feat(progress_bar): animate determinate progress

src/widget/progress_bar/animation.rs

@@ -2,6 +2,39 @@ use crate::anim::smootherstep;
 use iced::time::Instant;
 use std::time::Duration;
 
+const LAG: f32 = 0.1;
+
+pub struct Progress {
+    pub current: f32,
+    last: Instant,
+}
+
+impl Default for Progress {
+    fn default() -> Self {
+        Self {
+            current: 0.0,
+            last: Instant::now(),
+        }
+    }
+}
+
+impl Progress {
+    /// Smoothly chases `target` using exponential decay.
+    /// Returns `true` if still animating and a redraw should be requested.
+    pub fn update(&mut self, target: f32, now: Instant) -> bool {
+        let dt = (now - self.last).as_secs_f32();
+        self.last = now;
+        let next = self.current + (target - self.current) * (1.0 - (-dt / LAG).exp());
+        if (next - target).abs() > 0.001 {
+            self.current = next;
+            true
+        } else {
+            self.current = target;
+            false
+        }
+    }
+}
+
 #[derive(Clone, Copy)]
 pub struct Animation {
     expanding: bool,
@@ -26,12 +59,12 @@ impl Animation {
     pub fn timed_transition(
         &self,
         cycle_duration: Duration,
-        rotation_duration: Duration,
+        period: Duration,
         wrap: f32,
         now: Instant,
     ) -> Self {
-        let additional = ((now - self.last).as_secs_f32() / rotation_duration.as_secs_f32()
-            * u32::MAX as f32) as u32;
+        let additional =
+            ((now - self.last).as_secs_f32() / period.as_secs_f32() * u32::MAX as f32) as u32;
         let new_offset = self.offset.wrapping_add(additional);
 
         if !cycle_duration.is_zero() && now.duration_since(self.start) > cycle_duration {

src/widget/progress_bar/circular.rs

@@ -1,5 +1,5 @@
 //! Show a circular progress indicator.
-use super::animation::Animation;
+use super::animation::{Animation, Progress};
 use super::style::StyleSheet;
 use iced::advanced::layout;
 use iced::advanced::renderer;
@@ -24,7 +24,7 @@ where
     bar_height: f32,
     style: Theme::Style,
     cycle_duration: Duration,
-    rotation_duration: Duration,
+    period: Duration,
     progress: Option<f32>,
 }
 
@@ -39,7 +39,7 @@ where
             bar_height: 4.0,
             style: Theme::Style::default(),
             cycle_duration: Duration::from_millis(1500),
-            rotation_duration: Duration::from_secs(2),
+            period: Duration::from_secs(2),
             progress: None,
         }
     }
@@ -68,10 +68,10 @@ where
         self
     }
 
-    /// Sets the base rotation duration of this [`Circular`]. This is the duration that a full
-    /// rotation would take if the cycle duration were set to 0.0 (no expanding or contracting)
-    pub fn rotation_duration(mut self, duration: Duration) -> Self {
-        self.rotation_duration = duration;
+    /// Sets the base period of this [`Circular`]. This is the duration that a full rotation
+    /// would take if the cycle duration were set to 0.0 (no expanding or contracting)
+    pub fn period(mut self, duration: Duration) -> Self {
+        self.period = duration;
         self
     }
 
@@ -101,7 +101,7 @@ where
 struct State {
     animation: Animation,
     cache: canvas::Cache,
-    progress: Option<f32>,
+    progress: Progress,
 }
 
 impl<Message, Theme> Widget<Message, Theme, Renderer> for Circular<Theme>
@@ -145,23 +145,21 @@ where
         _viewport: &Rectangle,
     ) {
         let state = tree.state.downcast_mut::<State>();
-        if self.progress.is_some() {
-            if state.progress != self.progress {
-                state.progress = self.progress;
-                state.cache.clear();
-            }
-            return;
-        }
         if let Event::Window(window::Event::RedrawRequested(now)) = event {
-            let (_, wrap) = self.min_wrap(self.size / 2.0 - self.bar_height);
-            state.animation = state.animation.timed_transition(
-                self.cycle_duration,
-                self.rotation_duration,
-                wrap,
-                *now,
-            );
-            state.cache.clear();
-            shell.request_redraw();
+            if let Some(target) = self.progress {
+                if state.progress.update(target, *now) {
+                    state.cache.clear();
+                    shell.request_redraw();
+                }
+            } else {
+                let (_, wrap) = self.min_wrap(self.size / 2.0 - self.bar_height);
+                state.animation =
+                    state
+                        .animation
+                        .timed_transition(self.cycle_duration, self.period, wrap, *now);
+                state.cache.clear();
+                shell.request_redraw();
+            }
         }
     }
 
@@ -231,7 +229,7 @@ where
                 draw_cap(frame, start, true);
             };
 
-            if let Some(progress) = self.progress {
+            if self.progress.is_some() {
                 if let Some(border_color) = custom_style.border_color {
                     for radius_offset in [self.bar_height / 2.0, -(self.bar_height / 2.0)] {
                         let border_path =
@@ -244,7 +242,7 @@ where
                         );
                     }
                 }
-                draw_bar(frame, 0.0, progress);
+                draw_bar(frame, 0.0, state.progress.current);
             } else {
                 let (min, wrap) = self.min_wrap(track_radius);
                 let (start, end) = state

src/widget/progress_bar/linear.rs

@@ -1,5 +1,5 @@
 //! Show a linear progress indicator.
-use super::animation::Animation;
+use super::animation::{Animation, Progress};
 use super::style::StyleSheet;
 use iced::advanced::layout;
 use iced::advanced::renderer;
@@ -23,7 +23,7 @@ where
     girth: Length,
     style: Theme::Style,
     cycle_duration: Duration,
-    traversal_duration: Duration,
+    period: Duration,
     progress: Option<f32>,
 }
 
@@ -38,7 +38,7 @@ where
             girth: Length::Fixed(4.0),
             style: Theme::Style::default(),
             cycle_duration: Duration::from_millis(1500),
-            traversal_duration: Duration::from_secs(2),
+            period: Duration::from_secs(2),
             progress: None,
         }
     }
@@ -67,10 +67,10 @@ where
         self
     }
 
-    /// Sets the base traversal duration of this [`Linear`]. This is the duration that a full
-    /// traversal would take if the cycle duration were set to 0.0 (no expanding or contracting)
-    pub fn traversal_duration(mut self, duration: Duration) -> Self {
-        self.traversal_duration = duration;
+    /// Sets the base period of this [`Linear`]. This is the duration that a full traversal
+    /// would take if the cycle duration were set to 0.0 (no expanding or contracting)
+    pub fn period(mut self, duration: Duration) -> Self {
+        self.period = duration;
         self
     }
 
@@ -90,6 +90,12 @@ where
     }
 }
 
+#[derive(Default)]
+struct State {
+    animation: Animation,
+    progress: Progress,
+}
+
 impl<Message, Theme, Renderer> Widget<Message, Theme, Renderer> for Linear<Theme>
 where
     Message: Clone,
@@ -97,11 +103,11 @@ where
     Renderer: advanced::Renderer,
 {
     fn tag(&self) -> tree::Tag {
-        tree::Tag::of::<Animation>()
+        tree::Tag::of::<State>()
     }
 
     fn state(&self) -> tree::State {
-        tree::State::new(Animation::default())
+        tree::State::new(State::default())
     }
 
     fn size(&self) -> Size<Length> {
@@ -131,20 +137,21 @@ where
         shell: &mut Shell<'_, Message>,
         _viewport: &Rectangle,
     ) {
-        if self.progress.is_some() {
-            return;
-        }
-
-        let animation = tree.state.downcast_mut::<Animation>();
-
+        let state = tree.state.downcast_mut::<State>();
         if let Event::Window(window::Event::RedrawRequested(now)) = event {
-            *animation = animation.timed_transition(
-                self.cycle_duration,
-                self.traversal_duration,
-                WRAP_LENGTH,
-                *now,
-            );
-            shell.request_redraw();
+            if let Some(target) = self.progress {
+                if state.progress.update(target, *now) {
+                    shell.request_redraw();
+                }
+            } else {
+                state.animation = state.animation.timed_transition(
+                    self.cycle_duration,
+                    self.period,
+                    WRAP_LENGTH,
+                    *now,
+                );
+                shell.request_redraw();
+            }
         }
     }
 
@@ -160,7 +167,7 @@ where
     ) {
         let bounds = layout.bounds();
         let custom_style = theme.appearance(&self.style, self.progress.is_some(), false);
-        let animation = tree.state.downcast_ref::<Animation>();
+        let state = tree.state.downcast_ref::<State>();
 
         renderer.fill_quad(
             renderer::Quad {
@@ -203,11 +210,13 @@ where
             }
         };
 
-        if let Some(progress) = self.progress {
-            draw_segment(0.0, progress);
+        if self.progress.is_some() {
+            draw_segment(0.0, state.progress.current);
         } else {
             let (bar_start, bar_end) =
-                animation.bar_positions(self.cycle_duration, MIN_LENGTH, WRAP_LENGTH);
+                state
+                    .animation
+                    .bar_positions(self.cycle_duration, MIN_LENGTH, WRAP_LENGTH);
             let length = bar_end - bar_start;
             let start = bar_start % 1.0;
             let right_width = (1.0 - start).min(length);