* Now: is_desktop can only be set at the creation with egui::Context::new insted of default!

* Removed: egui::Context::is_desktop, egui::Context::set_desktop
* Added: egui::Context::force_embedding, egui::Context::set_force_embedding

crates/eframe/src/native/epi_integration.rs

@@ -333,10 +333,11 @@ impl EpiIntegration {
         app_name: &str,
         native_options: &crate::NativeOptions,
         storage: Option<Box<dyn epi::Storage>>,
+        desktop: bool,
         #[cfg(feature = "glow")] gl: Option<std::sync::Arc<glow::Context>>,
         #[cfg(feature = "wgpu")] wgpu_render_state: Option<egui_wgpu::RenderState>,
     ) -> Self {
-        let egui_ctx = egui::Context::default();
+        let egui_ctx = egui::Context::new(desktop);
 
         let memory = load_egui_memory(storage.as_deref()).unwrap_or_default();
         egui_ctx.memory_mut(|mem| *mem = memory);

crates/eframe/src/native/run.rs

@@ -19,6 +19,16 @@ use super::epi_integration::{self, EpiIntegration};
 
 // ----------------------------------------------------------------------------
 
+pub const IS_DESKTOP: bool = cfg!(any(
+    target_os = "windows",
+    target_os = "linux",
+    target_os = "macos",
+    target_os = "freebsd",
+    target_os = "openbsd"
+));
+
+// ----------------------------------------------------------------------------
+
 #[derive(Debug)]
 pub enum UserEvent {
     RequestRepaint {
@@ -891,6 +901,7 @@ mod glow_integration {
                 &self.app_name,
                 &self.native_options,
                 storage,
+                IS_DESKTOP,
                 Some(gl.clone()),
                 #[cfg(feature = "wgpu")]
                 None,
@@ -908,12 +919,6 @@ mod glow_integration {
             let theme = system_theme.unwrap_or(self.native_options.default_theme);
             integration.egui_ctx.set_visuals(theme.egui_visuals());
 
-            // !!! WARNING This is needed to be improved !!!
-            // I don't really know not to detect if is on desktop or web/mobile
-            // This allows to have multiples windows
-
-            integration.egui_ctx.set_desktop(true);
-
             gl_window
                 .window(ViewportId::MAIN)
                 .read()
@@ -1885,6 +1890,7 @@ mod wgpu_integration {
                 &self.app_name,
                 &self.native_options,
                 storage,
+                IS_DESKTOP,
                 #[cfg(feature = "glow")]
                 None,
                 wgpu_render_state.clone(),

crates/egui/src/containers/window.rs

@@ -365,7 +365,7 @@ impl<'open> Window<'open> {
         let show_close_button = open.is_some();
 
         'create_viewport: {
-            if !is_embedded && ctx.is_desktop() {
+            if !is_embedded && !ctx.force_embedding() {
                 if let Some(size) = ctx.data(|data| data.get_temp::<Vec2>(area.id.with("size"))) {
                     let size = size.round()
                         + ctx.style().spacing.window_margin.sum() * ctx.pixels_per_point();
@@ -822,7 +822,7 @@ impl<'open> Window<'open> {
         let show_close_button = open.is_some();
 
         'create_viewport: {
-            if !is_embedded && ctx.is_desktop() {
+            if !is_embedded && !ctx.force_embedding() {
                 if let Some(size) = ctx.data(|data| data.get_temp::<Vec2>(area.id.with("size"))) {
                     let size = size.round()
                         + ctx.style().spacing.window_margin.sum() * ctx.pixels_per_point();

crates/egui/src/context.rs

@@ -224,6 +224,7 @@ struct ContextImpl {
 
     viewport_counter: u64,
     is_desktop: bool,
+    force_embedding: bool,
 
     /// Written to during the frame.
     layer_rects_this_frame: ahash::HashMap<LayerId, Vec<(Id, Rect)>>,
@@ -469,6 +470,7 @@ impl Default for Context {
         let clone = s.clone();
 
         s.write(|ctx| {
+            ctx.force_embedding = true;
             ctx.render_sync = Some(Arc::new(Box::new(
                 move |_builder, _viewport_id, _parent_viewport_id, render| render(&clone),
             )));
@@ -549,6 +551,15 @@ impl Context {
     ) {
         self.write(|ctx| ctx.begin_frame_mut(new_input, viewport_id, parent_viewport_id));
     }
+
+    pub fn new(desktop: bool) -> Context {
+        let context = Context::default();
+        context.write(|ctx| {
+            ctx.is_desktop = desktop;
+            ctx.force_embedding = !desktop;
+        });
+        context
+    }
 }
 
 /// ## Borrows parts of [`Context`]
@@ -2202,16 +2213,15 @@ impl Context {
         self.write(|ctx| ctx.render_sync = Some(Arc::new(callback)));
     }
 
-    /// This will tell you if the app can create multiples native windows
+    /// If this is true no other native windows will be created
-    pub fn is_desktop(&self) -> bool {
+    pub fn force_embedding(&self) -> bool {
-        self.read(|ctx| ctx.is_desktop)
+        self.read(|ctx| ctx.force_embedding)
     }
 
-    /// This should only be called with value true by the backend!
+    /// If this is true no other native windows, will not be created for a ```egui::Window``` or Viewport
-    ///
+    /// You will always be able to set to false
-    /// With this you can tell egui that is able to open multiples native windows
+    pub fn set_force_embedding(&self, value: bool) {
-    pub fn set_desktop(&self, value: bool) {
+        self.write(|ctx| ctx.force_embedding = value || !ctx.is_desktop);
-        self.write(|ctx| ctx.is_desktop = value);
     }
 
     /// With this you can send a command to a viewport
@@ -2230,7 +2240,7 @@ impl Context {
         viewport_builder: ViewportBuilder,
         render: impl Fn(&Context) + Send + Sync + 'static,
     ) {
-        if self.is_desktop() {
+        if !self.force_embedding() {
             self.write(|ctx| {
                 let viewport_id = ctx.get_viewport_id();
                 if let Some(window) = ctx.viewports.get_mut(&viewport_builder.title) {
@@ -2269,7 +2279,7 @@ impl Context {
         viewport_builder: ViewportBuilder,
         func: impl FnOnce(&Context) -> T,
     ) -> T {
-        if self.is_desktop() {
+        if !self.force_embedding() {
             let mut viewport_id = ViewportId::MAIN;
             let mut parent_viewport_id = ViewportId::MAIN;
             let render_sync = self.write(|ctx| {

crates/egui_demo_app/src/backend_panel.rs

@@ -172,9 +172,9 @@ impl BackendPanel {
                     }
                 }
                 {
-                    let mut is_desktop = ui.ctx().is_desktop();
+                    let mut force_embedding = ui.ctx().force_embedding();
-                    ui.checkbox(&mut is_desktop, "Is Desktop");
+                    ui.checkbox(&mut force_embedding, "Force Embedding");
-                    ui.ctx().set_desktop(is_desktop);
+                    ui.ctx().set_force_embedding(force_embedding);
                 }
 
                 if ui

examples/viewports/src/main.rs

@@ -48,9 +48,9 @@ impl eframe::App for App {
             ui.label(format!("Size: {:?}", ctx.screen_rect().max));
             ui.label("Look at the \"Frame: \" will tell you, what viewport is rendering!");
             {
-                let mut desktop = ctx.is_desktop();
+                let mut force_embedding = ctx.force_embedding();
-                ui.checkbox(&mut desktop, "Desktop");
+                ui.checkbox(&mut force_embedding, "Force embedding!");
-                ctx.set_desktop(desktop);
+                ctx.set_force_embedding(force_embedding);
             }
             ui.checkbox(&mut self.show_async_viewport, "Show Async Viewport");
             ui.checkbox(&mut self.show_sync_viewport, "Show Sync Viewport");