Optimize cubic Bezier sampling a bit
@@ -1736,12 +1736,15 @@ impl CubicAxis {
}
impl SolveT for CubicAxis {
fn sample(&self, t: f32) -> f32 {
- // FIXME(pcwalton): Use Horner's method or something.
- let p01 = lerp(self.from, self.ctrl0, t);
- let p12 = lerp(self.ctrl0, self.ctrl1, t);
- let p23 = lerp(self.ctrl1, self.to, t);
- let (p012, p123) = (lerp(p01, p12, t), lerp(p12, p23, t));
- lerp(p012, p123, t)
+ let t2 = t * t;
+ let t3 = t2 * t;
+
+ let c3 = self.to + 3.0 * (self.ctrl0 - self.ctrl1) - self.from;
+ let c2 = 3.0 * (self.from - 2.0 * self.ctrl0 + self.ctrl1);
+ let c1 = 3.0 * (self.ctrl0 - self.from);
+ let c0 = self.from;
+
+ c3 * t3 + c2 * t2 + c1 * t + c0
}
fn sample_deriv(&self, t: f32) -> f32 {
let inv_t = 1.0 - t;
