2 files changed, 51 insertions, 0 deletions
diff --git a/src/animation/mod.rs b/src/animation/mod.rs
index 073b0ae3..a68b3342 100644
--- a/src/animation/mod.rs
+++ b/src/animation/mod.rs
@@ -16,6 +16,8 @@ pub struct Animation {
     from: f64,
     to: f64,
     duration: Duration,
+    /// Time until the animation first reaches `to`.
+    clamped_duration: Duration,
     start_time: Duration,
     current_time: Duration,
     kind: Kind,
@@ -106,6 +108,8 @@ impl Animation {
             from,
             to,
             duration,
+            // Our current curves never overshoot.
+            clamped_duration: duration,
             start_time: now,
             current_time: now,
             kind,
@@ -118,12 +122,14 @@ impl Animation {
         let now = get_monotonic_time();
 
         let duration = spring.duration();
+        let clamped_duration = spring.clamped_duration();
         let kind = Kind::Spring(spring);
 
         Self {
             from: spring.from,
             to: spring.to,
             duration,
+            clamped_duration,
             start_time: now,
             current_time: now,
             kind,
@@ -159,6 +165,7 @@ impl Animation {
             from,
             to,
             duration,
+            clamped_duration: duration,
             start_time: now,
             current_time: now,
             kind,
@@ -228,6 +235,10 @@ impl Animation {
         self.current_time >= self.start_time + self.duration
     }
 
+    pub fn is_clamped_done(&self) -> bool {
+        self.current_time >= self.start_time + self.clamped_duration
+    }
+
     pub fn value(&self) -> f64 {
         if self.is_done() {
             return self.to;
@@ -254,6 +265,15 @@ impl Animation {
         }
     }
 
+    /// Returns a value that stops at the target value after first reaching it.
+    pub fn clamped_value(&self) -> f64 {
+        if self.is_clamped_done() {
+            return self.to;
+        }
+
+        self.value()
+    }
+
     pub fn to(&self) -> f64 {
         self.to
     }
diff --git a/src/animation/spring.rs b/src/animation/spring.rs
index 6e100f05..506b01a3 100644
--- a/src/animation/spring.rs
+++ b/src/animation/spring.rs
@@ -96,6 +96,37 @@ impl Spring {
         Duration::from_secs_f64(x1)
     }
 
+    /// Computes and returns the duration until the spring reaches its target position.
+    pub fn clamped_duration(&self) -> Duration {
+        let beta = self.params.damping / (2. * self.params.mass);
+
+        if beta.abs() <= f64::EPSILON || beta < 0. {
+            return Duration::MAX;
+        }
+
+        if (self.to - self.from).abs() <= f64::EPSILON {
+            return Duration::ZERO;
+        }
+
+        // The first frame is not that important and we avoid finding the trivial 0 for in-place
+        // animations.
+        let mut i = 1u16;
+        let mut y = self.oscillate(f64::from(i) / 1000.);
+
+        while (self.to - self.from > f64::EPSILON && self.to - y > self.params.epsilon)
+            || (self.from - self.to > f64::EPSILON && y - self.to > self.params.epsilon)
+        {
+            if i > 1000 {
+                return Duration::ZERO;
+            }
+
+            i += 1;
+            y = self.oscillate(f64::from(i) / 1000.);
+        }
+
+        Duration::from_millis(u64::from(i))
+    }
+
     /// Returns the spring position at a given time in seconds.
     fn oscillate(&self, t: f64) -> f64 {
         let b = self.params.damping;