onb.h

#ifndef ORTHO_NORMAL_BASIS_H_
#define ORTHO_NORMAL_BASIS_H_

#include "ray.h"
class onb
{
public:
    onb() {}
    inline vec3 operator[](int i) const { return axis[i]; }
    vec3 u() const { return axis[0]; }
    vec3 v() const { return axis[1]; }
    vec3 w() const { return axis[2]; }
    vec3 local(double a, double b, double c) const { return a * u() + b * v() + c * w(); }
    vec3 local(const vec3& a) const { return a.x() * u() + a.y() * v() + a.z() * w(); }
    void build_from_w(const vec3&);
    vec3 axis[3];
};


void onb::build_from_w(const vec3& n) {
    axis[2] = unit_vector(n);
    vec3 a;
    if (fabs(w().x()) > 0.9)
        a = vec3(0, 1, 0);
    else
        a = vec3(1, 0, 0);
    axis[1] = unit_vector(cross(w(), a));
    axis[0] = cross(w(), v());
}
#endif