Re: [Gtk2hs-users] Heavy CPU use by X server with onMotionNotify + redrawing

[Axel S. <Axe...@en...>]

On Thu, 2008-07-10 at 20:29 +1000, Chris Mears wrote:
> Axel Simon <Axe...@en...> writes:
> 
> > You have to pass in the DrawWindow of the enclosing Window widget. I
> > don't quite understand why, but here's an alternative to your program
> > without using the IORef:
> >
> >   G.onExposeRect da $ const $ do
> >    dw <- G.widgetGetDrawWindow w
> >    mPos <- G.drawWindowGetPointer dw
> >    case mPos of
> >     Just (_, x, y, _) -> do
> >       dw <- G.widgetGetDrawWindow da
> >       gc <- G.gcNew dw
> >       G.drawRectangle dw gc True (x-5) (y-5) 10 10
> >     Nothing -> return ()
> >
> > Axel.
> 
> Hi Axel,
> 
> Thanks for your speedy reply.  This alone isn't quite what I want,
> because it updates the rectangle's position only on expose events --
> should it be combined with something to regularly generate expose
> events?

The only time you should draw to the canvas is in the onExpose signal.
If you need to update the widget's contents periodically, you should
just generate a new onExpose signal by calling widgetRedrawAll from a
timer. (See earlier email on the Cairo clock example).

Axel.