Fill the windows in the examples with a solid color

Fixes #776.

examples/request_redraw_threaded.rs

@@ -2,7 +2,7 @@
 
 #[cfg(not(wasm_platform))]
 fn main() {
-    use std::{thread, time};
+    use std::{sync::Arc, thread, time};
 
     use simple_logger::SimpleLogger;
     use winit::{
@@ -11,17 +11,26 @@ fn main() {
         window::WindowBuilder,
     };
 
+    #[path = "util/fill.rs"]
+    mod fill;
+
     SimpleLogger::new().init().unwrap();
     let event_loop = EventLoop::new();
 
-    let window = WindowBuilder::new()
-        .with_title("A fantastic window!")
-        .build(&event_loop)
-        .unwrap();
+    let window = {
+        let window = WindowBuilder::new()
+            .with_title("A fantastic window!")
+            .build(&event_loop)
+            .unwrap();
+        Arc::new(window)
+    };
 
-    thread::spawn(move || loop {
-        thread::sleep(time::Duration::from_secs(1));
-        window.request_redraw();
+    thread::spawn({
+        let window = window.clone();
+        move || loop {
+            thread::sleep(time::Duration::from_secs(1));
+            window.request_redraw();
+        }
     });
 
     event_loop.run(move |event, _, control_flow| {
@@ -36,6 +45,7 @@ fn main() {
             } => control_flow.set_exit(),
             Event::RedrawRequested(_) => {
                 println!("\nredrawing!\n");
+                fill::fill_window(&window);
             }
             _ => (),
         }