Re: missing button release event?

[Paul Emsley <paul emsley bioch ox ac uk>]

On 07/11/2012 12:05 AM, Damon Chaplin wrote:
> On Tue, 2012-07-10 at 23:40 +0100, Paul Emsley wrote:
> > On 10/07/12 20:33, Damon Chaplin wrote:
> > > On Tue, 2012-07-10 at 17:48 +0100, Paul Emsley wrote:
> > > > Hi,
> > > >
> > > > When I create a goocanvas
> > > >
> > > >       GtkWidget *canvas = goo_canvas_new();
> > > >       GooCanvas *gc = GOO_CANVAS(canvas);
> > > >
> > > > I then attached callbacks to it...
> > > >
> > > >          ... other callbacks ...
> > > >          g_signal_connect(G_OBJECT(goo_canvas_get_root_item(gc)),
> > > >                   "button_release_event",
> > > >                   G_CALLBACK(on_canvas_button_release), NULL);
> > > >
> > > >      This works fine almost all the time - however, there is one operation
> > > > (a line addition) where the on_canvas_button_release callback doesn't
> > > > get called (I added a print statement in it to check).  I can't think
> > > > why it might not be being called.  Can you help?
> > > >
> > > > Cheers,
> > > >
> > > > Paul.
> > > >
> > > > p.s. code here: http://coot.googlecode.com/svn/trunk/lbg/lbg.cc
> > > Are you creating an item underneath the mouse when the button is
> > > pressed? The button release event may be being sent to that new item and
> > > ignored.
> > >
> > > I can't think of any other reason at the moment. It would be handy if
> > > GooCanvas had some debugging support for events - i.e. output where
> > > events are being sent.
> > Hi Damon,
> >
> > Thanks for your prompt reply.
> >
> > Yes, I am creating an item under the mouse (at least potentially).  The
> > new line (a chemical bond, FWIW) changes (or can change) the text for
> > the atom (under the cursor).
> >
> > I thought I had checked for that though by adding a button release
> > callback specifically when text is created.  Maybe I missed one/some.  Hmm.
> >
> > Why is it that for this operation the callback is attached (or is at
> > least potentially attached) to the new text item, but for most other
> > mouse events (motion and button-down, for example) attaching callbacks
> > to the canvas works fine?
> >
> > Is it more likely that the callback is attached to the text under the
> > cursor that gets deleted or the text under the cursor that is newly
> > created?  Maybe if I created a text group to handle this and added and
> > deleted items from the group - would that be better do you think?
> It shouldn't be that complicated.
>
> I think you just need to check all your button release callbacks and
> make sure they only return TRUE when they handled the event.
> If they return TRUE it stops the event from propagating up to parent
> items.

Hi Damon,

That's encouraging, thanks.

If I click on an item, drag to plain canvas and button-up, what should 
get the button-up callback, canvas or item?

If I click on an item (as as a result, the item is deleted), drag to 
plain canvas and button up, what (if anything) received the button-up 
callback? (In my case it seems nothing).

Cheers,

Paul.