Thanks. I've spent many hours on debugging this, but could not find a solution.
Your answer encouraged me to look again and do strange tests. That led me to
find the bug in my code.
> blue146 wrote:
> > I have a class that derives from Fl_Group, and contains several widgets.
> > When I call activate() for one of the deactivated widgets (Fl_Round_Button
> > for instance) then somehow draw() is called for the whole Fl_Group class.
> > This causes the group to flicker on the screen once. I guess that it
> > flickers because it takes some time to redraw all of the widgets in the
> > group.
> > Do you know how could I stop the whole group from redrawing when I change
> > just one of it's children ? Optimally, only the changed widget should be
> > redrawn.
>
> No idea, since the default Fl_Widget::activate()
> only tells that widget to redraw:
>
> void Fl_Widget::activate() {
> if (!active()) {
> clear_flag(INACTIVE);
> if (active_r()) {
> redraw();
> redraw_label();
> handle(FL_ACTIVATE);
> if (inside(Fl::focus())) Fl::focus()->take_focus();
> }
> }
> }
>
> Possibly there's other code involved causing the redraw of
> the parent. Note label is redrawn, as well as an "FL_ACTIVATE"
> event sent to the widget's handle() method.
>
> Regarding the 'flicker', try using Fl_Double_Window if possible
> instead of Fl_Window; it uses double buffering which prevents flicker,
> whereas Fl_Window is single buffered.
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