Movable objects around a wxPanel

Question

In wxWidgets, I would like to have 2 objects on a wxPanel joined by a line and with a mouse down event to relocate the position of either of the 2 objects (The line should automatically be redrawn to follow the new position of the objects). I have tried using wxPaintDC to draw the initial position of the 2 objects (Custom created with mouse click events) and using dc.DrawLine to join these 2 objects together with a line. How should I proceed to allow make those 2 objects movable (mouse down event) along with the line? Can this even be achieve?

Answer 1

Of course it's possible (just about everything is, it's "only" a matter of effort), but it's not completely trivial and you may want to use OGL which does it for you. On the flip side, OGL is very old and completely unmaintained since a long time, so if your needs are really simple, it's probably still better to do it yourself.

If you do, here are some hints:

1. For mouse handling, you first need an (efficient if possible) hit testing function.
2. Once you have it, it's easy to detect where a click happens and what object is under it and start moving it if it makes sense. To be more user friendly, the move shouldn't start immediately, but wait until either the mouse moves a little, or stays pressed for some longer time (this will avoid accidental moves).
3. When the user is dragging the mouse you will get wxEVT_MOTION events. Use wxMouseEvent::Dragging() in your handler to check whether any mouse button is pressed.
4. Whatever you do, you must always draw from your wxEVT_PAINT handler, i.e. if an object moves, you must not redraw it immediately, but update its position, invalidate the area taken by it before and after the move (invalidating everything is simpler, but less efficient) and draw it from your OnPaint().
5. You want double buffering to avoid flicker, see wxAutoBufferedPaintDC