Re: signal_button_press_event() not sending signal?

On Sun, 2004-12-19 at 22:59 +0100, Antonio Coralles wrote:
> Matthew Ryan Hurne wrote:
> > First of all, let me hint that I am very new to Gtkmm programming, and
> > relatively new to C++ programming in general.
> >
> > I am trying to write a simple program that draws a bezier curve in a
> > DrawingArea which can be manipulated by clicking and dragging its
> > control points.
> >
> > Right now the program draws a curve, but I have not yet successfully
> > implemented anything to manipulate it.  That's what I'm working on.
> >
> > I figured I'd start by figuring out how to detect a button click on the
> > DrawingArea.  I know I'll need to get the coordinates of the mouse
> > pointer as well.  From reading the tutorial, etc. it seemed that
> > Widget::signal_button_press_event() is the appropriate method to use.  I
> > have connected it to a signal handler in my MainWindow class.
> > Everything compiles fine but the code in my signal handler doesn't seem
> > to execute.
> >
> > Here's what code it seems you'd need.
> > In MainWindow's constructor (curveArea is my DrawingArea):
> >
> > curveArea.signal_button_press_event().connect(sigc::mem_fun(*this,
> > &MainWindow::on_curve_button_press_event));
> >
> > A protected member of MainWindow:
> >
> > bool MainWindow::on_curve_button_press_event(GdkEventButton* event)
> > {
> >         std::cout << "The drawing area was clicked" << std::endl;
> >
> >         return true;
> > }
> >
> > I searched the web for a while trying to find any hints, and was only
> > able to find something on a mailing list from 2002 that said it was a
> > bug.  Seems like that wouldn't be relevant anymore.  Any help would be
> > greatly appreciated.  If you want all my source code, I can attach it in
> > a future e-mail.  I wasn't sure if that was proper mailing list
> > etiquette so I figured I'd leave it out in this message.  Oh and one
> > more thing...I'm having a lot of fun learning all this stuff.  :-)
> >
> > Matthew Hurne
> >
> > _______________________________________________
> > gtkmm-list mailing list
> > gtkmm-list gnome org <mailto:>
> >
> I would suggest you to read 
> To 
> detect mouse clicks i would override bool 
> Gtk::Widget::on_button_press_event(GdkEventButton*  event)  ... For 
> further documentation for the various GdkEvent structs you may look at 
> antonio
> _______________________________________________
> gtkmm-list mailing list
> gtkmm-list gnome org

Thanks for the tip on reading chapter 14, though I've already done that.
I have been able to draw the curve, control points, and lines connected
the control points just fine.  I haven't coded the interaction between
the mouse and the curve, that's where I'm at now.

Thanks a TON for the link to the GDK event structures.  Though right now
I can't use it because it seems the mouse clicks aren't even being
"detected", it will definitely be important when it comes to checking
the mouse position and whether a control point has been clicked.

I did what you suggested, or at least what I think you suggested, with
no results.  I have inherited my own class, called CurveArea, from
DrawingArea.  I overloaded its on_button_press_event(GdkEventButton
*event) member with the following:

bool CurveArea::on_button_press_event(GdkEventButton* event)
	if (event->type == GDK_BUTTON_PRESS && event->button == 1) {
		std::cout << "The drawing area was clicked"
                          << std::endl;

	return true;

Here is the relevant line in CurveArea's constructor:


I'm guessing I don't need the this->, but I figured being explicit
couldn't hurt.

When clicking on the CurveArea, nothing is printed to the console.
Help! Ahh!

Oh, by the way, why does on_button_press_event have to return a bool?

Matthew Hurne

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