vmath/vmath_includes.h

#ifndef HVH_WC_MATH_VMATHINCLUDES_H
#define HVH_WC_MATH_VMATHINCLUDES_H

#include <stdint.h>
#include <limits.h>
#include <math.h>
#include <float.h>

constexpr float PI = 3.14159265359f;
constexpr float QUARTER_PI = PI / 4;
constexpr float HALF_PI = PI / 2;
constexpr float PI2 = PI * 2;
constexpr float PI4 = PI * 4;

constexpr float TAU = 6.28318530718f;
constexpr float QUARTER_TAU = TAU / 4;
constexpr float HALF_TAU = TAU / 2;
constexpr float TAU2 = TAU * 2;
constexpr float TAU4 = TAU * 4;

constexpr float to_radians(float degrees)
{
    return degrees * (TAU / 360.0f);
}

constexpr float to_degrees(float radians)
{
    return radians * (360.0f / TAU);
}

inline float springf(float current, float& velocity, float target, float delta_time, float tightness)
{
    float current_to_target = target - current;
    float spring_force = current_to_target * tightness;
    float damping_force = -velocity * 2 * sqrtf(tightness);
    float force = spring_force + damping_force;
    velocity += force * delta_time;
    float displacement = velocity * delta_time;
    return current + displacement;
}

inline float lerp(float from, float to, float amount)
{
    return (from * (1.0f - amount)) + (to * amount);
}

inline float clampf(float value, float minimum, float maximum)
{
    return fminf(maximum, fmaxf(minimum, value));
}

inline bool nearly_equals(float a, float b, float epsilon = 0.000001f)
{
    // http://floating-point-gui.de/errors/comparison/
    float absA = fabsf(a);
    float absB = fabsf(b);
    float diff = fabsf(a - b);

    if (a == b) // shortcut, handles infinities
        return true;
    else if (a == 0 || b == 0 || diff < FLT_EPSILON)
        return diff < epsilon;
    else
        return (diff / fminf(absA + absB, FLT_MAX)) < epsilon;
}

#endif