[java-gnome-hackers] How to deal with MotionNotifyEvent?

[Vreixo F. L. <met...@ya...>]

Hi everybody,

I need to expose motion-notify-event Widget signal to use it in an app. 
This event, however, is only received after "activating" it, i.e.,
passing the GDK_POINTER_MOTION_MASK to the gdk_window_set_events, that
of course requires a GdkWindow to be available.

I've seen that for VisibilityNotifyEvent, that also requires similar
procedure, you take care of that internally, hidden for the user. That
is great!

However, for motion notify I don't know if that is a good idea. It
generates a lot of events, while usually you only take care about them
sometimes. For example, in my application I use this event to move a
chart on a cairo drawing area when the user keeps the left button
pressed. However, if the user release the button I do not care about
this event at all. If I enable it when connecting to the signal, I will
receive a lot of events in my app. In my opinion, it is better to allow
users to enable/disable such kind of events when needed.

However, the enable/disable procedure is rather complex, and ugly, as it
requires knowledge about the underlying GdkWindow details. If event
signals are part of Widget, I think enable/disable should be there. My
proposal would be to add a pair of methods to Widget:

enableEvent()
disableEvent()

that take a EventMask as parameter. Such methods would get the
GdkWindow, realizing the widget if needed (as you do in
GtkWidgetOverride for visibility event), and enable/disable the given
events, left the other events untouched. Then, events such as motion
notify should document the procedure. This way, underlying details are
hidden for the user.

In my opinion, that would be much easy to understand for users. However,
it has a problem, too, as if two widget share the same GdkWindow, the
behavior of enable/disable methods could be confusing. Anyway, I think
that good documentation can explain this.

What do you think? Do you like the idea? 

Cheers
Vreixo



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