feat: cubic-bezier curve for animation (#2059)

* feat: bezier curve for animation

* fixes

---------

Co-authored-by: Ivan Molodetskikh <yalterz@gmail.com>

2 files changed, 68 insertions, 0 deletions

diff --git a/src/animation/bezier.rs b/src/animation/bezier.rs
new file mode 100644
index 00000000..17facfda
--- /dev/null
+++ b/src/animation/bezier.rs
@@ -0,0 +1,60 @@
+use keyframe::EasingFunction;
+
+#[derive(Debug, Clone, Copy)]
+pub struct CubicBezier {
+    x1: f64,
+    y1: f64,
+    x2: f64,
+    y2: f64,
+}
+
+impl CubicBezier {
+    pub fn new(x1: f64, y1: f64, x2: f64, y2: f64) -> Self {
+        Self { x1, y1, x2, y2 }
+    }
+
+    // Based on libadwaita (LGPL-2.1-or-later):
+    // https://gitlab.gnome.org/GNOME/libadwaita/-/blob/1.7.6/src/adw-easing.c?ref_type=tags#L469-531
+
+    fn x_for_t(&self, t: f64) -> f64 {
+        let omt = 1. - t;
+        3. * omt * omt * t * self.x1 + 3. * omt * t * t * self.x2 + t * t * t
+    }
+
+    fn y_for_t(&self, t: f64) -> f64 {
+        let omt = 1. - t;
+        3. * omt * omt * t * self.y1 + 3. * omt * t * t * self.y2 + t * t * t
+    }
+
+    fn t_for_x(&self, x: f64) -> f64 {
+        let mut min_t = 0.;
+        let mut max_t = 1.;
+
+        for _ in 0..=30 {
+            let guess_t = (min_t + max_t) / 2.;
+            let guess_x = self.x_for_t(guess_t);
+
+            if x < guess_x {
+                max_t = guess_t;
+            } else {
+                min_t = guess_t;
+            }
+        }
+
+        (min_t + max_t) / 2.
+    }
+}
+
+impl EasingFunction for CubicBezier {
+    fn y(&self, x: f64) -> f64 {
+        if x <= f64::EPSILON {
+            return 0.;
+        }
+
+        if 1. - f64::EPSILON <= x {
+            return 1.;
+        }
+
+        self.y_for_t(self.t_for_x(x))
+    }
+}
diff --git a/src/animation/mod.rs b/src/animation/mod.rs
index a8de3275..73a79c5e 100644
--- a/src/animation/mod.rs
+++ b/src/animation/mod.rs
@@ -3,6 +3,9 @@ use std::time::Duration;
 use keyframe::functions::{EaseOutCubic, EaseOutQuad};
 use keyframe::EasingFunction;
 
+mod bezier;
+use bezier::CubicBezier;
+
 mod spring;
 pub use spring::{Spring, SpringParams};
 
@@ -43,6 +46,7 @@ pub enum Curve {
     EaseOutQuad,
     EaseOutCubic,
     EaseOutExpo,
+    CubicBezier(CubicBezier),
 }
 
 impl Animation {
@@ -342,6 +346,7 @@ impl Curve {
             Curve::EaseOutQuad => EaseOutQuad.y(x),
             Curve::EaseOutCubic => EaseOutCubic.y(x),
             Curve::EaseOutExpo => 1. - 2f64.powf(-10. * x),
+            Curve::CubicBezier(b) => b.y(x),
         }
     }
 }
@@ -353,6 +358,9 @@ impl From<niri_config::animations::Curve> for Curve {
             niri_config::animations::Curve::EaseOutQuad => Curve::EaseOutQuad,
             niri_config::animations::Curve::EaseOutCubic => Curve::EaseOutCubic,
             niri_config::animations::Curve::EaseOutExpo => Curve::EaseOutExpo,
+            niri_config::animations::Curve::CubicBezier(x1, y1, x2, y2) => {
+                Curve::CubicBezier(CubicBezier::new(x1, y1, x2, y2))
+            }
         }
     }
 }