Added is_desktop checkbox in egui_demo_app

Fix window not rendering if is_desktop is false

crates/egui/src/containers/window.rs

@@ -469,7 +469,7 @@ impl<'open> Window<'open> {
         // let is_explicitly_closed = matches!(open, Some(false));
         let is_open = is_open || ctx.memory(|mem| mem.everything_is_visible());
         'create_viewport: {
-            if !embedded {
+            if !embedded && ctx.is_desktop() {
                 if !is_open {
                     return;
                 }

crates/egui_demo_app/src/backend_panel.rs

@@ -173,6 +173,11 @@ impl BackendPanel {
                         frame.set_fullscreen(fullscreen);
                     }
                 }
+                {
+                    let mut is_desktop = ui.ctx().is_desktop();
+                    ui.checkbox(&mut is_desktop, "Is Desktop");
+                    ui.ctx().set_desktop(is_desktop);
+                }
 
                 if ui
                     .button("📱 Phone Size")