Ballistics.h

static inline bool intersectbox(const vec &o, const vec &rad, const vec &from, const vec &to, vec *end) // if lineseg hits entity bounding box
{
    const vec *p;
    vec v = to, w = o;
    v.sub(from);
    w.sub(from);
    float c1 = w.dot(v);

    if(c1<=0) p = &from;
    else
    {
        float c2 = v.squaredlen();
        if(c2<=c1) p = &to;
        else
        {
            float f = c1/c2;
            v.mul(f).add(from);
            p = &v;
        }
    }

    if(p->x <= o.x+rad.x
       && p->x >= o.x-rad.x
       && p->y <= o.y+rad.y
       && p->y >= o.y-rad.y
       && p->z <= o.z+rad.z
       && p->z >= o.z-rad.z)
    {
        if(end) *end = *p;
        return true;
    }
    return false;
}

static inline bool intersectsphere(const vec &from, const vec &to, vec center, float radius, float &dist)
{
    vec ray(to);
    ray.sub(from);
    center.sub(from);
    float v = center.dot(ray),
          inside = radius*radius - center.squaredlen();
    if(inside < 0 && v < 0) return false;
    float raysq = ray.squaredlen(), d = inside*raysq + v*v;
    if(d < 0) return false;
    dist = (v - sqrtf(d)) / raysq;
    return dist >= 0 && dist <= 1;
}

static inline bool intersectcylinder(const vec &from, const vec &to, const vec &start, const vec &end, float radius, float &dist)
{
    vec d(end), m(from), n(to);
    d.sub(start);
    m.sub(start);
    n.sub(from);
    float md = m.dot(d),
          nd = n.dot(d),
          dd = d.squaredlen();
    if(md < 0 && md + nd < 0) return false;
    if(md > dd && md + nd > dd) return false;
    float nn = n.squaredlen(),
          mn = m.dot(n),
          a = dd*nn - nd*nd,
          k = m.squaredlen() - radius*radius,
          c = dd*k - md*md;
    if(fabs(a) < 0.005f)
    {
        if(c > 0) return false;
        if(md < 0) dist = -mn / nn;
        else if(md > dd) dist = (nd - mn) / nn;
        else dist = 0;
        return true;
    }
    else if(c > 0)
    {
        float b = dd*mn - nd*md,
              discrim = b*b - a*c;
        if(discrim < 0) return false;
        dist = (-b - sqrtf(discrim)) / a;
    }
    else dist = 0;
    float offset = md + dist*nd;
    if(offset < 0)
    {
        if(nd <= 0) return false;
        dist = -md / nd;
        if(k + dist*(2*mn + dist*nn) > 0) return false;
    }
    else if(offset > dd)
    {
        if(nd >= 0) return false;
        dist = (dd - md) / nd;
        if(k + dd - 2*md + dist*(2*(mn-nd) + dist*nn) > 0) return false;
    }
    return dist >= 0 && dist <= 1;
}