Re: drawables and refresh rates

[Carl Nygard <cjnygard fast net>]

On Sat, 2004-12-04 at 01:04, Rob Benton wrote:
> Carl Nygard wrote:
> > On Fri, 2004-12-03 at 04:43, Andrew E. Makeev wrote:
> > 
> >>Rob Benton wrote:
> >>
> >>
> >>>Andrew E. Makeev wrote:
> >>>
> >>>
> >>>>Before to answer you, we need to know how do you "draw" your circles? 
> >>>>The common way is to use expose_event to redraw only those parts of 
> >>>>the drawing area that actually were changed. In this case I never 
> >>>>seen any flickering in my applications even on Celeron 300Mhz.
> >>>>
> >>>
> >>>Right now I'm using 2 methods.  Method A handles the expose event of 
> >>>the Gtk::DrawingArea which then calls method B.  Method B is also 
> >>>connected to the value changed signal of both the Gtk::HScale widgets.
> >>>
> > 
> > 
> > I do something like:
> > 
> > Method A handles expose events, and redraws exposed rectangle from
> > internal pixmap.
> > 
> > Method B connected to value changed signal, draws to internal pixmap,
> > calls queue_draw() which eventually triggers Method A.
> > 
> 
> Carl I did some reading on double buffering.  Where I've been stuck is
> that in order to start drawing to a Gdk::Drawable, it has to be realized
> first.  Pixmap looks like what I need but its create methods all take a 
> Glib::RefPtr<Gdk::Drawable>.  And I get a segfault when I try that.
> 
> > You can add efficiency by keeping track of the bounding box of what you
> > redraw, and only trigger expose events for those rectangles.
> > 
> 
> How would I do that?  I have 1 drawing area widget which
> is 100x100.  I draw a complete blue circle and then a red arc on top of
> that.  Finally, to smooth out the edges I load an svg which is a smooth
> black circle outline.  The flickering comes even if I don't use
> window->clear() just b/c each draw command overlaps the previous one.
> 

Hooking into the expose_event should work.  Gtk takes care of the double
buffering itself.  I think it's automatic, but I could be wrong...

Just create the pixmap and draw to it first time through the expose
callback?  Or some other ugly hack, I don't remember the answer.  Could
be hook into configure event, or realize event.  There's examples on
this because allocating colors has the same sort of problem.


    // .. create widgets

    _widg->signal_expose_event().
        connect(SigC::slot(*this, &GtkScreen::_ExposeCB));

     //  initialization

     _widg->queue_draw();