also for DQuat

src/glam.rs

@@ -94,8 +94,24 @@ impl Interpolate<f64> for DQuat {
   }
 
   fn cubic_hermite(t: f64, x: (f64, Self), a: (f64, Self), b: (f64, Self), y: (f64, Self)) -> Self {
-      unimplemented!("Need to figure this out for quaternions")
-    }
+      // sampler stuff
+      let two_t = t * 2.;
+      let three_t = t * 3.;
+      let t2 = t * t;
+      let t3 = t2 * t;
+      let two_t3 = t2 * two_t;
+      let two_t2 = t * two_t;
+      let three_t2 = t * three_t;
+
+      // tangents
+      let m0 = (b.1 - x.1) / (b.0 - x.0) * (b.0 - a.0);
+      let m1 = (y.1 - a.1) / (y.0 - a.0) * (b.0 - a.0);
+
+      a.1 * (two_t3 - three_t2 + 1.)
+        + m0 * (t3 - two_t2 + t)
+        + b.1 * (three_t2 - two_t3)
+        + m1 * (t3 - t2)
+  }
 
   fn quadratic_bezier(t: f64, a: Self, u: Self, b: Self) -> Self {
     // ⚠️ UNTESTED ⚠️