27     Vector2D v(mX, mY);  in copy()  local
28     return v;  in copy()
31 void Vector2D::add(const Vector2D& v) {  in add()  argument
32     mX += v.mX;  in add()
33     mY += v.mY;  in add()
36 void Vector2D::sub(const Vector2D& v) {  in sub()  argument
37     mX -= v.mX;  in sub()
38     mY -= v.mY;  in sub()
46 float Vector2D::distance(const Vector2D& v) {  in distance()  argument
47     float dx = mX - v.mX;  in distance()
48     float dy = mY - v.mY;  in distance()