested changes Feb 5, 2026

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src/miral/basic_window_manager.cpp Show resolved Hide resolved

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tarek-y-ismail added 2 commits February 6, 2026 09:27

Remove accidental whitespace change

8cfa385

Skip restoring window if it becomes invalid

92d2eef

tarek-y-ismail mentioned this pull request Feb 6, 2026

Basic window manager cleanups #4669

Open

tarek-y-ismail added 9 commits February 6, 2026 17:41

Use set_state, and only store attached windows and not their previous

aaceb4a

states They are attached! The previous state is constant for all of them!

Take hidden attached windows into account for display_area_for

93fbe75

Add a fallback for restoring attached windows in select_active_window

345a39a

Move logic for handling hiding/restoring attached surface to set_state

5530ce8

Hide attached windows when focus goes from a closed non-fullscreen ap…

55fede6

…p to a fullscreen app

Add pre and post conditions to {hide,restore}_all_attached

a493ab2

Handle more cases of windows closing with hidden or visible attached

734012e

surfaces

Remove removed windows from hidden_attached_windows

38d8e69

tarek-y-ismail added 4 commits February 10, 2026 10:54

Add [[fallthrough]] for the fullscreen case in set_state

239641c

Should appease GCC

Don't restore layer shell surfaces when select_active_window fails

31297ff

When there would be a layer shell surface with and a fullscreen surface on one output, and we click on empty space in the other output, this would cause the hidden layer shell surface to erroneously be restored.

Move code to handle attached surface hiding/restoring on focus change to

9c5da9f

its own private method

Move code to handle attached surface hiding/restoring on window remov…

e66137e

…al to its own private method

tarek-y-ismail self-assigned this Feb 10, 2026

Add tests for hiding layer shell windows when applications are

2afe488

fullscreen

tarek-y-ismail requested review from AlanGriffiths and mattkae February 10, 2026 15:32

tarek-y-ismail commented Feb 11, 2026

View reviewed changes

src/miral/basic_window_manager.cpp Outdated Show resolved Hide resolved

tarek-y-ismail added 10 commits February 11, 2026 10:25

Format handle_attached_surfaces_for_window_removal

c7c0c53

Simplify handle_attached_surfaces_for_window_removal to only check the

ba8b0f5

focused surface

Focusing on a window in another display are should not restore attached

66d4757

surfaces

Simplify attached surface hiding/restoring logic by merging focus change

15a8cc5

and window removal handling code

Add more tests for hiding/restoring attached surfaces with multiple

5815eca

outputs

Cache info_for results

a96f9a9

Remove extra newline

bb98a6f

Add test case for closing a fullscreen window with multiple outputs and

681cbe1

attached surfaces

Add a name to the parameter of {hide,restore}_all_attached

bf26f01

AlanGriffiths requested changes Feb 11, 2026

View reviewed changes

		bool const was_fullscreen{info.state() == mir_window_state_fullscreen};
		if (was_fullscreen)

Show/Hide attached surfaces when entering/exiting from fullscreen #4664

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Show/Hide attached surfaces when entering/exiting from fullscreen #4664

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