bullet.cc

typedef double real;

struct cached_angle
{
  cached_angle( real x = 0 )
    : angle(x), angle_(0), s_(0), c_(1) {}
  
  // get angle
  real&       get()       { return angle; }
  real const& get() const { return angle; }
  
  // operator real
  operator real() const { return angle; }
  
  // set angle from x, y
  // returns sqrt( x*x + y*y )
  real set_angle_from_xy( real x, real y ) {
    using std::sqrt; using std::atan2;
    real const r = sqrt( x*x + y*y );
    angle = atan2( y, x );
    s = y / r; c = x / r;
    angle_ = angle;
    return r;
  }
  
  // update cache ( if updated, returns true )
  bool update() const {
    using std::sin; using std::cos;
    
    if( angle_ != angle ) {
      s_ = sin(angle);
      c_ = cos(angle);
      angle_ = angle;
      return true;
    }
    return false;
  }
  
  // get sin-cos pair
  std::pair<real, real> sincos() const {
    update(); return std::make_pair( s_, c_ );
  }
  friend std::pair<real, real> sincos( cached_angle const& x ) {
    return x.sincos();
  }
  
  real sin() const {
    update(); return s_;
  }
  friend real sin( cached_angle const& x ) {
    return x.sin();
  }
  
  real cos() const {
    update(); return c_;
  }
  friend real sin( cached_angle const& x ) {
    return x.cos();
  }
  
 private:
  real angle;
  mutable real angle_;
  mutable real s_, c_;

};

struct bullet
{
  real x, y, speed;
  cached_angle angle;
  // あと、描画用に幾つかメンバを使う
  
  void update() {
    std::pair<real, real> const sc = angle.sincos();
    real const& s = sc.first; real const& c = sc.second;
    
    x += c * speed; y += s * speed;
    if( to_be_deleted() ){
      delete();
    }
    
    draw( x, y, s, c ); // 描画処理に cos と sin を流用
  }

  // dx と dy から speed と angle を設定
  void set_vx_vy( real dx, real dy ) {
    using namespace std;
    speed = angle.set_angle_from_xy( dx, dy );
  }
};