光线与球的求交代码

//-------------------------------------------------------------------------
eiBool eiSphere::intersect(eiRay *ray, eiObject *po, eiFloat & oldt,
                            eiPrimitive* & ret_pri, eiFloat *cust_data,
                            HitParam *hparam)
{
    if( oldt == 0.0f || ray_box( ray->src, hparam->hitPoint )
    {
        //compute intersecting point

        eiVector    oc = add( ray->src, - center );
        eiFloat        oc_len = dist( oc );
            
        if( oc_len > radius || po->material->doubleSide )
        {
            eiFloat    a = dot( ray->dir, ray->dir );
            eiFloat    b = 2.0f * dot( oc, ray->dir);
            eiFloat    c = dot( oc, oc ) - RR;
            eiFloat    dt = b * b - 4.0f * a * c;

            eiFloat    t;

            if(a == 0.0f || dt < 0.0f)
                return false;
            else if(dt == 0.0f)
            {
                t = - b / a * 0.5f;

                if(t < 0.0f)
                    return false;
            }
            else
            {
                a = 0.5f / a;
                eiFloat t1 = (- b + sqrtf( dt )) * a;
                eiFloat t2 = (- b - sqrtf( dt )) * a;

                if(t1 > 0.0f && t2 < 0.0f)
                    t = t1;
                else if(t1 < 0.0f && t2 > 0.0f)
                    t = t2;
                else if(t1 > 0.0f && t2 > 0.0f)
                    t = (t1 < t2) ? t1 : t2;
                else
                    return false;
            }

            eiVector tmpIntersection = add(ray->src, mulvf(ray->dir,t));

            //affect shadow factor

            if(ray->type == RAY_SHADOW)
                hparam->shadow_factor *= 1.0f - po->material->opacity;

            //find nearest hit point

            if(oldt == 0.0f || t < oldt)
            {
                hparam->hitPoint = tmpIntersection;
                hparam->hitObj = po;
                ret_pri = this;
                oldt = t;

                //fill custom data

                return true;
            }
        }
    }

    return false;
}