Re: [gtkmm] Problem with refreshing a DrawingArea in a multi-threaded program

[MHL Schulze t-online de (Martin Schulze)]

Am 18.07.2002 21:08 schrieb(en) Johan Rutgeerts:
>  Hi,
>
> I'm having a problem realising some program with Gtkmm, and I don't
> manage
> to
> solve it! (don't have all too much programming experience, actually, and
> never
> mind Gtkmm experience). Maybe one of you can help me...
>
> I'm writing a program to visualize data from a laserscanner. I'm using a
>
> Gtkmm::DrawingArea to draw points at coordinates that I get from the
> laserscanner.
>
> The laserscanner is implemented as an active object. It inherits from
> some
> class "EventSource".
>
> For the DrawingArea, I wrote a derived class "LaserArea", which inherits
> from
> "DrawingArea" and "EventListener". Being an EventListener, the laserarea
> has
> a
> member function "onEvent(Event& e)", and can be attached to an
> EventSource
> (in
> this case the laserscanner).
>
> Whenever the laserscanner has new data, it calls the "onEvent" of the
> laserarea. This causes the new data to be copied to the laserarea, and
> then
> it
> calls draw_laserview(), which does the actual drawing of the points:
>
>
> void LaserArea::onEvent(MoRE_utilities::Event& event)
> {
>   _mutex.acquire();
>     for(unsigned int i = 0; i < _nrOfRanges; i++ )
>     {
>       _range[i] =
> _laserscanner->rangeDouble(i);
> //_range, _cartx and _carty are arrays of doubles
>       _cartx[i] = _range[i] * sin(PI/180 * double(i)/2 - _angle);
>       _carty[i] = _range[i] * cos(PI/180 * double(i)/2 - _angle);
>     }
>   _mutex.release();
>
>   draw_laserview();

No, don't ever draw without request from the gtk event system!
Override Gtk::DrawingErea::on_expose_event() and do all drawing there.
Call quere_draw() or queue_draw_area() whenever you need to refresh
the contents of the widget.

Also you shouldn't mess around with mutexes in you gui specific code.
The gtk event loop is quite sensitive! If you need to manipulate the
gui from within another thread look at the Glib::Dispatcher stuff. I
haven't tried it yet but it is the right way to access the one and only
gui thread with the running gtk event loop and to trigger events there.

Regards,

  Martin