shell: handle fullscreen windows on a dedicated layer

I hoped to split this up into multiple commits, but the api
changes to `shell/workspace.rs` were to invasive to feasibly do this.

Here is a rough list of changes:

- Fullscreen windows aren't mapped to other layers anymore
  - This they need their own logic for:
    - Sending frames
    - Dmabuf Feedback
    - Primary outputs
    - On commit handlers
    - cursor tests
  - They get their own unmap/remap logic
  - They get a new restore state similar to minimized windows
    - Refactored the minimized window state to reuse as much as possible
      here
  - They need to be part of focus stacks, which means adjusting them
    to a new type `FocusTarget` as they previously only handled
    `CosmicMapped`.
  - Various shell handlers (minimize, move, menu) now have dedicated
    logic for fullscreen surfaces
    - This was partially necessary due to relying on CosmicSurface now,
      partially because they should've had their own logic from the
      start. E.g. the context menu is now reflecting the fullscreen
      state
- Fullscreen windows may be rendered behind other windows now, when they
  loose focus.
  - This needed changes to input handling / rendering

src/wayland/handlers/toplevel_management.rs

@@ -6,10 +6,11 @@ use smithay::{
     output::Output,
     reexports::wayland_server::DisplayHandle,
     utils::{Point, Rectangle, Size, SERIAL_COUNTER},
+    wayland::seat::WaylandFocus,
 };
 
 use crate::{
-    shell::{element::CosmicWindow, CosmicSurface, Shell, WorkspaceDelta},
+    shell::{focus::target::KeyboardFocusTarget, CosmicSurface, Shell, WorkspaceDelta},
     utils::prelude::*,
     wayland::protocols::{
         toplevel_info::ToplevelInfoHandler,
@@ -41,17 +42,13 @@ impl ToplevelManagementHandler for State {
                 .spaces_for_output(output)
                 .enumerate()
                 .find(|(_, w)| {
-                    w.mapped()
-                        .flat_map(|m| m.windows().map(|(s, _)| s))
-                        .any(|w| &w == window)
+                    w.get_fullscreen().is_some_and(|f| f == window)
+                        || w.mapped()
+                            .flat_map(|m| m.windows().map(|(s, _)| s))
+                            .any(|w| &w == window)
                 });
             if let Some((idx, workspace)) = maybe {
                 let seat = seat.unwrap_or(shell.seats.last_active().clone());
-                let mapped = workspace
-                    .mapped()
-                    .find(|m| m.windows().any(|(w, _)| &w == window))
-                    .unwrap()
-                    .clone();
 
                 let handle = workspace.handle;
                 let res = shell.activate(
@@ -62,8 +59,12 @@ impl ToplevelManagementHandler for State {
                 );
 
                 let workspace = shell.workspaces.space_for_handle_mut(&handle).unwrap();
-                if seat.get_keyboard().unwrap().current_focus() != Some(mapped.clone().into())
-                    && workspace.is_tiled(&mapped)
+                if seat
+                    .get_keyboard()
+                    .unwrap()
+                    .current_focus()
+                    .is_some_and(|focus| !focus.windows().any(|w| w == *window))
+                    && workspace.is_tiled(window)
                 {
                     for mapped in workspace
                         .mapped()
@@ -75,6 +76,13 @@ impl ToplevelManagementHandler for State {
                         workspace.unmaximize_request(&mapped);
                     }
                 }
+
+                let target = if let Some(mapped) = workspace.element_for_surface(window) {
+                    mapped.focus_window(window);
+                    KeyboardFocusTarget::Element(mapped.clone())
+                } else {
+                    KeyboardFocusTarget::Fullscreen(window.clone())
+                };
                 std::mem::drop(shell);
 
                 if seat.active_output() != *output {
@@ -102,8 +110,7 @@ impl ToplevelManagementHandler for State {
                     }
                 }
 
-                mapped.focus_window(window);
-                Shell::set_focus(self, Some(&mapped.clone().into()), &seat, None, false);
+                Shell::set_focus(self, Some(&target), &seat, None, false);
                 return;
             }
         }
@@ -121,44 +128,27 @@ impl ToplevelManagementHandler for State {
         _output: Output,
     ) {
         let mut shell = self.common.shell.write();
-        if let Some(mut mapped) = shell.element_for_surface(window).cloned() {
-            if let Some(from_workspace) = shell.space_for_mut(&mapped) {
-                // If window is part of a stack, remove it and map it outside the stack
-                if let Some(stack) = mapped.stack_ref() {
-                    stack.remove_window(&window);
-                    mapped = CosmicWindow::new(
-                        window.clone(),
-                        self.common.event_loop_handle.clone(),
-                        self.common.theme.clone(),
-                    )
-                    .into();
-                    if from_workspace.tiling_enabled {
-                        from_workspace.tiling_layer.map(
-                            mapped.clone(),
-                            None::<std::iter::Empty<_>>,
-                            None,
-                        );
-                    } else {
-                        from_workspace.floating_layer.map(mapped.clone(), None);
-                    }
-                }
+        let seat = shell.seats.last_active().clone();
+        let Some(surface) = window.wl_surface() else {
+            return;
+        };
+        let Some((from_workspace, _)) = shell.workspace_for_surface(&*surface) else {
+            return;
+        };
 
-                let from_handle = from_workspace.handle;
-                let seat = shell.seats.last_active().clone();
-                let res = shell.move_window(
-                    Some(&seat),
-                    &mapped,
-                    &from_handle,
-                    &to_handle,
-                    false,
-                    None,
-                    &mut self.common.workspace_state.update(),
-                );
-                if let Some((target, _)) = res {
-                    std::mem::drop(shell);
-                    Shell::set_focus(self, Some(&target), &seat, None, true);
-                }
-            }
+        let res = shell.move_window(
+            Some(&seat),
+            window,
+            &from_workspace,
+            &to_handle,
+            false,
+            None,
+            &mut self.common.workspace_state.update(),
+            &self.common.event_loop_handle,
+        );
+        if let Some((target, _)) = res {
+            std::mem::drop(shell);
+            Shell::set_focus(self, Some(&target), &seat, None, true);
         }
     }
 
@@ -170,23 +160,18 @@ impl ToplevelManagementHandler for State {
     ) {
         let mut shell = self.common.shell.write();
         let seat = shell.seats.last_active().clone();
-        if let Some(mapped) = shell.element_for_surface(window).cloned() {
-            if let Some((output, workspace)) =
-                output.and_then(|output| shell.workspaces.active_mut(&output).map(|w| (output, w)))
-            {
-                let from = minimize_rectangle(&output, window);
-                workspace.fullscreen_request(window, None, from, &seat);
-            } else if let Some((output, handle)) = shell
-                .space_for(&mapped)
-                .map(|workspace| (workspace.output.clone(), workspace.handle.clone()))
-            {
-                let from = minimize_rectangle(&output, window);
-                shell
-                    .workspaces
-                    .space_for_handle_mut(&handle)
-                    .unwrap()
-                    .fullscreen_request(window, None, from, &seat);
-            }
+        let output = output
+            .or_else(|| {
+                window
+                    .wl_surface()
+                    .and_then(|surface| shell.visible_output_for_surface(&*surface).cloned())
+            })
+            .unwrap_or_else(|| seat.focused_or_active_output());
+        if let Some(target) =
+            shell.fullscreen_request(window, output, &self.common.event_loop_handle)
+        {
+            std::mem::drop(shell);
+            Shell::set_focus(self, Some(&target), &seat, None, true);
         }
     }
 
@@ -196,33 +181,14 @@ impl ToplevelManagementHandler for State {
         window: &<Self as ToplevelInfoHandler>::Window,
     ) {
         let mut shell = self.common.shell.write();
-        if let Some(mapped) = shell.element_for_surface(window).cloned() {
-            if let Some(workspace) = shell.space_for_mut(&mapped) {
-                if let Some((layer, previous_workspace)) = workspace.unfullscreen_request(window) {
-                    let old_handle = workspace.handle.clone();
-                    let new_workspace_handle = shell
-                        .workspaces
-                        .space_for_handle(&previous_workspace)
-                        .is_some()
-                        .then_some(previous_workspace)
-                        .unwrap_or(old_handle); // if the workspace doesn't exist anymore, we can still remap on the right layer
-
-                    shell.remap_unfullscreened_window(
-                        mapped,
-                        &old_handle,
-                        &new_workspace_handle,
-                        layer,
-                    );
-                }
-            }
-        }
+        shell.unfullscreen_request(window, &self.common.event_loop_handle);
     }
 
     fn maximize(&mut self, _dh: &DisplayHandle, window: &<Self as ToplevelInfoHandler>::Window) {
         let mut shell = self.common.shell.write();
         if let Some(mapped) = shell.element_for_surface(window).cloned() {
             let seat = shell.seats.last_active().clone();
-            shell.maximize_request(&mapped, &seat, true);
+            shell.maximize_request(&mapped, &seat, true, &self.common.event_loop_handle);
         }
     }
 
@@ -235,22 +201,13 @@ impl ToplevelManagementHandler for State {
 
     fn minimize(&mut self, _dh: &DisplayHandle, window: &<Self as ToplevelInfoHandler>::Window) {
         let mut shell = self.common.shell.write();
-        if let Some(mapped) = shell.element_for_surface(window).cloned() {
-            if !mapped.is_stack() || &mapped.active_window() == window {
-                shell.minimize_request(&mapped);
-            }
-        }
+        shell.minimize_request(window);
     }
 
     fn unminimize(&mut self, _dh: &DisplayHandle, window: &<Self as ToplevelInfoHandler>::Window) {
         let mut shell = self.common.shell.write();
-        if let Some(mapped) = shell.element_for_surface(window).cloned() {
-            let seat = shell.seats.last_active().clone();
-            shell.unminimize_request(&mapped, &seat);
-            if mapped.is_stack() {
-                mapped.stack_ref().unwrap().set_active(window);
-            }
-        }
+        let seat = shell.seats.last_active().clone();
+        shell.unminimize_request(window, &seat, &self.common.event_loop_handle);
     }
 
     fn set_sticky(&mut self, _dh: &DisplayHandle, window: &<Self as ToplevelInfoHandler>::Window) {