One proxy, and a macro instead of a shared test module

`Proxy` is the task queue as well as the way an application sends its own
events, so `ProxyQueue` is gone. `schedule_redraw` becomes
`request_redraw_if_needed`, which says what the comment beside it was
saying.

`assert_corners!` replaces the region helper, so `tests/common` goes with
it, and the scroll test now states both corners rather than one number.

src/default/mod.rs

@@ -49,9 +49,7 @@ pub enum DefaultEvent<State: DefaultAppState> {
     Update(Box<dyn TaskUpdate<DefaultRsc<State>>>),
 }
 
-struct ProxyQueue<State: DefaultAppState>(EventLoopProxy<DefaultEvent<State>>);
-
-impl<State: DefaultAppState> TaskQueue<DefaultRsc<State>> for ProxyQueue<State> {
+impl<State: DefaultAppState> TaskQueue<DefaultRsc<State>> for Proxy<State> {
     fn send(&self, update: Box<dyn TaskUpdate<DefaultRsc<State>>>) {
         let _ = self.0.send_event(DefaultEvent::Update(update));
     }
@@ -212,7 +210,7 @@ impl<State: DefaultAppState> AppState for DefaultApp<State> {
             .create_window(State::window_attributes())
             .unwrap();
         let default_state = DefaultUiState::new(window);
-        let mut rsc = DefaultRsc::init(Arc::new(ProxyQueue(proxy.clone())));
+        let mut rsc = DefaultRsc::init(Arc::new(Proxy(proxy.clone())));
         let state = State::new(default_state, &mut rsc, Proxy(proxy));
         let render = UiRenderState::new();
         Self { rsc, state, render }
@@ -223,9 +221,7 @@ impl<State: DefaultAppState> AppState for DefaultApp<State> {
             DefaultEvent::User(event) => self.state.event(event, &mut self.rsc, &mut self.render),
             DefaultEvent::Update(update) => update(&mut self.state, &mut self.rsc),
         }
-        // An update is not a reason to draw; whether it made anything dirty
-        // is. That is why a task posts here rather than asking for a redraw.
-        self.schedule_redraw();
+        self.request_redraw_if_needed();
     }
 
     fn window_event(&mut self, event: WindowEvent, event_loop: &ActiveEventLoop) {
@@ -309,7 +305,7 @@ impl<State: DefaultAppState> AppState for DefaultApp<State> {
             _ => (),
         }
         state.window_event(event, rsc, render);
-        self.schedule_redraw();
+        self.request_redraw_if_needed();
         self.state.default_state_mut().input.end_frame();
     }
 
@@ -319,7 +315,7 @@ impl<State: DefaultAppState> AppState for DefaultApp<State> {
 }
 
 impl<State: DefaultAppState> DefaultApp<State> {
-    fn schedule_redraw(&mut self) {
+    fn request_redraw_if_needed(&mut self) {
         let ui_state = self.state.default_state_mut();
         if self.render.needs_redraw(&ui_state.root, self.rsc.widgets()) {
             ui_state.renderer.window().request_redraw();

src/harness.rs

@@ -22,6 +22,25 @@ impl TaskQueue<DefaultRsc<HarnessState>> for Queue {
     }
 }
 
+/// `assert_eq!` for where a frame put a widget, which `PixelRegion` cannot do
+/// for itself: it neither compares nor prints.
+#[macro_export]
+macro_rules! assert_corners {
+    ($harness:expr, $id:expr, ($x0:expr, $y0:expr), ($x1:expr, $y1:expr)) => {{
+        let region = $harness.region(&$id).expect("widget drew nothing");
+        assert_eq!(
+            (
+                region.top_left.x,
+                region.top_left.y,
+                region.bot_right.x,
+                region.bot_right.y
+            ),
+            ($x0 as f32, $y0 as f32, $x1 as f32, $y1 as f32)
+        );
+    }};
+}
+pub use crate::assert_corners;
+
 #[derive(Default)]
 pub struct HarnessState {
     pub root: Option<StrongWidget>,