Add MathUtils.damp()

docs/api/en/math/MathUtils.html

@@ -71,6 +71,17 @@
 
 		Returns a value that alternates between 0 and [param:Float length].</p>
 
+		<h3>[method:Float damp]( [param:Float x], [param:Float y], [param:Float lambda], [param:Float dt] )</h3>
+		<p>
+		[page:Float x] - Current point. <br />
+		[page:Float y] - Target point. <br />
+		[page:Float lambda] - A higher lambda value will make the movement more sudden, and a lower value will make the movement more gradual. <br />
+		[page:Float dt] - Delta time in seconds.<br><br />
+
+		Smoothly interpolate a number from [page:Float x] toward [page:Float y] in a spring-like manner using the [page:Float dt] to maintain frame rate independent movement.
+		For details, see [link:http://www.rorydriscoll.com/2016/03/07/frame-rate-independent-damping-using-lerp/ Frame Rate Independent Damping Using Lerp].
+		</p>
+
 		<h3>[method:Integer ceilPowerOfTwo]( [param:Number n] )</h3>
 		<p>Returns the smallest power of 2 that is greater than or equal to [page:Number n].</p>
 

docs/api/zh/math/MathUtils.html

@@ -68,6 +68,17 @@
 
 		Returns a value that alternates between 0 and [param:Float length].</p>
 
+		<h3>[method:Float damp]( [param:Float x], [param:Float y], [param:Float lambda], [param:Float dt] )</h3>
+		<p>
+		[page:Float x] - Current point. <br />
+		[page:Float y] - Target point. <br />
+		[page:Float lambda] - A higher lambda value will make the movement more sudden, and a lower value will make the movement more gradual. <br />
+		[page:Float dt] - Delta time in seconds.<br><br />
+
+		Smoothly interpolate a number from [page:Float x] toward [page:Float y] in a spring-like manner using the [page:Float dt] to maintain frame rate independent movement.
+		For details, see [link:http://www.rorydriscoll.com/2016/03/07/frame-rate-independent-damping-using-lerp/ Frame Rate Independent Damping Using Lerp].
+		</p>
+
 		<h3>[method:Integer ceilPowerOfTwo]( [param:Number n] )</h3>
 		<p>返回大于等于 [page:Number n] 的2的最小次幂。</p>
 

src/math/MathUtils.d.ts

@@ -94,6 +94,18 @@ export namespace MathUtils {
 	 */
 	export function pingpong( x: number, length?: number ): number;
 
+	/**
+	 * Smoothly interpolate a number from x toward y in a spring-like
+	 * manner using the dt to maintain frame rate independent movement.
+	 *
+	 * @param x Current point.
+	 * @param y Target point.
+	 * @param lambda A higher lambda value will make the movement more sudden, and a lower value will make the movement more gradual.
+	 * @param dt Delta time in seconds.
+	 * @return {number}
+	 */
+	export function damp( x: number, y: number, lambda: number, dt: number ): number;
+
 	/**
 	 * @deprecated Use {@link Math#floorPowerOfTwo .floorPowerOfTwo()}
 	 */

src/math/MathUtils.js

@@ -70,6 +70,14 @@ const MathUtils = {
 
 	},
 
+	// http://www.rorydriscoll.com/2016/03/07/frame-rate-independent-damping-using-lerp/
+
+	damp: function ( x, y, lambda, dt ) {
+
+		return MathUtils.lerp( x, y, 1 - Math.exp( - lambda * dt ) );
+
+	},
+
 	// http://en.wikipedia.org/wiki/Smoothstep
 
 	smoothstep: function ( x, min, max ) {