Add x11 window type settings to viewport builder (#4175)

Not sure about the api, currently I've mapped the whole XWindowType
enum, but maybe there's something more sensible to do?

* Closes <https://github.com/emilk/egui/issues/4150>

---------

Co-authored-by: Emil Ernerfeldt <emil.ernerfeldt@gmail.com>

crates/egui-winit/src/lib.rs

@@ -1540,6 +1540,9 @@ pub fn create_winit_window_builder<T>(
         // wayland:
         app_id: _app_id,
 
+        // x11
+        window_type: _window_type,
+
         mouse_passthrough: _, // handled in `apply_viewport_builder_to_window`
     } = viewport_builder;
 
@@ -1612,6 +1615,30 @@ pub fn create_winit_window_builder<T>(
         window_builder = window_builder.with_name(app_id, "");
     }
 
+    #[cfg(all(feature = "x11", target_os = "linux"))]
+    {
+        if let Some(window_type) = _window_type {
+            use winit::platform::x11::WindowBuilderExtX11 as _;
+            use winit::platform::x11::XWindowType;
+            window_builder = window_builder.with_x11_window_type(vec![match window_type {
+                egui::X11WindowType::Normal => XWindowType::Normal,
+                egui::X11WindowType::Utility => XWindowType::Utility,
+                egui::X11WindowType::Dock => XWindowType::Dock,
+                egui::X11WindowType::Desktop => XWindowType::Desktop,
+                egui::X11WindowType::Toolbar => XWindowType::Toolbar,
+                egui::X11WindowType::Menu => XWindowType::Menu,
+                egui::X11WindowType::Splash => XWindowType::Splash,
+                egui::X11WindowType::Dialog => XWindowType::Dialog,
+                egui::X11WindowType::DropdownMenu => XWindowType::DropdownMenu,
+                egui::X11WindowType::PopupMenu => XWindowType::PopupMenu,
+                egui::X11WindowType::Tooltip => XWindowType::Tooltip,
+                egui::X11WindowType::Notification => XWindowType::Notification,
+                egui::X11WindowType::Combo => XWindowType::Combo,
+                egui::X11WindowType::Dnd => XWindowType::Dnd,
+            }]);
+        }
+    }
+
     #[cfg(target_os = "windows")]
     {
         use winit::platform::windows::WindowBuilderExtWindows as _;

crates/egui/src/viewport.rs

@@ -301,6 +301,9 @@ pub struct ViewportBuilder {
     pub window_level: Option<WindowLevel>,
 
     pub mouse_passthrough: Option<bool>,
+
+    // X11
+    pub window_type: Option<X11WindowType>,
 }
 
 impl ViewportBuilder {
@@ -583,6 +586,15 @@ impl ViewportBuilder {
         self
     }
 
+    /// ### On X11
+    /// This sets the window type.
+    /// Maps directly to [`_NET_WM_WINDOW_TYPE`](https://specifications.freedesktop.org/wm-spec/wm-spec-1.5.html).
+    #[inline]
+    pub fn with_window_type(mut self, value: X11WindowType) -> Self {
+        self.window_type = Some(value);
+        self
+    }
+
     /// Update this `ViewportBuilder` with a delta,
     /// returning a list of commands and a bool indicating if the window needs to be recreated.
     #[must_use]
@@ -613,6 +625,7 @@ impl ViewportBuilder {
             window_level: new_window_level,
             mouse_passthrough: new_mouse_passthrough,
             taskbar: new_taskbar,
+            window_type: new_window_type,
         } = new_vp_builder;
 
         let mut commands = Vec::new();
@@ -786,6 +799,11 @@ impl ViewportBuilder {
             recreate_window = true;
         }
 
+        if new_window_type.is_some() && self.window_type != new_window_type {
+            self.window_type = new_window_type;
+            recreate_window = true;
+        }
+
         (commands, recreate_window)
     }
 }
@@ -799,6 +817,61 @@ pub enum WindowLevel {
     AlwaysOnTop,
 }
 
+#[derive(Clone, Copy, Debug, Default, PartialEq, Eq)]
+#[cfg_attr(feature = "serde", derive(serde::Deserialize, serde::Serialize))]
+pub enum X11WindowType {
+    /// This is a normal, top-level window.
+    #[default]
+    Normal,
+
+    /// A desktop feature. This can include a single window containing desktop icons with the same dimensions as the
+    /// screen, allowing the desktop environment to have full control of the desktop, without the need for proxying
+    /// root window clicks.
+    Desktop,
+
+    /// A dock or panel feature. Typically a Window Manager would keep such windows on top of all other windows.
+    Dock,
+
+    /// Toolbar windows. "Torn off" from the main application.
+    Toolbar,
+
+    /// Pinnable menu windows. "Torn off" from the main application.
+    Menu,
+
+    /// A small persistent utility window, such as a palette or toolbox.
+    Utility,
+
+    /// The window is a splash screen displayed as an application is starting up.
+    Splash,
+
+    /// This is a dialog window.
+    Dialog,
+
+    /// A dropdown menu that usually appears when the user clicks on an item in a menu bar.
+    /// This property is typically used on override-redirect windows.
+    DropdownMenu,
+
+    /// A popup menu that usually appears when the user right clicks on an object.
+    /// This property is typically used on override-redirect windows.
+    PopupMenu,
+
+    /// A tooltip window. Usually used to show additional information when hovering over an object with the cursor.
+    /// This property is typically used on override-redirect windows.
+    Tooltip,
+
+    /// The window is a notification.
+    /// This property is typically used on override-redirect windows.
+    Notification,
+
+    /// This should be used on the windows that are popped up by combo boxes.
+    /// This property is typically used on override-redirect windows.
+    Combo,
+
+    /// This indicates the the window is being dragged.
+    /// This property is typically used on override-redirect windows.
+    Dnd,
+}
+
 #[derive(Clone, Copy, Default, Debug, PartialEq, Eq)]
 #[cfg_attr(feature = "serde", derive(serde::Deserialize, serde::Serialize))]
 pub enum IMEPurpose {