A single file tween library in C# with support built in for XNA and Unity data types. MIT License.

TinyTween.cs

// TinyTween.cs
//
// Copyright (c) 2013 Nick Gravelyn
//
// Permission is hereby granted, free of charge, to any person obtaining a copy of this software
// and associated documentation files (the "Software"), to deal in the Software without restriction,
// including without limitation the rights to use, copy, modify, merge, publish, distribute,
// sublicense, and/or sell copies of the Software, and to permit persons to whom the Software is
// furnished to do so, subject to the following conditions:
//
// The above copyright notice and this permission notice shall be included in all copies or substantial
// portions of the Software.
//
// THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR IMPLIED, INCLUDING BUT
// NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT.
// IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY,
// WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION WITH THE
// SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.
//

// For Unity, we can check all the individual platform defines to infer the environment.
#if UNITY_EDITOR || UNITY_STANDALONE_OSX || UNITY_DASHBOARD_WIDGET || UNITY_STANDALONE_WIN || UNITY_STANDALONE_LINUX || UNITY_WEBPLAYER || UNITY_WII || UNITY_IPHONE || UNITY_ANDROID || UNITY_PS3 || UNITY_XBOX360 || UNITY_NACL || UNITY_FLASH
#define UNITY
#else
// For XNA, you can either go into the project and add 'XNA' to the Build defines list or you can uncomment the following line.
//#define XNA
#endif

using System;

// XNA and Unity have such similar APIs we can use the same code by just swapping the namespaces.
#if XNA
using Microsoft.Xna.Framework;
#elif UNITY
using UnityEngine;
#endif

namespace TinyTween
{
    /// <summary>
    /// Takes in progress which is the percentage of the tween complete and returns
    /// the interpolation value that is fed into the lerp function for the tween.
    /// </summary>
    /// <remarks>
    /// Scale functions are used to define how the tween should occur. Examples would be linear,
    /// easing in quadratic, or easing out circular. You can implement your own scale function
    /// or use one of the many defined in the ScaleFuncs static class.
    /// </remarks>
    /// <param name="progress">The percentage of the tween complete in the range [0, 1].</param>
    /// <returns>The scale value used to lerp between the tween's start and end values</returns>
    public delegate float ScaleFunc(float progress);

    /// <summary>
    /// Standard linear interpolation function: "start + (end - start) * progress"
    /// </summary>
    /// <remarks>
    /// In a language like C++ we wouldn't need this delegate at all. Templates in C++ would allow us
    /// to simply write "start + (end - start) * progress" in the tween class and the compiler would
    /// take care of enforcing that the type supported those operators. Unfortunately C#'s generics
    /// are not so powerful so instead we must have the user provide the interpolation function.
    ///
    /// Thankfully frameworks like XNA and Unity provide lerp functions on their primitive math types
    /// which means that for most users there is nothing specific to do here. Additionally this file
    /// provides concrete implementations of tweens for vectors, colors, and more for XNA and Unity
    /// users, lessening the burden even more.
    /// </remarks>
    /// <typeparam name="T">The type to interpolate.</typeparam>
    /// <param name="start">The starting value.</param>
    /// <param name="end">The ending value.</param>
    /// <param name="progress">The interpolation progress.</param>
    /// <returns>The interpolated value, generally using "start + (end - start) * progress"</returns>
    public delegate T LerpFunc<T>(T start, T end, float progress);

    /// <summary>
    /// State of an ITween object
    /// </summary>
    public enum TweenState
    {
        /// <summary>
        /// The tween is running.
        /// </summary>
        Running,

        /// <summary>
        /// The tween is paused.
        /// </summary>
        Paused,

        /// <summary>
        /// The tween is stopped.
        /// </summary>
        Stopped
    }

    /// <summary>
    /// The behavior to use when manually stopping a tween.
    /// </summary>
    public enum StopBehavior
    {
        /// <summary>
        /// Does not change the current value.
        /// </summary>
        AsIs,

        /// <summary>
        /// Forces the tween progress to the end value.
        /// </summary>
        ForceComplete
    }

    /// <summary>
    /// Interface for a tween object.
    /// </summary>
    public interface ITween
    {
        /// <summary>
        /// Gets the current state of the tween.
        /// </summary>
        TweenState State { get; }

        /// <summary>
        /// Pauses the tween.
        /// </summary>
        void Pause();

        /// <summary>
        /// Resumes the paused tween.
        /// </summary>
        void Resume();

        /// <summary>
        /// Stops the tween.
        /// </summary>
        /// <param name="stopBehavior">The behavior to use to handle the stop.</param>
        void Stop(StopBehavior stopBehavior);

        /// <summary>
        /// Updates the tween.
        /// </summary>
        /// <param name="elapsedTime">The elapsed time to add to the tween.</param>
        void Update(float elapsedTime);
    }

    /// <summary>
    /// Interface for a tween object that handles a specific type.
    /// </summary>
    /// <typeparam name="T">The type to tween.</typeparam>
    public interface ITween<T> : ITween
        where T : struct
    {
        /// <summary>
        /// Gets the current value of the tween.
        /// </summary>
        T CurrentValue { get; }

        /// <summary>
        /// Starts a tween.
        /// </summary>
        /// <param name="start">The start value.</param>
        /// <param name="end">The end value.</param>
        /// <param name="duration">The duration of the tween.</param>
        /// <param name="scaleFunc">A function used to scale progress over time.</param>
        void Start(T start, T end, float duration, ScaleFunc scaleFunc);
    }

    /// <summary>
    /// A concrete implementation of a tween object.
    /// </summary>
    /// <typeparam name="T">The type to tween.</typeparam>
    public class Tween<T> : ITween<T>
        where T : struct
    {
        private readonly LerpFunc<T> lerpFunc;

        private float currentTime;
        private float duration;
        private ScaleFunc scaleFunc;
        private TweenState state;

        private T start;
        private T end;
        private T value;

        /// <summary>
        /// Gets the current time of the tween.
        /// </summary>
        public float CurrentTime { get { return currentTime; } }

        /// <summary>
        /// Gets the duration of the tween.
        /// </summary>
        public float Duration { get { return duration; } }

        /// <summary>
        /// Gets the current state of the tween.
        /// </summary>
        public TweenState State { get { return state; } }

        /// <summary>
        /// Gets the starting value of the tween.
        /// </summary>
        public T StartValue { get { return start; } }

        /// <summary>
        /// Gets the ending value of the tween.
        /// </summary>
        public T EndValue { get { return end; } }

        /// <summary>
        /// Gets the current value of the tween.
        /// </summary>
        public T CurrentValue { get { return value; } }

        /// <summary>
        /// Initializes a new Tween with a given lerp function.
        /// </summary>
        /// <remarks>
        /// C# generics are good but not good enough. We need a delegate to know how to
        /// interpolate between the start and end values for the given type.
        /// </remarks>
        /// <param name="lerpFunc">The interpolation function for the tween type.</param>
        public Tween(LerpFunc<T> lerpFunc)
        {
            this.lerpFunc = lerpFunc;
            state = TweenState.Stopped;
        }

        /// <summary>
        /// Starts a tween.
        /// </summary>
        /// <param name="start">The start value.</param>
        /// <param name="end">The end value.</param>
        /// <param name="duration">The duration of the tween.</param>
        /// <param name="scaleFunc">A function used to scale progress over time.</param>
        public void Start(T start, T end, float duration, ScaleFunc scaleFunc)
        {
            if (duration <= 0)
            {
                throw new ArgumentException("duration must be greater than 0");
            }
            if (scaleFunc == null)
            {
                throw new ArgumentNullException("scaleFunc");
            }

            currentTime = 0;
            this.duration = duration;
            this.scaleFunc = scaleFunc;
            state = TweenState.Running;

            this.start = start;
            this.end = end;

            UpdateValue();
        }

        /// <summary>
        /// Pauses the tween.
        /// </summary>
        public void Pause()
        {
            if (state == TweenState.Running)
            {
                state = TweenState.Paused;
            }
        }

        /// <summary>
        /// Resumes the paused tween.
        /// </summary>
        public void Resume()
        {
            if (state == TweenState.Paused)
            {
                state = TweenState.Running;
            }
        }

        /// <summary>
        /// Stops the tween.
        /// </summary>
        /// <param name="stopBehavior">The behavior to use to handle the stop.</param>
        public void Stop(StopBehavior stopBehavior)
        {
            state = TweenState.Stopped;

            if (stopBehavior == StopBehavior.ForceComplete)
            {
                currentTime = duration;
                UpdateValue();
            }
        }

        /// <summary>
        /// Updates the tween.
        /// </summary>
        /// <param name="elapsedTime">The elapsed time to add to the tween.</param>
        public void Update(float elapsedTime)
        {
            if (state != TweenState.Running)
            {
                return;
            }

            currentTime += elapsedTime;
            if (currentTime >= duration)
            {
                currentTime = duration;
                state = TweenState.Stopped;
            }

            UpdateValue();
        }

        /// <summary>
        /// Helper that uses the current time, duration, and delegates to update the current value.
        /// </summary>
        private void UpdateValue()
        {
            value = lerpFunc(start, end, scaleFunc(currentTime / duration));
        }
    }

    /// <summary>
    /// Object used to tween float values.
    /// </summary>
    public class FloatTween : Tween<float>
    {
        private static float LerpFloat(float start, float end, float progress) { return start + (end - start) * progress; }

        // Static readonly delegate to avoid multiple delegate allocations
        private static readonly LerpFunc<float> LerpFunc = LerpFloat;

        /// <summary>
        /// Initializes a new FloatTween instance.
        /// </summary>
        public FloatTween() : base(LerpFunc) { }
    }

    // If XNA or Unity we can leverage their types to create more tween types to simplify usage.
#if XNA || UNITY
    /// <summary>
    /// Object used to tween Vector2 values.
    /// </summary>
    public class Vector2Tween : Tween<Vector2>
    {
        // Static readonly delegate to avoid multiple delegate allocations
        private static readonly LerpFunc<Vector2> LerpFunc = Vector2.Lerp;

        /// <summary>
        /// Initializes a new Vector2Tween instance.
        /// </summary>
        public Vector2Tween() : base(LerpFunc) { }
    }

    /// <summary>
    /// Object used to tween Vector3 values.
    /// </summary>
    public class Vector3Tween : Tween<Vector3>
    {
        // Static readonly delegate to avoid multiple delegate allocations
        private static readonly LerpFunc<Vector3> LerpFunc = Vector3.Lerp;

        /// <summary>
        /// Initializes a new Vector3Tween instance.
        /// </summary>
        public Vector3Tween() : base(LerpFunc) { }
    }

    /// <summary>
    /// Object used to tween Vector4 values.
    /// </summary>
    public class Vector4Tween : Tween<Vector4>
    {
        // Static readonly delegate to avoid multiple delegate allocations
        private static readonly LerpFunc<Vector4> LerpFunc = Vector4.Lerp;

        /// <summary>
        /// Initializes a new Vector4Tween instance.
        /// </summary>
        public Vector4Tween() : base(LerpFunc) { }
    }

    /// <summary>
    /// Object used to tween Color values.
    /// </summary>
    public class ColorTween : Tween<Color>
    {
        // Static readonly delegate to avoid multiple delegate allocations
        private static readonly LerpFunc<Color> LerpFunc = Color.Lerp;

        /// <summary>
        /// Initializes a new ColorTween instance.
        /// </summary>
        public ColorTween() : base(LerpFunc) { }
    }

    /// <summary>
    /// Object used to tween Quaternion values.
    /// </summary>
    public class QuaternionTween : Tween<Quaternion>
    {
        // Static readonly delegate to avoid multiple delegate allocations
        private static readonly LerpFunc<Quaternion> LerpFunc = Quaternion.Lerp;

        /// <summary>
        /// Initializes a new QuaternionTween instance.
        /// </summary>
        public QuaternionTween() : base(LerpFunc) { }
    }
#endif

    /// <summary>
    /// Defines a set of premade scale functions for use with tweens.
    /// </summary>
    /// <remarks>
    /// To avoid excess allocations of delegates, the public members of ScaleFuncs are already
    /// delegates that reference private methods.
    ///
    /// Implementations based on http://theinstructionlimit.com/flash-style-tweeneasing-functions-in-c
    /// which are based on http://www.robertpenner.com/easing/
    /// </remarks>
    public static class ScaleFuncs
    {
        /// <summary>
        /// A linear progress scale function.
        /// </summary>
        public static readonly ScaleFunc Linear = LinearImpl;

        /// <summary>
        /// A quadratic (x^2) progress scale function that eases in.
        /// </summary>
        public static readonly ScaleFunc QuadraticEaseIn = QuadraticEaseInImpl;

        /// <summary>
        /// A quadratic (x^2) progress scale function that eases out.
        /// </summary>
        public static readonly ScaleFunc QuadraticEaseOut = QuadraticEaseOutImpl;

        /// <summary>
        /// A quadratic (x^2) progress scale function that eases in and out.
        /// </summary>
        public static readonly ScaleFunc QuadraticEaseInOut = QuadraticEaseInOutImpl;

        /// <summary>
        /// A cubic (x^3) progress scale function that eases in.
        /// </summary>
        public static readonly ScaleFunc CubicEaseIn = CubicEaseInImpl;

        /// <summary>
        /// A cubic (x^3) progress scale function that eases out.
        /// </summary>
        public static readonly ScaleFunc CubicEaseOut = CubicEaseOutImpl;

        /// <summary>
        /// A cubic (x^3) progress scale function that eases in and out.
        /// </summary>
        public static readonly ScaleFunc CubicEaseInOut = CubicEaseInOutImpl;

        /// <summary>
        /// A quartic (x^4) progress scale function that eases in.
        /// </summary>
        public static readonly ScaleFunc QuarticEaseIn = QuarticEaseInImpl;

        /// <summary>
        /// A quartic (x^4) progress scale function that eases out.
        /// </summary>
        public static readonly ScaleFunc QuarticEaseOut = QuarticEaseOutImpl;

        /// <summary>
        /// A quartic (x^4) progress scale function that eases in and out.
        /// </summary>
        public static readonly ScaleFunc QuarticEaseInOut = QuarticEaseInOutImpl;

        /// <summary>
        /// A quintic (x^5) progress scale function that eases in.
        /// </summary>
        public static readonly ScaleFunc QuinticEaseIn = QuinticEaseInImpl;

        /// <summary>
        /// A quintic (x^5) progress scale function that eases out.
        /// </summary>
        public static readonly ScaleFunc QuinticEaseOut = QuinticEaseOutImpl;

        /// <summary>
        /// A quintic (x^5) progress scale function that eases in and out.
        /// </summary>
        public static readonly ScaleFunc QuinticEaseInOut = QuinticEaseInOutImpl;

        /// <summary>
        /// A sinusoidal progress scale function that eases in.
        /// </summary>
        public static readonly ScaleFunc SineEaseIn = SineEaseInImpl;

        /// <summary>
        /// A sinusoidal progress scale function that eases out.
        /// </summary>
        public static readonly ScaleFunc SineEaseOut = SineEaseOutImpl;

        /// <summary>
        /// A sinusoidal progress scale function that eases in and out.
        /// </summary>
        public static readonly ScaleFunc SineEaseInOut = SineEaseInOutImpl;

        private const float Pi = (float)Math.PI;
        private const float HalfPi = Pi / 2f;

        private static float LinearImpl(float progress) { return progress; }
        private static float QuadraticEaseInImpl(float progress) { return EaseInPower(progress, 2); }
        private static float QuadraticEaseOutImpl(float progress) { return EaseOutPower(progress, 2); }
        private static float QuadraticEaseInOutImpl(float progress) { return EaseInOutPower(progress, 2); }
        private static float CubicEaseInImpl(float progress) { return EaseInPower(progress, 3); }
        private static float CubicEaseOutImpl(float progress) { return EaseOutPower(progress, 3); }
        private static float CubicEaseInOutImpl(float progress) { return EaseInOutPower(progress, 3); }
        private static float QuarticEaseInImpl(float progress) { return EaseInPower(progress, 4); }
        private static float QuarticEaseOutImpl(float progress) { return EaseOutPower(progress, 4); }
        private static float QuarticEaseInOutImpl(float progress) { return EaseInOutPower(progress, 4); }
        private static float QuinticEaseInImpl(float progress) { return EaseInPower(progress, 5); }
        private static float QuinticEaseOutImpl(float progress) { return EaseOutPower(progress, 5); }
        private static float QuinticEaseInOutImpl(float progress) { return EaseInOutPower(progress, 5); }

        private static float EaseInPower(float progress, int power)
        {
            return (float)Math.Pow(progress, power);
        }

        private static float EaseOutPower(float progress, int power)
        {
            int sign = power % 2 == 0 ? -1 : 1;
            return (float)(sign * (Math.Pow(progress - 1, power) + sign));
        }

        private static float EaseInOutPower(float progress, int power)
        {
            progress *= 2;
            if (progress < 1)
            {
                return (float)Math.Pow(progress, power) / 2f;
            }
            else
            {
                int sign = power % 2 == 0 ? -1 : 1;
                return (float)(sign / 2.0 * (Math.Pow(progress - 2, power) + sign * 2));
            }
        }

        private static float SineEaseInImpl(float progress)
        {
            return (float)Math.Sin(progress * HalfPi - HalfPi) + 1;
        }

        private static float SineEaseOutImpl(float progress)
        {
            return (float)Math.Sin(progress * HalfPi);
        }

        private static float SineEaseInOutImpl(float progress)
        {
            return (float)(Math.Sin(progress * Pi - HalfPi) + 1) / 2;
        }
    }
}