Implement reactive-rendering for slider

widget/src/slider.rs

@@ -37,6 +37,7 @@ use crate::core::mouse;
 use crate::core::renderer;
 use crate::core::touch;
 use crate::core::widget::tree::{self, Tree};
+use crate::core::window;
 use crate::core::{
     self, Background, Clipboard, Color, Element, Layout, Length, Pixels, Point,
     Rectangle, Shell, Size, Theme, Widget,
@@ -95,6 +96,7 @@ where
     width: Length,
     height: f32,
     class: Theme::Class<'a>,
+    status: Option<Status>,
 }
 
 impl<'a, T, Message, Theme> Slider<'a, T, Message, Theme>
@@ -141,6 +143,7 @@ where
             width: Length::Fill,
             height: Self::DEFAULT_HEIGHT,
             class: Theme::default(),
+            status: None,
         }
     }
 
@@ -253,11 +256,12 @@ where
     ) -> event::Status {
         let state = tree.state.downcast_mut::<State>();
 
-        let is_dragging = state.is_dragging;
+        let mut update = || {
             let current_value = self.value;
 
             let locate = |cursor_position: Point| -> Option<T> {
                 let bounds = layout.bounds();
+
                 let new_value = if cursor_position.x <= bounds.x {
                     Some(*self.range.start())
                 } else if cursor_position.x >= bounds.x + bounds.width {
@@ -329,8 +333,10 @@ where
                 }
             };
 
-        match event {
-            Event::Mouse(mouse::Event::ButtonPressed(mouse::Button::Left))
+            match &event {
+                Event::Mouse(mouse::Event::ButtonPressed(
+                    mouse::Button::Left,
+                ))
                 | Event::Touch(touch::Event::FingerPressed { .. }) => {
                     if let Some(cursor_position) =
                         cursor.position_over(layout.bounds())
@@ -346,10 +352,12 @@ where
                         return event::Status::Captured;
                     }
                 }
-            Event::Mouse(mouse::Event::ButtonReleased(mouse::Button::Left))
+                Event::Mouse(mouse::Event::ButtonReleased(
+                    mouse::Button::Left,
+                ))
                 | Event::Touch(touch::Event::FingerLifted { .. })
                 | Event::Touch(touch::Event::FingerLost { .. }) => {
-                if is_dragging {
+                    if state.is_dragging {
                         if let Some(on_release) = self.on_release.clone() {
                             shell.publish(on_release);
                         }
@@ -360,7 +368,7 @@ where
                 }
                 Event::Mouse(mouse::Event::CursorMoved { .. })
                 | Event::Touch(touch::Event::FingerMoved { .. }) => {
-                if is_dragging {
+                    if state.is_dragging {
                         let _ = cursor.position().and_then(locate).map(change);
 
                         return event::Status::Captured;
@@ -375,7 +383,7 @@ where
                             mouse::ScrollDelta::Pixels { x: _, y } => y,
                         };
 
-                    if delta < 0.0 {
+                        if *delta < 0.0 {
                             let _ = decrement(current_value).map(change);
                         } else {
                             let _ = increment(current_value).map(change);
@@ -384,7 +392,9 @@ where
                         return event::Status::Captured;
                     }
                 }
-            Event::Keyboard(keyboard::Event::KeyPressed { key, .. }) => {
+                Event::Keyboard(keyboard::Event::KeyPressed {
+                    key, ..
+                }) => {
                     if cursor.is_over(layout.bounds()) {
                         match key {
                             Key::Named(key::Named::ArrowUp) => {
@@ -399,39 +409,55 @@ where
                         return event::Status::Captured;
                     }
                 }
-            Event::Keyboard(keyboard::Event::ModifiersChanged(modifiers)) => {
-                state.keyboard_modifiers = modifiers;
+                Event::Keyboard(keyboard::Event::ModifiersChanged(
+                    modifiers,
+                )) => {
+                    state.keyboard_modifiers = *modifiers;
                 }
                 _ => {}
             }
 
             event::Status::Ignored
+        };
+
+        let update_status = update();
+
+        let current_status = if state.is_dragging {
+            Status::Dragged
+        } else if cursor.is_over(layout.bounds()) {
+            Status::Hovered
+        } else {
+            Status::Active
+        };
+
+        if let Event::Window(window::Event::RedrawRequested(_now)) = event {
+            self.status = Some(current_status);
+        } else {
+            match self.status {
+                Some(status) if status != current_status => {
+                    shell.request_redraw(window::RedrawRequest::NextFrame);
+                }
+                _ => {}
+            }
+        }
+
+        update_status
     }
 
     fn draw(
         &self,
-        tree: &Tree,
+        _tree: &Tree,
         renderer: &mut Renderer,
         theme: &Theme,
         _style: &renderer::Style,
         layout: Layout<'_>,
-        cursor: mouse::Cursor,
+        _cursor: mouse::Cursor,
         _viewport: &Rectangle,
     ) {
-        let state = tree.state.downcast_ref::<State>();
         let bounds = layout.bounds();
-        let is_mouse_over = cursor.is_over(bounds);
 
-        let style = theme.style(
-            &self.class,
-            if state.is_dragging {
-                Status::Dragged
-            } else if is_mouse_over {
-                Status::Hovered
-            } else {
-                Status::Active
-            },
-        );
+        let style =
+            theme.style(&self.class, self.status.unwrap_or(Status::Active));
 
         let (handle_width, handle_height, handle_border_radius) =
             match style.handle.shape {

winit/src/program.rs

@@ -1161,6 +1161,8 @@ async fn run_instance<P, C>(
                         }
 
                         if !redraw_queue.is_empty() {
+                            // The queue should be fairly short, so we can
+                            // simply sort all of the time.
                             redraw_queue.sort_by(
                                 |(target_a, _), (target_b, _)| {
                                     target_a.cmp(target_b).reverse()