feat: use lyon for easing

examples/loading_spinners/src/circular.rs

@@ -0,0 +1,444 @@
+//! Show a circular progress indicator.
+use iced::widget::canvas::{self, Cursor, Program, Renderer as CanvasRenderer};
+use iced::window;
+use iced_core::event::{self, Event};
+use iced_core::time::Instant;
+use iced_core::widget::tree::{self, Tree};
+use iced_core::window::RedrawRequest;
+use iced_core::{layout, Size};
+use iced_core::{renderer, Vector};
+use iced_core::{
+    Background, Clipboard, Color, Element, Layout, Length, Point, Rectangle,
+    Renderer, Shell, Widget,
+};
+
+use super::easing::{self, Easing};
+
+use std::f32::consts::PI;
+use std::time::Duration;
+
+type R<Theme> = iced_widget::renderer::Renderer<Theme>;
+
+const MIN_RADIANS: f32 = PI / 8.0;
+const WRAP_RADIANS: f32 = 2.0 * PI - PI / 4.0;
+const BASE_ROTATION_SPEED: u32 = u32::MAX / 80;
+
+#[allow(missing_debug_implementations)]
+pub struct Circular<'a, Theme>
+where
+    Theme: StyleSheet,
+{
+    size: f32,
+    bar_height: f32,
+    style: <Theme as StyleSheet>::Style,
+    easing: &'a Easing,
+    cycle_duration: Duration,
+    rotation_speed: u32,
+}
+
+impl<'a, Theme> Circular<'a, Theme>
+where
+    Theme: StyleSheet,
+{
+    /// Creates a new [`Circular`] with the given content.
+    pub fn new() -> Self {
+        Circular {
+            size: 40.0,
+            bar_height: 4.0,
+            style: <Theme as StyleSheet>::Style::default(),
+            easing: &easing::STANDARD,
+            cycle_duration: Duration::from_millis(600),
+            rotation_speed: BASE_ROTATION_SPEED,
+        }
+    }
+
+    /// Sets the size of the [`Circular`].
+    pub fn size(mut self, size: f32) -> Self {
+        self.size = size;
+        self
+    }
+
+    /// Sets the bar height of the [`Circular`].
+    pub fn bar_height(mut self, bar_height: f32) -> Self {
+        self.bar_height = bar_height;
+        self
+    }
+
+    /// Sets the style variant of this [`Circular`].
+    pub fn style(mut self, style: <Theme as StyleSheet>::Style) -> Self {
+        self.style = style;
+        self
+    }
+
+    /// Sets the easing of this [`Circular`].
+    pub fn easing(mut self, easing: &'a Easing) -> Self {
+        self.easing = easing;
+        self
+    }
+
+    /// Sets the cycle duration of this [`Circular`].
+    pub fn cycle_duration(mut self, duration: Duration) -> Self {
+        self.cycle_duration = duration / 2;
+        self
+    }
+
+    /// Sets the rotation speed of this [`Circular`]. Must be set to between 0.0 and 10.0.
+    /// Defaults to 1.0.
+    pub fn rotation_speed(mut self, speed: f32) -> Self {
+        let multiplier = speed.min(10.0).max(0.0);
+        self.rotation_speed = (BASE_ROTATION_SPEED as f32 * multiplier) as u32;
+        self
+    }
+}
+
+impl<'a, Theme> Default for Circular<'a, Theme>
+where
+    Theme: StyleSheet,
+{
+    fn default() -> Self {
+        Self::new()
+    }
+}
+
+#[derive(Clone, Copy)]
+enum State {
+    Expanding {
+        start: Instant,
+        progress: f32,
+        procession: u32,
+    },
+    Contracting {
+        start: Instant,
+        progress: f32,
+        procession: u32,
+    },
+}
+
+impl Default for State {
+    fn default() -> Self {
+        Self::Expanding {
+            start: Instant::now(),
+            progress: 0.0,
+            procession: 0,
+        }
+    }
+}
+
+impl State {
+    fn next(&self, now: Instant) -> Self {
+        match self {
+            Self::Expanding { procession, .. } => Self::Contracting {
+                start: now,
+                progress: 0.0,
+                procession: procession.wrapping_add(BASE_ROTATION_SPEED),
+            },
+            Self::Contracting { procession, .. } => Self::Expanding {
+                start: now,
+                progress: 0.0,
+                procession: procession.wrapping_add(
+                    BASE_ROTATION_SPEED.wrapping_add(
+                        ((WRAP_RADIANS / (2.0 * PI)) * u32::MAX as f32) as u32,
+                    ),
+                ),
+            },
+        }
+    }
+
+    fn start(&self) -> Instant {
+        match self {
+            Self::Expanding { start, .. } | Self::Contracting { start, .. } => {
+                *start
+            }
+        }
+    }
+
+    fn timed_transition(
+        &self,
+        cycle_duration: Duration,
+        rotation_speed: u32,
+        now: Instant,
+    ) -> Self {
+        let elapsed = now.duration_since(self.start());
+
+        match elapsed {
+            elapsed if elapsed > cycle_duration => self.next(now),
+            _ => self.with_elapsed(cycle_duration, rotation_speed, elapsed),
+        }
+    }
+
+    fn with_elapsed(
+        &self,
+        cycle_duration: Duration,
+        rotation_speed: u32,
+        elapsed: Duration,
+    ) -> Self {
+        let progress = elapsed.as_secs_f32() / cycle_duration.as_secs_f32();
+        match self {
+            Self::Expanding {
+                start, procession, ..
+            } => Self::Expanding {
+                start: *start,
+                progress,
+                procession: procession.wrapping_add(rotation_speed),
+            },
+            Self::Contracting {
+                start, procession, ..
+            } => Self::Contracting {
+                start: *start,
+                progress,
+                procession: procession.wrapping_add(rotation_speed),
+            },
+        }
+    }
+
+    fn procession(&self) -> f32 {
+        match self {
+            Self::Expanding { procession, .. }
+            | Self::Contracting { procession, .. } => {
+                *procession as f32 / u32::MAX as f32
+            }
+        }
+    }
+}
+
+impl<'a, Message, Theme> Widget<Message, R<Theme>> for Circular<'a, Theme>
+where
+    Message: 'a + Clone,
+    Theme: StyleSheet,
+{
+    fn tag(&self) -> tree::Tag {
+        tree::Tag::of::<State>()
+    }
+
+    fn state(&self) -> tree::State {
+        tree::State::new(State::default())
+    }
+
+    fn width(&self) -> Length {
+        Length::Fixed(self.size)
+    }
+
+    fn height(&self) -> Length {
+        Length::Fixed(self.size)
+    }
+
+    fn layout(
+        &self,
+        _renderer: &iced_widget::renderer::Renderer<Theme>,
+        limits: &layout::Limits,
+    ) -> layout::Node {
+        let limits = limits.width(self.size).height(self.size);
+        let size = limits.resolve(Size::ZERO);
+
+        layout::Node::new(size)
+    }
+
+    fn on_event(
+        &mut self,
+        tree: &mut Tree,
+        event: Event,
+        _layout: Layout<'_>,
+        _cursor_position: Point,
+        _renderer: &iced_widget::renderer::Renderer<Theme>,
+        _clipboard: &mut dyn Clipboard,
+        shell: &mut Shell<'_, Message>,
+    ) -> event::Status {
+        let state = tree.state.downcast_mut::<State>();
+
+        if let Event::Window(window::Event::RedrawRequested(now)) = event {
+            *state = state.timed_transition(
+                self.cycle_duration,
+                self.rotation_speed,
+                now,
+            );
+
+            shell.request_redraw(RedrawRequest::NextFrame);
+        }
+
+        event::Status::Ignored
+    }
+
+    fn draw(
+        &self,
+        tree: &Tree,
+        renderer: &mut R<Theme>,
+        theme: &Theme,
+        _style: &renderer::Style,
+        layout: Layout<'_>,
+        _cursor_position: Point,
+        _viewport: &Rectangle,
+    ) {
+        let bounds = layout.bounds();
+        let state = tree.state.downcast_ref::<State>();
+
+        renderer.with_translation(
+            Vector::new(bounds.x, bounds.y),
+            |renderer| {
+                renderer.draw(<StateWithStyle<Theme> as Program<
+                    Message,
+                    R<Theme>,
+                >>::draw(
+                    &StateWithStyle {
+                        state,
+                        style: &self.style,
+                        bar_height: self.bar_height,
+                        easing: self.easing,
+                    },
+                    &(),
+                    renderer,
+                    theme,
+                    bounds,
+                    Cursor::Unavailable,
+                ));
+            },
+        );
+    }
+}
+
+impl<'a, Message, Theme> From<Circular<'a, Theme>>
+    for Element<'a, Message, R<Theme>>
+where
+    Message: Clone + 'a,
+    Theme: StyleSheet + 'a,
+{
+    fn from(circular: Circular<'a, Theme>) -> Self {
+        Self::new(circular)
+    }
+}
+
+#[derive(Debug, Clone, Copy)]
+pub struct Appearance {
+    /// The [`Background`] of the progress indicator.
+    pub background: Option<Background>,
+    /// The track [`Color`] of the progress indicator.
+    pub track_color: Color,
+    /// The bar [`Color`] of the progress indicator.
+    pub bar_color: Color,
+}
+
+impl std::default::Default for Appearance {
+    fn default() -> Self {
+        Self {
+            background: None,
+            track_color: Color::TRANSPARENT,
+            bar_color: Color::BLACK,
+        }
+    }
+}
+
+/// A set of rules that dictate the style of an indicator.
+pub trait StyleSheet {
+    /// The supported style of the [`StyleSheet`].
+    type Style: Default;
+
+    /// Produces the active [`Appearance`] of a indicator.
+    fn appearance(&self, style: &Self::Style) -> Appearance;
+}
+
+impl StyleSheet for iced::Theme {
+    type Style = ();
+
+    fn appearance(&self, _style: &Self::Style) -> Appearance {
+        let palette = self.extended_palette();
+
+        Appearance {
+            background: None,
+            track_color: palette.background.weak.color,
+            bar_color: palette.primary.base.color,
+        }
+    }
+}
+
+struct StateWithStyle<'a, Theme>
+where
+    Theme: StyleSheet,
+{
+    state: &'a State,
+    style: &'a <Theme as StyleSheet>::Style,
+    easing: &'a Easing,
+    bar_height: f32,
+}
+
+impl<'a, Message, Theme>
+    canvas::Program<Message, iced_widget::renderer::Renderer<Theme>>
+    for StateWithStyle<'a, Theme>
+where
+    Theme: StyleSheet,
+{
+    type State = ();
+
+    fn update(
+        &self,
+        _state: &mut Self::State,
+        _event: canvas::Event,
+        _bounds: Rectangle,
+        _cursor: canvas::Cursor,
+    ) -> (canvas::event::Status, Option<Message>) {
+        (canvas::event::Status::Ignored, None)
+    }
+
+    fn draw(
+        &self,
+        _state: &Self::State,
+        renderer: &iced_widget::renderer::Renderer<Theme>,
+        theme: &Theme,
+        bounds: Rectangle,
+        _cursor: canvas::Cursor,
+    ) -> Vec<canvas::Geometry> {
+        let mut frame = canvas::Frame::new(renderer, bounds.size());
+        let custom_style = <Theme as StyleSheet>::appearance(theme, self.style);
+        let track_radius = frame.width() / 2.0 - self.bar_height;
+
+        if let Some(Background::Color(color)) = custom_style.background {
+            let background_path =
+                canvas::Path::circle(frame.center(), track_radius);
+            frame.fill(&background_path, color);
+        }
+
+        let track_path = canvas::Path::circle(frame.center(), track_radius);
+
+        frame.stroke(
+            &track_path,
+            canvas::Stroke::default()
+                .with_color(custom_style.track_color)
+                .with_width(self.bar_height),
+        );
+
+        let mut builder = canvas::path::Builder::new();
+
+        let start = self.state.procession() * 2.0 * PI;
+
+        match self.state {
+            State::Expanding { progress, .. } => {
+                builder.arc(canvas::path::Arc {
+                    center: frame.center(),
+                    radius: track_radius,
+                    start_angle: start,
+                    end_angle: start
+                        + MIN_RADIANS
+                        + WRAP_RADIANS * (self.easing.y_at_x(*progress)),
+                });
+            }
+            State::Contracting { progress, .. } => {
+                builder.arc(canvas::path::Arc {
+                    center: frame.center(),
+                    radius: track_radius,
+                    start_angle: start
+                        + WRAP_RADIANS * (self.easing.y_at_x(*progress)),
+                    end_angle: start + MIN_RADIANS + WRAP_RADIANS,
+                });
+            }
+        }
+
+        let bar_path = builder.build();
+
+        frame.stroke(
+            &bar_path,
+            canvas::Stroke::default()
+                .with_color(custom_style.bar_color)
+                .with_width(self.bar_height),
+        );
+
+        vec![frame.into_geometry()]
+    }
+}

examples/loading_spinners/src/easing.rs

@@ -0,0 +1,132 @@
+use iced_core::Point;
+use lyon::algorithms::measure::PathMeasurements;
+use lyon::path::builder::NoAttributes;
+use lyon::path::path::BuilderImpl;
+use lyon::path::Path;
+
+use once_cell::sync::Lazy;
+
+pub static EMPHASIZED: Lazy<Easing> = Lazy::new(|| {
+    Easing::builder()
+        .cubic_bezier_to([0.05, 0.0], [0.133333, 0.06], [0.166666, 0.4])
+        .cubic_bezier_to([0.208333, 0.82], [0.25, 1.0], [1.0, 1.0])
+        .build()
+});
+
+pub static EMPHASIZED_DECELERATE: Lazy<Easing> = Lazy::new(|| {
+    Easing::builder()
+        .cubic_bezier_to([0.05, 0.7], [0.1, 1.0], [1.0, 1.0])
+        .build()
+});
+
+pub static EMPHASIZED_ACCELERATE: Lazy<Easing> = Lazy::new(|| {
+    Easing::builder()
+        .cubic_bezier_to([0.3, 0.0], [0.8, 0.15], [1.0, 1.0])
+        .build()
+});
+
+pub static STANDARD: Lazy<Easing> = Lazy::new(|| {
+    Easing::builder()
+        .cubic_bezier_to([0.2, 0.0], [0.0, 1.0], [1.0, 1.0])
+        .build()
+});
+
+pub static STANDARD_DECELERATE: Lazy<Easing> = Lazy::new(|| {
+    Easing::builder()
+        .cubic_bezier_to([0.0, 0.0], [0.0, 1.0], [1.0, 1.0])
+        .build()
+});
+
+pub static STANDARD_ACCELERATE: Lazy<Easing> = Lazy::new(|| {
+    Easing::builder()
+        .cubic_bezier_to([0.3, 0.0], [1.0, 1.0], [1.0, 1.0])
+        .build()
+});
+
+pub struct Easing {
+    path: Path,
+    measurements: PathMeasurements,
+}
+
+impl Easing {
+    pub fn builder() -> Builder {
+        Builder::new()
+    }
+
+    pub fn y_at_x(&self, x: f32) -> f32 {
+        let mut sampler = self.measurements.create_sampler(
+            &self.path,
+            lyon::algorithms::measure::SampleType::Normalized,
+        );
+        let sample = sampler.sample(x);
+
+        sample.position().y
+    }
+}
+
+pub struct Builder(NoAttributes<BuilderImpl>);
+
+impl Builder {
+    pub fn new() -> Self {
+        let mut builder = Path::builder();
+        builder.begin(lyon::geom::point(0.0, 0.0));
+
+        Self(builder)
+    }
+
+    /// Adds a line segment. Points must be between 0,0 and 1,1
+    pub fn line_to(mut self, to: impl Into<Point>) -> Self {
+        self.0.line_to(Self::point(to));
+
+        self
+    }
+
+    /// Adds a quadratic bézier curve. Points must be between 0,0 and 1,1
+    pub fn quadratic_bezier_to(
+        mut self,
+        ctrl: impl Into<Point>,
+        to: impl Into<Point>,
+    ) -> Self {
+        self.0
+            .quadratic_bezier_to(Self::point(ctrl), Self::point(to));
+
+        self
+    }
+
+    /// Adds a cubic bézier curve. Points must be between 0,0 and 1,1
+    pub fn cubic_bezier_to(
+        mut self,
+        ctrl1: impl Into<Point>,
+        ctrl2: impl Into<Point>,
+        to: impl Into<Point>,
+    ) -> Self {
+        self.0.cubic_bezier_to(
+            Self::point(ctrl1),
+            Self::point(ctrl2),
+            Self::point(to),
+        );
+
+        self
+    }
+
+    pub fn build(mut self) -> Easing {
+        self.0.line_to(lyon::geom::point(1.0, 1.0));
+        self.0.end(false);
+
+        let path = self.0.build();
+        let measurements = PathMeasurements::from_path(&path, 0.0);
+
+        Easing { path, measurements }
+    }
+
+    fn point(p: impl Into<Point>) -> lyon::geom::Point<f32> {
+        let p: Point = p.into();
+        lyon::geom::point(p.x.min(1.0).max(0.0), p.y.min(1.0).max(0.0))
+    }
+}
+
+impl Default for Builder {
+    fn default() -> Self {
+        Self::new()
+    }
+}

examples/loading_spinners/src/linear.rs

@@ -0,0 +1,324 @@
+//! Show a linear progress indicator.
+use iced::window;
+use iced_core::event::{self, Event};
+use iced_core::renderer;
+use iced_core::time::Instant;
+use iced_core::widget::tree::{self, Tree};
+use iced_core::window::RedrawRequest;
+use iced_core::{layout, Size};
+use iced_core::{
+    Background, Clipboard, Color, Element, Layout, Length, Point, Rectangle,
+    Shell, Widget,
+};
+
+use super::easing::{self, Easing};
+
+use std::time::Duration;
+
+#[allow(missing_debug_implementations)]
+pub struct Linear<'a, Renderer>
+where
+    Renderer: iced_core::Renderer,
+    Renderer::Theme: StyleSheet,
+{
+    width: Length,
+    height: Length,
+    style: <Renderer::Theme as StyleSheet>::Style,
+    easing: &'a Easing,
+    cycle_duration: Duration,
+}
+
+impl<'a, Renderer> Linear<'a, Renderer>
+where
+    Renderer: iced_widget::core::Renderer,
+    Renderer::Theme: StyleSheet,
+{
+    /// Creates a new [`Linear`] with the given content.
+    pub fn new() -> Self {
+        Linear {
+            width: Length::Fixed(100.0),
+            height: Length::Fixed(4.0),
+            style: <Renderer::Theme as StyleSheet>::Style::default(),
+            easing: &easing::STANDARD,
+            cycle_duration: Duration::from_millis(600),
+        }
+    }
+
+    /// Sets the width of the [`Linear`].
+    pub fn width(mut self, width: impl Into<Length>) -> Self {
+        self.width = width.into();
+        self
+    }
+
+    /// Sets the height of the [`Linear`].
+    pub fn height(mut self, height: impl Into<Length>) -> Self {
+        self.height = height.into();
+        self
+    }
+
+    /// Sets the style variant of this [`Linear`].
+    pub fn style(
+        mut self,
+        style: <Renderer::Theme as StyleSheet>::Style,
+    ) -> Self {
+        self.style = style;
+        self
+    }
+
+    /// Sets the motion easing of this [`Linear`].
+    pub fn easing(mut self, easing: &'a Easing) -> Self {
+        self.easing = easing;
+        self
+    }
+
+    /// Sets the cycle duration of this [`Linear`].
+    pub fn cycle_duration(mut self, duration: Duration) -> Self {
+        self.cycle_duration = duration / 2;
+        self
+    }
+}
+
+impl<'a, Renderer> Default for Linear<'a, Renderer>
+where
+    Renderer: iced_core::Renderer,
+    Renderer::Theme: StyleSheet,
+{
+    fn default() -> Self {
+        Self::new()
+    }
+}
+
+#[derive(Clone, Copy)]
+enum State {
+    Expanding { start: Instant, progress: f32 },
+    Contracting { start: Instant, progress: f32 },
+}
+
+impl Default for State {
+    fn default() -> Self {
+        Self::Expanding {
+            start: Instant::now(),
+            progress: 0.0,
+        }
+    }
+}
+
+impl State {
+    fn next(&self, now: Instant) -> Self {
+        match self {
+            Self::Expanding { .. } => Self::Contracting {
+                start: now,
+                progress: 0.0,
+            },
+            Self::Contracting { .. } => Self::Expanding {
+                start: now,
+                progress: 0.0,
+            },
+        }
+    }
+
+    fn start(&self) -> Instant {
+        match self {
+            Self::Expanding { start, .. } | Self::Contracting { start, .. } => {
+                *start
+            }
+        }
+    }
+
+    fn timed_transition(&self, cycle_duration: Duration, now: Instant) -> Self {
+        let elapsed = now.duration_since(self.start());
+
+        match elapsed {
+            elapsed if elapsed > cycle_duration => self.next(now),
+            _ => self.with_elapsed(cycle_duration, elapsed),
+        }
+    }
+
+    fn with_elapsed(
+        &self,
+        cycle_duration: Duration,
+        elapsed: Duration,
+    ) -> Self {
+        let progress = elapsed.as_secs_f32() / cycle_duration.as_secs_f32();
+        match self {
+            Self::Expanding { start, .. } => Self::Expanding {
+                start: *start,
+                progress,
+            },
+            Self::Contracting { start, .. } => Self::Contracting {
+                start: *start,
+                progress,
+            },
+        }
+    }
+}
+
+impl<'a, Message, Renderer> Widget<Message, Renderer> for Linear<'a, Renderer>
+where
+    Message: 'a + Clone,
+    Renderer: 'a + iced_core::Renderer,
+    Renderer::Theme: StyleSheet,
+{
+    fn tag(&self) -> tree::Tag {
+        tree::Tag::of::<State>()
+    }
+
+    fn state(&self) -> tree::State {
+        tree::State::new(State::default())
+    }
+
+    fn width(&self) -> Length {
+        self.width
+    }
+
+    fn height(&self) -> Length {
+        self.height
+    }
+
+    fn layout(
+        &self,
+        _renderer: &Renderer,
+        limits: &layout::Limits,
+    ) -> layout::Node {
+        let limits = limits.width(self.width).height(self.height);
+        let size = limits.resolve(Size::ZERO);
+
+        layout::Node::new(size)
+    }
+
+    fn on_event(
+        &mut self,
+        tree: &mut Tree,
+        event: Event,
+        _layout: Layout<'_>,
+        _cursor_position: Point,
+        _renderer: &Renderer,
+        _clipboard: &mut dyn Clipboard,
+        shell: &mut Shell<'_, Message>,
+    ) -> event::Status {
+        let state = tree.state.downcast_mut::<State>();
+
+        if let Event::Window(window::Event::RedrawRequested(now)) = event {
+            *state = state.timed_transition(self.cycle_duration, now);
+
+            shell.request_redraw(RedrawRequest::NextFrame);
+        }
+
+        event::Status::Ignored
+    }
+
+    fn draw(
+        &self,
+        tree: &Tree,
+        renderer: &mut Renderer,
+        theme: &Renderer::Theme,
+        _style: &renderer::Style,
+        layout: Layout<'_>,
+        _cursor_position: Point,
+        _viewport: &Rectangle,
+    ) {
+        let bounds = layout.bounds();
+        let custom_style = theme.appearance(&self.style);
+        let state = tree.state.downcast_ref::<State>();
+
+        renderer.fill_quad(
+            renderer::Quad {
+                bounds: Rectangle {
+                    x: bounds.x,
+                    y: bounds.y,
+                    width: bounds.width,
+                    height: bounds.height,
+                },
+                border_radius: 0.0.into(),
+                border_width: 0.0,
+                border_color: Color::TRANSPARENT,
+            },
+            Background::Color(custom_style.track_color),
+        );
+
+        match state {
+            State::Expanding { progress, .. } => renderer.fill_quad(
+                renderer::Quad {
+                    bounds: Rectangle {
+                        x: bounds.x,
+                        y: bounds.y,
+                        width: self.easing.y_at_x(*progress) * bounds.width,
+                        height: bounds.height,
+                    },
+                    border_radius: 0.0.into(),
+                    border_width: 0.0,
+                    border_color: Color::TRANSPARENT,
+                },
+                Background::Color(custom_style.bar_color),
+            ),
+
+            State::Contracting { progress, .. } => renderer.fill_quad(
+                renderer::Quad {
+                    bounds: Rectangle {
+                        x: bounds.x
+                            + self.easing.y_at_x(*progress) * bounds.width,
+                        y: bounds.y,
+                        width: (1.0 - self.easing.y_at_x(*progress))
+                            * bounds.width,
+                        height: bounds.height,
+                    },
+                    border_radius: 0.0.into(),
+                    border_width: 0.0,
+                    border_color: Color::TRANSPARENT,
+                },
+                Background::Color(custom_style.bar_color),
+            ),
+        }
+    }
+}
+
+impl<'a, Message, Renderer> From<Linear<'a, Renderer>>
+    for Element<'a, Message, Renderer>
+where
+    Message: Clone + 'a,
+    Renderer: iced_core::Renderer + 'a,
+    Renderer::Theme: StyleSheet,
+{
+    fn from(linear: Linear<'a, Renderer>) -> Self {
+        Self::new(linear)
+    }
+}
+
+#[derive(Debug, Clone, Copy)]
+pub struct Appearance {
+    /// The track [`Color`] of the progress indicator.
+    pub track_color: Color,
+    /// The bar [`Color`] of the progress indicator.
+    pub bar_color: Color,
+}
+
+impl std::default::Default for Appearance {
+    fn default() -> Self {
+        Self {
+            track_color: Color::TRANSPARENT,
+            bar_color: Color::BLACK,
+        }
+    }
+}
+
+/// A set of rules that dictate the style of an indicator.
+pub trait StyleSheet {
+    /// The supported style of the [`StyleSheet`].
+    type Style: Default;
+
+    /// Produces the active [`Appearance`] of a indicator.
+    fn appearance(&self, style: &Self::Style) -> Appearance;
+}
+
+impl StyleSheet for iced::Theme {
+    type Style = ();
+
+    fn appearance(&self, _style: &Self::Style) -> Appearance {
+        let palette = self.extended_palette();
+
+        Appearance {
+            track_color: palette.background.weak.color,
+            bar_color: palette.primary.base.color,
+        }
+    }
+}

examples/loading_spinners/src/main.rs

@@ -0,0 +1,118 @@
+use iced::executor;
+use iced::widget::{column, container, row, slider, text};
+use iced::{Application, Command, Element, Length, Settings, Theme};
+
+use std::time::Duration;
+
+mod circular;
+mod easing;
+mod linear;
+
+use circular::Circular;
+use linear::Linear;
+
+pub fn main() -> iced::Result {
+    LoadingSpinners::run(Settings {
+        antialiasing: true,
+        ..Default::default()
+    })
+}
+
+struct LoadingSpinners {
+    cycle_duration: f32,
+}
+
+impl Default for LoadingSpinners {
+    fn default() -> Self {
+        Self {
+            cycle_duration: 2.0,
+        }
+    }
+}
+
+#[derive(Debug, Clone, Copy)]
+enum Message {
+    CycleDurationChanged(f32),
+}
+
+impl Application for LoadingSpinners {
+    type Message = Message;
+    type Flags = ();
+    type Executor = executor::Default;
+    type Theme = Theme;
+
+    fn new(_flags: Self::Flags) -> (Self, Command<Message>) {
+        (Self::default(), Command::none())
+    }
+
+    fn title(&self) -> String {
+        String::from("Loading Spinners - Iced")
+    }
+
+    fn update(&mut self, message: Message) -> Command<Message> {
+        match message {
+            Message::CycleDurationChanged(duration) => {
+                self.cycle_duration = duration;
+            }
+        }
+
+        Command::none()
+    }
+
+    fn view(&self) -> Element<Message> {
+        let column = [
+            &easing::EMPHASIZED,
+            &easing::EMPHASIZED_DECELERATE,
+            &easing::EMPHASIZED_ACCELERATE,
+            &easing::STANDARD,
+            &easing::STANDARD_DECELERATE,
+            &easing::STANDARD_ACCELERATE,
+        ]
+        .iter()
+        .zip([
+            "Emphasized:",
+            "Emphasized Decelerate:",
+            "Emphasized Accelerate:",
+            "Standard:",
+            "Standard Decelerate:",
+            "Standard Accelerate:",
+        ])
+        .fold(column![], |column, (easing, label)| {
+            column.push(
+                row![
+                    text(label).width(250),
+                    Linear::new().easing(easing).cycle_duration(
+                        Duration::from_secs_f32(self.cycle_duration)
+                    ),
+                    Circular::new().easing(easing).cycle_duration(
+                        Duration::from_secs_f32(self.cycle_duration)
+                    )
+                ]
+                .align_items(iced::Alignment::Center)
+                .spacing(20.0),
+            )
+        })
+        .spacing(20);
+
+        container(
+            column.push(
+                row(vec![
+                    text("Cycle duration:").into(),
+                    slider(1.0..=1000.0, self.cycle_duration * 100.0, |x| {
+                        Message::CycleDurationChanged(x / 100.0)
+                    })
+                    .width(200.0)
+                    .into(),
+                    text(format!("{:.2}s", self.cycle_duration)).into(),
+                ])
+                .align_items(iced::Alignment::Center)
+                .spacing(20.0),
+            ),
+        )
+        .width(Length::Fill)
+        .height(Length::Fill)
+        .center_x()
+        .center_y()
+        .into()
+    }
+}