Simple controller for managing squash n stretch on transforms.

Easing.cs

namespace Core.Utils
{

    static public class Easing
    {
        /// <summary>
        /// Constant Pi.
        /// </summary>
        private const float PI = Math.PI;

        /// <summary>
        /// Constant Pi / 2.
        /// </summary>
        private const float HALFPI = Math.PI / 2.0f;

        /// <summary>
        /// Easing Functions enumeration
        /// </summary>
        public enum Functions
        {
            Linear,
            QuadraticEaseIn,
            QuadraticEaseOut,
            QuadraticEaseInOut,
            CubicEaseIn,
            CubicEaseOut,
            CubicEaseInOut,
            QuarticEaseIn,
            QuarticEaseOut,
            QuarticEaseInOut,
            QuinticEaseIn,
            QuinticEaseOut,
            QuinticEaseInOut,
            SineEaseIn,
            SineEaseOut,
            SineEaseInOut,
            CircularEaseIn,
            CircularEaseOut,
            CircularEaseInOut,
            ExponentialEaseIn,
            ExponentialEaseOut,
            ExponentialEaseInOut,
            ElasticEaseIn,
            ElasticEaseOut,
            ElasticEaseInOut,
            BackEaseIn,
            BackEaseOut,
            BackEaseInOut,
            BounceEaseIn,
            BounceEaseOut,
            BounceEaseInOut
        }

        /// <summary>
        /// Interpolate using the specified function.
        /// </summary>
        static public float Interpolate(float p, Functions function)
        {
            switch (function)
            {
                default:
                case Functions.Linear: return Linear(p);
                case Functions.QuadraticEaseOut: return QuadraticEaseOut(p);
                case Functions.QuadraticEaseIn: return QuadraticEaseIn(p);
                case Functions.QuadraticEaseInOut: return QuadraticEaseInOut(p);
                case Functions.CubicEaseIn: return CubicEaseIn(p);
                case Functions.CubicEaseOut: return CubicEaseOut(p);
                case Functions.CubicEaseInOut: return CubicEaseInOut(p);
                case Functions.QuarticEaseIn: return QuarticEaseIn(p);
                case Functions.QuarticEaseOut: return QuarticEaseOut(p);
                case Functions.QuarticEaseInOut: return QuarticEaseInOut(p);
                case Functions.QuinticEaseIn: return QuinticEaseIn(p);
                case Functions.QuinticEaseOut: return QuinticEaseOut(p);
                case Functions.QuinticEaseInOut: return QuinticEaseInOut(p);
                case Functions.SineEaseIn: return SineEaseIn(p);
                case Functions.SineEaseOut: return SineEaseOut(p);
                case Functions.SineEaseInOut: return SineEaseInOut(p);
                case Functions.CircularEaseIn: return CircularEaseIn(p);
                case Functions.CircularEaseOut: return CircularEaseOut(p);
                case Functions.CircularEaseInOut: return CircularEaseInOut(p);
                case Functions.ExponentialEaseIn: return ExponentialEaseIn(p);
                case Functions.ExponentialEaseOut: return ExponentialEaseOut(p);
                case Functions.ExponentialEaseInOut: return ExponentialEaseInOut(p);
                case Functions.ElasticEaseIn: return ElasticEaseIn(p);
                case Functions.ElasticEaseOut: return ElasticEaseOut(p);
                case Functions.ElasticEaseInOut: return ElasticEaseInOut(p);
                case Functions.BackEaseIn: return BackEaseIn(p);
                case Functions.BackEaseOut: return BackEaseOut(p);
                case Functions.BackEaseInOut: return BackEaseInOut(p);
                case Functions.BounceEaseIn: return BounceEaseIn(p);
                case Functions.BounceEaseOut: return BounceEaseOut(p);
                case Functions.BounceEaseInOut: return BounceEaseInOut(p);
            }
        }

        /// <summary>
        /// Modeled after the line y = x
        /// </summary>
        static public float Linear(float p)
        {
            return p;
        }

        /// <summary>
        /// Modeled after the parabola y = x^2
        /// </summary>
        static public float QuadraticEaseIn(float p)
        {
            return p * p;
        }

        /// <summary>
        /// Modeled after the parabola y = -x^2 + 2x
        /// </summary>
        static public float QuadraticEaseOut(float p)
        {
            return -(p * (p - 2));
        }

        /// <summary>
        /// Modeled after the piecewise quadratic
        /// y = (1/2)((2x)^2)             ; [0, 0.5)
        /// y = -(1/2)((2x-1)*(2x-3) - 1) ; [0.5, 1]
        /// </summary>
        static public float QuadraticEaseInOut(float p)
        {
            if (p < 0.5f)
            {
                return 2 * p * p;
            }
            else
            {
                return (-2 * p * p) + (4 * p) - 1;
            }
        }

        /// <summary>
        /// Modeled after the cubic y = x^3
        /// </summary>
        static public float CubicEaseIn(float p)
        {
            return p * p * p;
        }

        /// <summary>
        /// Modeled after the cubic y = (x - 1)^3 + 1
        /// </summary>
        static public float CubicEaseOut(float p)
        {
            float f = (p - 1);
            return f * f * f + 1;
        }

        /// <summary>	
        /// Modeled after the piecewise cubic
        /// y = (1/2)((2x)^3)       ; [0, 0.5)
        /// y = (1/2)((2x-2)^3 + 2) ; [0.5, 1]
        /// </summary>
        static public float CubicEaseInOut(float p)
        {
            if (p < 0.5f)
            {
                return 4 * p * p * p;
            }
            else
            {
                float f = ((2 * p) - 2);
                return 0.5f * f * f * f + 1;
            }
        }

        /// <summary>
        /// Modeled after the quartic x^4
        /// </summary>
        static public float QuarticEaseIn(float p)
        {
            return p * p * p * p;
        }

        /// <summary>
        /// Modeled after the quartic y = 1 - (x - 1)^4
        /// </summary>
        static public float QuarticEaseOut(float p)
        {
            float f = (p - 1);
            return f * f * f * (1 - p) + 1;
        }

        /// <summary>
        // Modeled after the piecewise quartic
        // y = (1/2)((2x)^4)        ; [0, 0.5)
        // y = -(1/2)((2x-2)^4 - 2) ; [0.5, 1]
        /// </summary>
        static public float QuarticEaseInOut(float p)
        {
            if (p < 0.5f)
            {
                return 8 * p * p * p * p;
            }
            else
            {
                float f = (p - 1);
                return -8 * f * f * f * f + 1;
            }
        }

        /// <summary>
        /// Modeled after the quintic y = x^5
        /// </summary>
        static public float QuinticEaseIn(float p)
        {
            return p * p * p * p * p;
        }

        /// <summary>
        /// Modeled after the quintic y = (x - 1)^5 + 1
        /// </summary>
        static public float QuinticEaseOut(float p)
        {
            float f = (p - 1);
            return f * f * f * f * f + 1;
        }

        /// <summary>
        /// Modeled after the piecewise quintic
        /// y = (1/2)((2x)^5)       ; [0, 0.5)
        /// y = (1/2)((2x-2)^5 + 2) ; [0.5, 1]
        /// </summary>
        static public float QuinticEaseInOut(float p)
        {
            if (p < 0.5f)
            {
                return 16 * p * p * p * p * p;
            }
            else
            {
                float f = ((2 * p) - 2);
                return 0.5f * f * f * f * f * f + 1;
            }
        }

        /// <summary>
        /// Modeled after quarter-cycle of sine wave
        /// </summary>
        static public float SineEaseIn(float p)
        {
            return Math.Sin((p - 1) * HALFPI) + 1;
        }

        /// <summary>
        /// Modeled after quarter-cycle of sine wave (different phase)
        /// </summary>
        static public float SineEaseOut(float p)
        {
            return Math.Sin(p * HALFPI);
        }

        /// <summary>
        /// Modeled after half sine wave
        /// </summary>
        static public float SineEaseInOut(float p)
        {
            return 0.5f * (1 - Math.Cos(p * PI));
        }

        /// <summary>
        /// Modeled after shifted quadrant IV of unit circle
        /// </summary>
        static public float CircularEaseIn(float p)
        {
            return 1 - Math.Sqrt(1 - (p * p));
        }

        /// <summary>
        /// Modeled after shifted quadrant II of unit circle
        /// </summary>
        static public float CircularEaseOut(float p)
        {
            return Math.Sqrt((2 - p) * p);
        }

        /// <summary>	
        /// Modeled after the piecewise circular function
        /// y = (1/2)(1 - Math.Sqrt(1 - 4x^2))           ; [0, 0.5)
        /// y = (1/2)(Math.Sqrt(-(2x - 3)*(2x - 1)) + 1) ; [0.5, 1]
        /// </summary>
        static public float CircularEaseInOut(float p)
        {
            if (p < 0.5f)
            {
                return 0.5f * (1 - Math.Sqrt(1 - 4 * (p * p)));
            }
            else
            {
                return 0.5f * (Math.Sqrt(-((2 * p) - 3) * ((2 * p) - 1)) + 1);
            }
        }

        /// <summary>
        /// Modeled after the exponential function y = 2^(10(x - 1))
        /// </summary>
        static public float ExponentialEaseIn(float p)
        {
            return (p == 0.0f) ? p : Math.Pow(2, 10 * (p - 1));
        }

        /// <summary>
        /// Modeled after the exponential function y = -2^(-10x) + 1
        /// </summary>
        static public float ExponentialEaseOut(float p)
        {
            return (p == 1.0f) ? p : 1 - Math.Pow(2, -10 * p);
        }

        /// <summary>
        /// Modeled after the piecewise exponential
        /// y = (1/2)2^(10(2x - 1))         ; [0,0.5)
        /// y = -(1/2)*2^(-10(2x - 1))) + 1 ; [0.5,1]
        /// </summary>
        static public float ExponentialEaseInOut(float p)
        {
            if (p == 0.0 || p == 1.0) return p;

            if (p < 0.5f)
            {
                return 0.5f * Math.Pow(2, (20 * p) - 10);
            }
            else
            {
                return -0.5f * Math.Pow(2, (-20 * p) + 10) + 1;
            }
        }

        /// <summary>
        /// Modeled after the damped sine wave y = sin(13pi/2*x)*Math.Pow(2, 10 * (x - 1))
        /// </summary>
        static public float ElasticEaseIn(float p)
        {
            return Math.Sin(13 * HALFPI * p) * Math.Pow(2, 10 * (p - 1));
        }

        /// <summary>
        /// Modeled after the damped sine wave y = sin(-13pi/2*(x + 1))*Math.Pow(2, -10x) + 1
        /// </summary>
        static public float ElasticEaseOut(float p)
        {
            return Math.Sin(-13 * HALFPI * (p + 1)) * Math.Pow(2, -10 * p) + 1;
        }

        /// <summary>
        /// Modeled after the piecewise exponentially-damped sine wave:
        /// y = (1/2)*sin(13pi/2*(2*x))*Math.Pow(2, 10 * ((2*x) - 1))      ; [0,0.5)
        /// y = (1/2)*(sin(-13pi/2*((2x-1)+1))*Math.Pow(2,-10(2*x-1)) + 2) ; [0.5, 1]
        /// </summary>
        static public float ElasticEaseInOut(float p)
        {
            if (p < 0.5f)
            {
                return 0.5f * Math.Sin(13 * HALFPI * (2 * p)) * Math.Pow(2, 10 * ((2 * p) - 1));
            }
            else
            {
                return 0.5f * (Math.Sin(-13 * HALFPI * ((2 * p - 1) + 1)) * Math.Pow(2, -10 * (2 * p - 1)) + 2);
            }
        }

        /// <summary>
        /// Modeled after the overshooting cubic y = x^3-x*sin(x*pi)
        /// </summary>
        static public float BackEaseIn(float p)
        {
            return p * p * p - p * Math.Sin(p * PI);
        }

        /// <summary>
        /// Modeled after overshooting cubic y = 1-((1-x)^3-(1-x)*sin((1-x)*pi))
        /// </summary>	
        static public float BackEaseOut(float p)
        {
            float f = (1 - p);
            return 1 - (f * f * f - f * Math.Sin(f * PI));
        }

        /// <summary>
        /// Modeled after the piecewise overshooting cubic function:
        /// y = (1/2)*((2x)^3-(2x)*sin(2*x*pi))           ; [0, 0.5)
        /// y = (1/2)*(1-((1-x)^3-(1-x)*sin((1-x)*pi))+1) ; [0.5, 1]
        /// </summary>
        static public float BackEaseInOut(float p)
        {
            if (p < 0.5f)
            {
                float f = 2 * p;
                return 0.5f * (f * f * f - f * Math.Sin(f * PI));
            }
            else
            {
                float f = (1 - (2 * p - 1));
                return 0.5f * (1 - (f * f * f - f * Math.Sin(f * PI))) + 0.5f;
            }
        }

        /// <summary>
        /// </summary>
        static public float BounceEaseIn(float p)
        {
            return 1 - BounceEaseOut(1 - p);
        }

        /// <summary>
        /// </summary>
        static public float BounceEaseOut(float p)
        {
            if (p < 4 / 11.0f)
            {
                return (121 * p * p) / 16.0f;
            }
            else if (p < 8 / 11.0f)
            {
                return (363 / 40.0f * p * p) - (99 / 10.0f * p) + 17 / 5.0f;
            }
            else if (p < 9 / 10.0f)
            {
                return (4356 / 361.0f * p * p) - (35442 / 1805.0f * p) + 16061 / 1805.0f;
            }
            else
            {
                return (54 / 5.0f * p * p) - (513 / 25.0f * p) + 268 / 25.0f;
            }
        }

        /// <summary>
        /// </summary>
        static public float BounceEaseInOut(float p)
        {
            if (p < 0.5f)
            {
                return 0.5f * BounceEaseIn(p * 2);
            }
            else
            {
                return 0.5f * BounceEaseOut(p * 2 - 1) + 0.5f;
            }
        }

        //goes from 0 -> 1 -> 0
        static public float PingPong(float p)
        {
            if (p <= .5f)
            {
                return p * 2f;
            }
            else
            {
                return 1f - 2 * (p - .5f);
            }
        }
    }
}

SquashController.cs

using Core.Utils;
using System.Collections.Generic;
using UnityEngine;

namespace Core.Movement
{
    public class SquashController : HashSet<Squash>
    {
        public float SquashAmt;
        public Transform SquashTarget;

        public SquashController(Transform trans, float amt)
        {
            this.SquashTarget = trans;
            this.SquashAmt = amt;
        }

        Queue<Squash> removeQueue = new Queue<Squash>();
        public void Update(float dt)
        {
            Vector2 buffer = Vector2.zero;
            foreach( var s in this)
            {
                s.Update(dt);
                if (s.IsComplete)
                    removeQueue.Enqueue(s);
                buffer += s.Value;
            }

            while (removeQueue.Count > 0)
            {
                var removal = removeQueue.Dequeue();
                if (removal.Next != null)
                    this.Add(removal.Next);
                this.Remove(removal);
            }

            var targetSquash = new Vector3(1 + buffer.x * SquashAmt, 1 + buffer.y * SquashAmt, 1f);
            SquashTarget.localScale = targetSquash;
        }

    }
    
    public class Squash
    {
        public float Duration;
        private Vector2 StartAlpha;

        public Vector2 EndAlpha;

        private Easing.Functions EaseFunc;
        public static Vector2 Wide = new Vector2(1f, -1f);
        public static Vector2 Thin = new Vector2(-1f, 1f);
        public static Vector2 Zero = new Vector2(0f, 0f);

        public Squash Next;
        
        float Alpha => Mathf.Clamp01(accum / Duration);
        float EasedAlpha {
            get {
                return Easing.Interpolate(Alpha, EaseFunc);
            }
        }

        public bool IsComplete => Alpha == 1f;
        float accum = 0f;

        public Vector2 Value {
            get {
                return Vector2.LerpUnclamped(StartAlpha, EndAlpha, EasedAlpha);
            }
        }
        
        public Squash(float duration, Vector2 startAlpha, Vector2 endAlpha, float axisNoise = 0f, Easing.Functions func = Easing.Functions.ElasticEaseOut)
        {
            Duration = duration;
            this.StartAlpha = startAlpha;
            if(axisNoise != 0f)
            {
                var noise =  UnityEngine.Random.Range(-axisNoise, axisNoise);
                StartAlpha.x += noise;
                StartAlpha.y -= noise;
            }
            this.EndAlpha = endAlpha;
            this.EaseFunc = func;
        }

        public Squash(float duration, Vector2 endAlpha, Easing.Functions func = Easing.Functions.ElasticEaseOut)
        {
            Duration = duration;
            this.StartAlpha = Zero;
            this.EndAlpha = endAlpha;
            this.EaseFunc = func;
        }

        public Squash Then(Squash next)
        {
            this.Next = next;
            this.Next.StartAlpha = this.EndAlpha;
            return this;
        }

        public void Update(float dt)
        {
            accum += dt;
        }


    }

}