easing.h

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#pragma once
#include "ga/math.h"
#include <functional>
#include <vector>
 
namespace ga {
 
using EasingFn = std::function<float( float )>;
 
namespace ease {
 
    //
    // standardized easing / tweening functions -
    //      p = f(t)
    //
    //      convert 't' time (percent 0-1) to 'p' position (percent 0-1)
    //      based on an easing curve - see http://robertpenner.com/easing/penner_chapter7_tweening.pdf
    //
 
    // exponential curves
    // ------------------
    // https://github.com/jesusgollonet/ofpennereasing/blob/master/PennerEasing/Expo.cpp
 
    inline float expoIn( float t )
    {  // t is percent (0.-1.) of transition
        return ( t == 0.0f ) ? 0.0f : pow( 2.0f, 10.0f * ( t - 1.0f ) );
    }
 
    inline float expoOut( float t )
    {
        return ( t == 1.0f ) ? 1.0f : 1.0f - pow( 2.0f, -10.0f * t );
    }
 
    inline float expoInOut( float t )
    {
        if ( t == 0.0f ) {
            return 0.0f;
        }
 
        if ( t == 1.0f ) {
            return 1.0f;
        }
 
        if ( ( t /= 0.5f ) < 1.0f ) {
            return 0.5f * pow( 2.0f, 10.0f * ( t - 1.0f ) );
        }
 
        return 0.5f * ( -pow( 2.0f, -10.0f * --t ) + 2.0f );
    }
 
    // cubic / quadratic curves
    // ------------------------
 
    inline float cubeInQuadOut( float t )
    {
        if ( t < 0.5f ) {
            return 4.0f * t * t * t;
        }  // cubic in
 
        return ( -2.0f * t * t ) + ( 4.0f * t ) - 1.0f;  // quadratic out
    }
 
    // material design curves
    // ----------------------
    // https://material.io/design/motion/speed.html#easing
 
    // Material "standard ease" (decelerate in, accelerate out)
    inline float material( float t )
    {
        return cubicBezier( t, 0.4f, 0.0f, 0.2f, 1.0f );
    }
 
    // Material "accelerate" (e.g. exit screen)
    inline float materialEnter( float t )
    {
        return cubicBezier( t, 0.0f, 0.0f, 0.2f, 1.0f );
    }
 
    // Material "decelerate" (e.g. enter screen)
    inline float materialExit( float t )
    {
        return cubicBezier( t, 0.4f, 0.0f, 1.0f, 1.0f );
    }
}  // namespace ease
 
enum class EaseType
{
    LINEAR,
    EXPO_IN,
    EXPO_OUT,
    EXPO_IN_OUT,
    CUBE_IN_QUAD_OUT,
    MATERIAL,
    MATERIAL_ENTER,
    MATERIAL_EXIT,
    CUSTOM,
    // for loops:
    NUM_TYPES,
    DEFAULT = LINEAR,
};
 
inline std::function<float( float )> easeFn( const EaseType& type )
{
    using namespace ease;
    switch ( type ) {
        case EaseType::EXPO_IN:
            return expoIn;
        case EaseType::EXPO_OUT:
            return expoOut;
        case EaseType::EXPO_IN_OUT:
            return expoInOut;
        case EaseType::CUBE_IN_QUAD_OUT:
            return cubeInQuadOut;
        case EaseType::MATERIAL:
            return material;
        case EaseType::MATERIAL_ENTER:
            return materialEnter;
        case EaseType::MATERIAL_EXIT:
            return materialExit;
        case EaseType::LINEAR:
        default:
            return []( float t ) { return t; };
    }
}
 
}  // namespace ga