WIP: Add test/example code for child windows

Author: t-sin

examples/child_window.rs

@@ -0,0 +1,53 @@
+use simple_logger::SimpleLogger;
+use winit::{
+    event::{ElementState, Event, KeyboardInput, WindowEvent},
+    event_loop::{ControlFlow, EventLoop},
+    window::Window,
+};
+
+#[cfg(feature = "x11")]
+use winit::platform::unix::{EventLoopExtUnix, WindowExtUnix};
+
+#[cfg(feature = "x11")]
+fn main() {
+    SimpleLogger::new().init().unwrap();
+    let event_loop = EventLoop::new_x11_any_thread().unwrap();
+    let parent_window = Window::new(&event_loop).unwrap();
+    let root = parent_window.xlib_window().unwrap();
+    println!("root (id: {})", root);
+
+    event_loop.run(move |event: Event<'_, ()>, _, control_flow| {
+        *control_flow = ControlFlow::Wait;
+
+        match event {
+            Event::WindowEvent {
+                event,
+                window_id: _,
+            } => match event {
+                WindowEvent::CloseRequested => {
+                    *control_flow = ControlFlow::Exit;
+                }
+                WindowEvent::KeyboardInput {
+                    input:
+                        KeyboardInput {
+                            state: ElementState::Pressed,
+                            ..
+                        },
+                    ..
+                } => {
+                    let root = parent_window.xlib_window().unwrap() as u32;
+                    let child_event_loop: EventLoop<()> =
+                        EventLoop::new_x11_any_thread_with_root(root.into()).unwrap();
+                    Window::new(&child_event_loop).unwrap();
+                }
+                _ => (),
+            },
+            _ => (),
+        }
+    })
+}
+
+#[cfg(not(feature = "x11"))]
+fn main() {
+    panic!("This example is supported only on x11.");
+}