Draft basic `Animation` API in `iced_core`

6 files changed, 124 insertions, 3 deletions

diff --git a/Cargo.lock b/Cargo.lock
index 9b64572e..aa774409 100644
--- a/Cargo.lock
+++ b/Cargo.lock
@@ -2439,6 +2439,7 @@ dependencies = [
  "bytes",
  "dark-light",
  "glam",
+ "lilt",
  "log",
  "num-traits",
  "palette",
@@ -3065,6 +3066,12 @@ dependencies = [
 ]
 
 [[package]]
+name = "lilt"
+version = "0.7.0"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "a095f60643436f4a6bddb82f7f37c1a9247990a2ee3421cf4faa43715edd5896"
+
+[[package]]
 name = "linked-hash-map"
 version = "0.5.6"
 source = "registry+https://github.com/rust-lang/crates.io-index"
diff --git a/Cargo.toml b/Cargo.toml
index 89c28139..156d673b 100644
--- a/Cargo.toml
+++ b/Cargo.toml
@@ -158,6 +158,7 @@ half = "2.2"
 image = { version = "0.25", default-features = false }
 kamadak-exif = "0.5"
 kurbo = "0.10"
+lilt = "0.7"
 log = "0.4"
 lyon = "1.0"
 lyon_path = "1.0"
diff --git a/core/Cargo.toml b/core/Cargo.toml
index a3bc6745..1ca7260c 100644
--- a/core/Cargo.toml
+++ b/core/Cargo.toml
@@ -21,6 +21,7 @@ advanced = []
 bitflags.workspace = true
 bytes.workspace = true
 glam.workspace = true
+lilt.workspace = true
 log.workspace = true
 num-traits.workspace = true
 palette.workspace = true
diff --git a/core/src/animation.rs b/core/src/animation.rs
new file mode 100644
index 00000000..eae6785e
--- /dev/null
+++ b/core/src/animation.rs
@@ -0,0 +1,109 @@
+//! Animate your applications.
+use crate::time::{Duration, Instant};
+
+pub use lilt::{Easing, FloatRepresentable as Float, Interpolable};
+
+/// The animation of some particular state.
+///
+/// It tracks state changes and allows projecting interpolated values
+/// through time.
+#[derive(Debug, Clone)]
+pub struct Animation<T>
+where
+    T: Clone + Copy + PartialEq + Float,
+{
+    raw: lilt::Animated<T, Instant>,
+}
+
+impl<T> Animation<T>
+where
+    T: Clone + Copy + PartialEq + Float,
+{
+    /// Creates a new [`Animation`] with the given initial state.
+    pub fn new(state: T) -> Self {
+        Self {
+            raw: lilt::Animated::new(state),
+        }
+    }
+
+    /// Sets the [`Easing`] function of the [`Animation`].
+    ///
+    /// See the [Easing Functions Cheat Sheet](https://easings.net) for
+    /// details!
+    pub fn easing(mut self, easing: Easing) -> Self {
+        self.raw = self.raw.easing(easing);
+        self
+    }
+
+    /// Sets the duration of the [`Animation`] to 100ms.
+    pub fn very_quick(self) -> Self {
+        self.duration(Duration::from_millis(100))
+    }
+
+    /// Sets the duration of the [`Animation`] to 200ms.
+    pub fn quick(self) -> Self {
+        self.duration(Duration::from_millis(200))
+    }
+
+    /// Sets the duration of the [`Animation`] to 400ms.
+    pub fn slow(self) -> Self {
+        self.duration(Duration::from_millis(400))
+    }
+
+    /// Sets the duration of the [`Animation`] to 500ms.
+    pub fn very_slow(self) -> Self {
+        self.duration(Duration::from_millis(500))
+    }
+
+    /// Sets the duration of the [`Animation`] to the given value.
+    pub fn duration(mut self, duration: Duration) -> Self {
+        self.raw = self.raw.duration(duration.as_secs_f32() * 1_000.0);
+        self
+    }
+
+    /// Sets a delay for the [`Animation`].
+    pub fn delay(mut self, duration: Duration) -> Self {
+        self.raw = self.raw.delay(duration.as_secs_f64() as f32 * 1000.0);
+        self
+    }
+
+    /// Transitions the [`Animation`] from its current state to the given new state.
+    pub fn go(mut self, new_state: T) -> Self {
+        self.go_mut(new_state);
+        self
+    }
+
+    /// Transitions the [`Animation`] from its current state to the given new state, by reference.
+    pub fn go_mut(&mut self, new_state: T) {
+        self.raw.transition(new_state, Instant::now());
+    }
+
+    /// Returns true if the [`Animation`] is currently in progress.
+    ///
+    /// An [`Animation`] is in progress when it is transitioning to a different state.
+    pub fn in_progress(&self, at: Instant) -> bool {
+        self.raw.in_progress(at)
+    }
+
+    /// Projects the [`Animation`] into an interpolated value at the given [`Instant`]; using the
+    /// closure provided to calculate the different keyframes of interpolated values.
+    ///
+    /// If the [`Animation`] state is a `bool`, you can use the simpler [`interpolate`] method.
+    pub fn interpolate_with<I>(&self, f: impl Fn(T) -> I, at: Instant) -> I
+    where
+        I: Interpolable,
+    {
+        self.raw.animate(f, at)
+    }
+}
+
+impl Animation<bool> {
+    /// Projects the [`Animation`] into an interpolated value at the given [`Instant`]; using the
+    /// `start` and `end` values as the origin and destination keyframes.
+    pub fn interpolate<I>(&self, start: I, end: I, at: Instant) -> I
+    where
+        I: Interpolable + Clone,
+    {
+        self.raw.animate_bool(start, end, at)
+    }
+}
diff --git a/core/src/lib.rs b/core/src/lib.rs
index 645f7a90..16b3aa0f 100644
--- a/core/src/lib.rs
+++ b/core/src/lib.rs
@@ -10,6 +10,7 @@
     html_logo_url = "https://raw.githubusercontent.com/iced-rs/iced/9ab6923e943f784985e9ef9ca28b10278297225d/docs/logo.svg"
 )]
 pub mod alignment;
+pub mod animation;
 pub mod border;
 pub mod clipboard;
 pub mod event;
@@ -49,6 +50,7 @@ mod vector;
 
 pub use alignment::Alignment;
 pub use angle::{Degrees, Radians};
+pub use animation::Animation;
 pub use background::Background;
 pub use border::Border;
 pub use clipboard::Clipboard;
diff --git a/src/lib.rs b/src/lib.rs
index 939943a9..eec844bc 100644
--- a/src/lib.rs
+++ b/src/lib.rs
@@ -498,15 +498,16 @@ pub mod window;
 pub mod advanced;
 
 pub use crate::core::alignment;
+pub use crate::core::animation;
 pub use crate::core::border;
 pub use crate::core::color;
 pub use crate::core::gradient;
 pub use crate::core::padding;
 pub use crate::core::theme;
 pub use crate::core::{
-    Alignment, Background, Border, Color, ContentFit, Degrees, Gradient,
-    Length, Padding, Pixels, Point, Radians, Rectangle, Rotation, Settings,
-    Shadow, Size, Theme, Transformation, Vector,
+    Alignment, Animation, Background, Border, Color, ContentFit, Degrees,
+    Gradient, Length, Padding, Pixels, Point, Radians, Rectangle, Rotation,
+    Settings, Shadow, Size, Theme, Transformation, Vector,
 };
 pub use crate::runtime::exit;
 pub use iced_futures::Subscription;