EasingFunctions.cs

namespace Gondwana.Physics.Movement.Easing;

public static class EasingFunctions
{
    public static float Linear(float t) => t;

    public static float EaseInQuad(float t) => t * t;

    public static float EaseOutQuad(float t) => t * (2f - t);

    public static float EaseInOutQuad(float t)
    {
        t *= 2f;
        if (t < 1f) return 0.5f * t * t;
        t -= 1f;
        return -0.5f * (t * (t - 2f) - 1f);
    }

    public static float EaseInCubic(float t) => t * t * t;

    public static float EaseOutCubic(float t)
    {
        t -= 1f;
        return t * t * t + 1f;
    }

    public static float EaseInOutCubic(float t)
    {
        t *= 2f;
        if (t < 1f) return 0.5f * t * t * t;
        t -= 2f;
        return 0.5f * (t * t * t + 2f);
    }

    public static float EaseInQuart(float t) => t * t * t * t;

    public static float EaseOutQuart(float t)
    {
        t -= 1f;
        return 1f - t * t * t * t;
    }

    public static float EaseInOutQuart(float t)
    {
        t *= 2f;
        if (t < 1f) return 0.5f * t * t * t * t;
        t -= 2f;
        return -0.5f * (t * t * t * t - 2f);
    }

    public static float EaseInQuint(float t) => t * t * t * t * t;

    public static float EaseOutQuint(float t)
    {
        t -= 1f;
        return t * t * t * t * t + 1f;
    }

    public static float EaseInOutQuint(float t)
    {
        t *= 2f;
        if (t < 1f) return 0.5f * t * t * t * t * t;
        t -= 2f;
        return 0.5f * (t * t * t * t * t + 2f);
    }

    public static float SmoothStep(float t) => t * t * (3f - 2f * t);

    public static float SmootherStep(float t) => t * t * t * (t * (t * 6f - 15f) + 10f);

    public static Func<float, float> From(EasingKind kind)
    {
        return kind switch
        {
            EasingKind.Linear => Linear,
            EasingKind.EaseInQuad => EaseInQuad,
            EasingKind.EaseOutQuad => EaseOutQuad,
            EasingKind.EaseInOutQuad => EaseInOutQuad,
            EasingKind.EaseInCubic => EaseInCubic,
            EasingKind.EaseOutCubic => EaseOutCubic,
            EasingKind.EaseInOutCubic => EaseInOutCubic,
            EasingKind.EaseInQuart => EaseInQuart,
            EasingKind.EaseOutQuart => EaseOutQuart,
            EasingKind.EaseInOutQuart => EaseInOutQuart,
            EasingKind.EaseInQuint => EaseInQuint,
            EasingKind.EaseOutQuint => EaseOutQuint,
            EasingKind.EaseInOutQuint => EaseInOutQuint,
            EasingKind.SmoothStep => SmoothStep,
            EasingKind.SmootherStep => SmootherStep,
            _ => Linear
        };
    }
}