IAPDemo/Libraries/cocos2d/cocos/rparticle/Math/Random/Random.h

//
//  Random.h
//  cocos2d_libs
//
//  Created by 徐俊杰 on 2020/5/25.
//

#ifndef Random_h
#define Random_h

#include "rparticle/Math/Random/rand.h"
//#include "Runtime/Math/Vector2.h"
//#include "Runtime/Math/Quaternion.h"
#include "rparticle/Math/FloatConversion.h"

NS_RRP_BEGIN

inline float RangedRandom (Rand& r, float min, float max)
{
    float t = r.GetFloat ();
    t = min * t + (1.0F - t) * max;
    return t;
}

inline float Random01 (Rand& r)
{
    return r.GetFloat ();
}

inline int RangedRandom (Rand& r, int min, int max)
{
    int dif;
    if (min < max)
    {
        dif = max - min;
        int t = r.Get () % dif;
        t += min;
        return t;
    }
    else if (min > max)
    {
        dif = min - max;
        int t = r.Get () % dif;
        t = min - t;
        return t;
    }
    else
    {
        return min;
    }
}

inline Vector3f RandomUnitVector (Rand& rand)
{
    float z = RangedRandom (rand, -1.0f, 1.0f);
    float a = RangedRandom (rand, 0.0f, 2.0F * kPI);
    
    float r = sqrt (1.0f - z*z);
    
    float x = r * cos (a);
    float y = r * sin (a);
    
    return Vector3f (x, y, z);
}

inline Vector2f RandomUnitVector2 (Rand& rand)
{
    float a = RangedRandom (rand, 0.0f, 2.0F * kPI);
    
    float x = cos (a);
    float y = sin (a);
    
    return Vector2f (x, y);
}


inline Quaternionf RandomQuaternion (Rand& rand)
{
    Quaternionf q;
    q.x = RangedRandom (rand, -1.0f, 1.0f);
    q.y = RangedRandom (rand, -1.0f, 1.0f);
    q.z = RangedRandom (rand, -1.0f, 1.0f);
    q.w = RangedRandom (rand, -1.0f, 1.0f);
    q = NormalizeSafe (q);
    if (Dot (q, Quaternionf::identity ()) < 0.0f)
        return -q;
    else
        return q;
}

inline Quaternionf RandomQuaternionUniformDistribution (Rand& rand)
{
    const float two_pi = 2.0F * kPI;
    
    // Employs Hopf fibration to uniformly distribute quaternions
    float u1 = RangedRandom( rand, 0.0f, 1.0f );
    float theta = RangedRandom( rand, 0.0f, two_pi );
    float rho = RangedRandom( rand, 0.0f, two_pi );
    
    float i = sqrt( 1.0f - u1 );
    float j = sqrt( u1 );
    
    // We do not need to normalize the generated quaternion, because the probability density corresponds to the Haar measure.
    // This means that a random rotation is obtained by picking a point at random on S^3, and forming the unit quaternion.
    Quaternionf q( i * sin(theta), i * cos(theta), j * sin(rho), j * cos(rho) );
    
    if (Dot (q, Quaternionf::identity ()) < 0.0f)
        return -q;
    else
        return q;
}


inline Vector3f RandomPointInsideCube (Rand& r, const Vector3f& extents)
{
    return Vector3f (    RangedRandom (r, -extents.x, extents.x),
                     RangedRandom (r, -extents.y, extents.y),
                     RangedRandom (r, -extents.z, extents.z));
}

inline Vector3f RandomPointBetweenCubes (Rand& r, const Vector3f& min, const Vector3f& max)
{
    Vector3f v;
    int i;
    for (i=0;i<3;i++)
    {
        float x = r.GetFloat () * 2.0F - 1.0F;
        if (x > 0.0f)
            v[i] = min[i] + x * (max[i] - min[i]);
        else
            v[i] = -min[i] + x * (max[i] - min[i]);
    }
    return v;
}

inline Vector3f RandomPointInsideUnitSphere (Rand& r)
{
    Vector3f v = RandomUnitVector (r);
    v *= pow (Random01 (r), 1.0F / 3.0F);
    return v;
}

inline Vector3f RandomPointInsideEllipsoid (Rand& r, const Vector3f& extents)
{
    return ScaleVec3 (RandomPointInsideUnitSphere (r), extents);
}

inline Vector3f RandomPointBetweenSphere (Rand& r, float minRadius, float maxRadius)
{
    Vector3f v = RandomUnitVector (r);
    // As the volume of the sphere increases (x^3) over an interval we have to increase range as well with x^(1/3)
    float range = pow (RangedRandom (r, 0.0F, 1.0F), 1.0F / 3.0F);
    return v * (minRadius + (maxRadius - minRadius) * range);
}

inline Vector2f RandomPointInsideUnitCircle (Rand& r)
{
    Vector2f v = RandomUnitVector2 (r);
    // As the volume of the sphere increases (x^3) over an interval we have to increase range as well with x^(1/3)
    v *= pow (RangedRandom (r, 0.0F, 1.0F), 1.0F / 2.0F);
    return v;
}

inline Vector3f RandomPointBetweenEllipsoid (Rand& r, const Vector3f& maxExtents, float minRange)
{
    Vector3f v = ScaleVec3 (RandomUnitVector (r), maxExtents);
    // As the volume of the sphere increases (x^3) over an interval we have to increase range as well with x^(1/3)
    float range = pow (RangedRandom (r, minRange, 1.0F), 1.0F / 3.0F);
    return v * range;
}

/// Builds a random Barycentric coordinate which can be used to generate random points on a triangle:
/// Vector3f point = v0 * barycentric.x + v1 * barycentric.y + v2 * barycentric.z;
inline Vector3f RandomBarycentricCoord (Rand& rand)
{
    // Was told that this leads to bad distribution because of the 1.0F - s
    //    float s = gRand.GetFloat ();
    //    float t = RangedRandom (gRand, 0.0F, 1.0F - s);
    //    float r = (1.0F - s - t);
    //    Vector3f positionOnMesh = r * vertices[face.v1] + s * vertices[face.v2] + t * vertices[face.v3];
    //    return positionOnMesh;
    float u = rand.GetFloat ();
    float v = rand.GetFloat ();
    if (u + v > 1.0F)
    {
        u = 1.0F - u;
        v = 1.0F - v;
    }
    float w = 1.0F - u - v;
    return Vector3f (u, v, w);
}

NS_RRP_END

#endif /* Random_h */