Enable non-linear easing (#32)

Fix for #31 based on linebender/velato#42. 

One difference is that I had to enable `mint_types` feature for
`keyframe` crate dependency that pulls in `mint`. As far as I can tell
the project is still `#![no_std]`.

.typos.toml

@@ -8,7 +8,7 @@
 
 # Match Identifier - Case Sensitive
 [default.extend-identifiers]
-t1_iy = "t1_iy"
+t0_iy = "t0_iy"
 
 # Match Inside a Word - Case Insensitive
 [default.extend-words]

Cargo.toml

@@ -27,7 +27,7 @@ vello = ["dep:vello"]
 
 [dependencies]
 hashbrown = "0.15.0"
-keyframe = { version = "1.1.1", default-features = false }
+keyframe = { version = "1.1.1", default-features = false, features = ["mint_types"] }
 kurbo = { version = "0.11", default-features = false }
 peniko = { version = "0.1.1", default-features = false }
 vello = { version = "0.2.0", default-features = false, optional = true }

src/value.rs

@@ -120,10 +120,10 @@ impl Time {
         let t0 = times[ix0];
         let t1 = times[ix1];
         let (t0_ox, t0_oy) = t0.out_tangent.map(|o| (o.x, o.y)).unwrap_or((0.0, 0.0));
-        let (t1_ix, t1_iy) = t1.in_tangent.map(|i| (i.x, i.y)).unwrap_or((1.0, 1.0));
+        let (t0_ix, t0_iy) = t0.in_tangent.map(|i| (i.x, i.y)).unwrap_or((1.0, 1.0));
         let easing = Easing {
             o: EasingHandle { x: t0_ox, y: t0_oy },
-            i: EasingHandle { x: t1_ix, y: t1_iy },
+            i: EasingHandle { x: t0_ix, y: t0_iy },
         };
         let hold = t0.hold;
         let t = (frame - t0.frame) / (t1.frame - t0.frame);
@@ -161,20 +161,16 @@ pub trait Tween: Clone + Default {
 }
 
 impl Tween for f64 {
-    fn tween(&self, other: &Self, t: f64, _easing: &Easing) -> Self {
-        // TODO: We are enforcing linear interpolation for now, but a decent amount of work is done for easings.
-        keyframe::ease(keyframe::functions::Linear, *self, *other, t)
-
-        // FIXME: Hopefully we can finish this up one day!
-        //keyframe::ease(
-        //    keyframe::functions::BezierCurve::from(
-        //        keyframe::mint::Vector2::from_slice(&[easing.o.x, easing.o.y]),
-        //        keyframe::mint::Vector2::from_slice(&[easing.i.x, easing.i.y]),
-        //    ),
-        //    *self,
-        //    *other,
-        //    t,
-        //)
+    fn tween(&self, other: &Self, t: f64, easing: &Easing) -> Self {
+        keyframe::ease(
+            keyframe::functions::BezierCurve::from(
+                keyframe::mint::Vector2::from_slice(&[easing.o.x, easing.o.y]),
+                keyframe::mint::Vector2::from_slice(&[easing.i.x, easing.i.y]),
+            ),
+            *self,
+            *other,
+            t,
+        )
     }
 }