From ea29e088369ffba3f04934ebae81eeb14d9af01f Mon Sep 17 00:00:00 2001
From: Dimitri Sabadie <dimitri.sabadie@gmail.com>
Date: Tue, 24 Sep 2019 21:31:18 +0200
Subject: [PATCH] =?UTF-8?q?Fix=20cubic=20B=C3=A9zier=20interpolation.?=
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---
 CHANGELOG.md       | 9 ++++++++-
 Cargo.toml         | 2 +-
 src/interpolate.rs | 5 ++++-
 3 files changed, 13 insertions(+), 3 deletions(-)

diff --git a/CHANGELOG.md b/CHANGELOG.md
index 3e986d3..e48e0ed 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -1,6 +1,13 @@
+# 2.0.1
+
+> Tue Sep 24th 2019
+
+- Fix the cubic Bézier curve interpolation. The “output” tangent is now taken by mirroring the
+  next key’s tangent around its control point.
+
 # 2.0.0
 
-> Mon Sep 24th 2019
+> Mon Sep 23rd 2019
 
 ## Major changes
 
diff --git a/Cargo.toml b/Cargo.toml
index 413e427..cd82274 100644
--- a/Cargo.toml
+++ b/Cargo.toml
@@ -1,6 +1,6 @@
 [package]
 name = "splines"
-version = "2.0.0"
+version = "2.0.1"
 license = "BSD-3-Clause"
 authors = ["Dimitri Sabadie <dimitri.sabadie@gmail.com>"]
 description = "Spline interpolation made easy"
diff --git a/src/interpolate.rs b/src/interpolate.rs
index 36042e2..2f1b3c2 100644
--- a/src/interpolate.rs
+++ b/src/interpolate.rs
@@ -240,7 +240,10 @@ where V: Linear<T>,
   let one_t_3 = one_t_2 * one_t;
   let three = T::one() + T::one() + T::one();
 
-  a.outer_mul(one_t_3) + u.outer_mul(three * one_t_2 * t) + v.outer_mul(three * one_t * t * t) + b.outer_mul(t * t * t)
+  // mirror the “output” tangent based on the next key “input” tangent
+  let v_ = b + b - v;
+
+  a.outer_mul(one_t_3) + u.outer_mul(three * one_t_2 * t) + v_.outer_mul(three * one_t * t * t) + b.outer_mul(t * t * t)
 }
 
 macro_rules! impl_interpolate_simple {