Class ProjectilePath

plugins/siege-engine.cpp:795–845

 */

struct ProjectilePath {
    static const int DEFAULT_FUDGE = 31;

    df::coord origin, goal, target, fudge_delta;
    int divisor, fudge_factor;
    df::coord speed, direction;

    ProjectilePath(df::coord origin, df::coord goal) :
        origin(origin), goal(goal), fudge_factor(1)
    {
        fudge_delta = df::coord(0,0,0);
        calc_line();
    }

    ProjectilePath(df::coord origin, df::coord goal, df::coord delta, int factor) :
        origin(origin), goal(goal), fudge_delta(delta), fudge_factor(factor)
    {
        calc_line();
    }

    ProjectilePath(df::coord origin, df::coord goal, float zdelta, int factor = DEFAULT_FUDGE) :
        origin(origin), goal(goal), fudge_factor(factor)
    {
        fudge_delta = df::coord(0,0,int(factor * zdelta));
        calc_line();
    }

    void calc_line()
    {
        speed = goal - origin;
        speed.x *= fudge_factor;
        speed.y *= fudge_factor;
        speed.z *= fudge_factor;
        speed = speed + fudge_delta;
        target = origin + speed;
        divisor = point_distance(speed);
        if (divisor <= 0) divisor = 1;
        direction = df::coord(speed.x>=0?1:-1,speed.y>=0?1:-1,speed.z>=0?1:-1);
    }

    df::coord operator[] (int i) const
    {
        int div2 = divisor * 2;
        int bias = divisor-1;
        return origin + df::coord(
            (2*speed.x*i + direction.x*bias)/div2,
            (2*speed.y*i + direction.y*bias)/div2,
            (2*speed.z*i + direction.z*bias)/div2
        );
    }
};

static ProjectilePath decode_path(lua_State *L, int idx, df::coord origin)
{