Re: missing button release event?

[Damon Chaplin <damon karuna eclipse co uk>]

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.

Damon