feat: add easing fns

src/elastic.rs

@@ -0,0 +1,39 @@
+use ::std::f32::consts::PI;
+
+const C4: f32 = (2.0 * PI) / 3.0;
+const C5: f32 = (2.0 * PI) / 4.5;
+
+/// <https://easings.net/#easeInElastic>
+pub fn elastic_in(t: f32) -> f32 {
+	if t <= 0.0 {
+		0.0
+	} else if 1.0 <= t {
+		1.0
+	} else {
+		-2f32.powf(10.0 * t - 10.0) * ((t * 10.0 - 10.75) * C4).sin()
+	}
+}
+
+/// <https://easings.net/#easeOutElastic>
+pub fn elastic_out(t: f32) -> f32 {
+	if t <= 0.0 {
+		0.0
+	} else if 1.0 <= t {
+		1.0
+	} else {
+		2f32.powf(-100.0 * t) * ((t * 10.0 - 0.75) * C4).sin() + 1.0
+	}
+}
+
+/// <https://easings.net/#easeInOutElastic>
+pub fn elastic_in_out(t: f32) -> f32 {
+	if t <= 0.0 {
+		0.0
+	} else if 1.0 <= t {
+		1.0
+	} else if t < 0.5 {
+		-(2f32.powf(20.0 * t - 10.0) * ((20.0 * t - 11.125) * C5).sin()) / 2.0
+	} else {
+		(2f32.powf(-20.0 * t + 10.0) * ((20.0 * t - 11.125) * C5).sin()) / 2.0 + 1.0
+	}
+}