I do not follow your logic. In mathematics, in Cartesian nD coordinate system, a point is represented by a set of distances between that point and the centre of coordinates, along each axe. Just like a vector. And vectorA + vectorB is a very common operation.
RD> Yes, a point is taken w.r.t. the centre coordinates, but that does not RD> mean that it behaves like a vector. All that means is that it is RD> identifying a position in nD space, for example, a button is at (3,4) RD> from a frame's client area. And vector in nD space is ... identifying a position in nD space. Just like a point. The difference is very vague and depends on the particular topic you are working on. RD> If you look up Point at MathWorld RD> (http://mathworld.wolfram.com/Point.html) there is no reference to RD> adding two points together, whereas for vectors RD> (http://mathworld.wolfram.com/Vector.html) there is. Once again, we are talking about Cartesian coordinates, and in this particular case, point and vector are practically the same thing. In many books/articles, etc. points are treated exactly the same as vectors. Now, there might be completely different reasons for treating points and sizes differently in a C++ program, and that would be the type safety. But if we go in this direction, we might as well introduce a type for velocity, to be able to do something like this: void on_timer(time t) { velocity vel = getvelocity(); position pos = guiobject.pos(); move(guiobject, pos + (t - prev_t) * vel); prev_t = t; } Valentin Samko http://val.samko.info