animation/spring: Add a check for from = to in duration()

The overdamped code below was dividing by zero in this case and triggering a
panic.

1 files changed, 22 insertions, 0 deletions

diff --git a/src/animation/spring.rs b/src/animation/spring.rs
index 226d7cc2..f7bcb1e4 100644
--- a/src/animation/spring.rs
+++ b/src/animation/spring.rs
@@ -54,6 +54,10 @@ impl Spring {
             return Duration::MAX;
         }
 
+        if (self.to - self.from).abs() <= f64::EPSILON {
+            return Duration::ZERO;
+        }
+
         let omega0 = (self.params.stiffness / self.params.mass).sqrt();
 
         // As first ansatz for the overdamped solution,
@@ -166,3 +170,21 @@ impl Spring {
         }
     }
 }
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    #[test]
+    fn overdamped_spring_equal_from_to_nan() {
+        let spring = Spring {
+            from: 0.,
+            to: 0.,
+            initial_velocity: 0.,
+            params: SpringParams::new(1.15, 850., 0.0001),
+        };
+        let _ = spring.duration();
+        let _ = spring.clamped_duration();
+        let _ = spring.value_at(Duration::ZERO);
+    }
+}