Re: Drawing with cairo

["Diego A. Fons" <diegofons apexar com>]

Theodore Papadopoulo wrote:
> Igor Gorbounov wrote:
>   
> > Diego A. Fons пишет:
> >   
> >     
> > > [...]
> > > My question is if there is a way of preserve the cairo context intact 
> > > between the the calls to on_expose_event()? Why getting the cairo 
> > > context in the on_realize() handler and storing it in a variable doesn't 
> > > work?
> > >   
> > >     
> > >       
> > Why, it works! Those are just examples. I use a context variable
> > as a member of my Plot class, and this variable is assigned in
> > an initialization method, and reassigned when plot area is resized.
> >     Igor Gorbounov
> >
> >   
> >     
> Strange because I have kind of the same experience as Diego...
>
> At least using gtk-- and storing the cairo context obtained at
> configure time (maybe not at realization time, I have tried many 
> variants I do
> not remember if I tried that variant), to use it in the handling of 
> expose events
> just did not work. I had to request a new cairo context for each expose 
> events.
>
> I never had time to fully investigate the problem, but I certainly had a 
> similar experience...
>
>     Theo.
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>
>   
Hi,

Like Theodore I'm using gtkmm. This is an extrac of the code which 
doesn't work:
void Plotter::on_realize( void )
{
   // Create the GDK window
   refGdkWindow = Gdk::Window::create(get_window(), &attributes,
           GDK_WA_X | GDK_WA_Y);

   // Create Cairo context
   Cairo::RefPtr<Cairo::Context> cr = refGdkWindow->create_cairo_context();
}


bool Plotter::on_expose_event( GdkEventExpose* event )
{
   // ... Use cr to do some drawing
}

Both cr and refGdkWindow are members of the class Plotter. Instead if i 
do this everything goes fine:

void Plotter::on_realize( void )
{
   // Create the GDK window
   refGdkWindow = Gdk::Window::create(get_window(), &attributes,
           GDK_WA_X | GDK_WA_Y);
}

bool Plotter::on_expose_event( GdkEventExpose* event )
{
   // Get cr to do some drawing
   Cairo::RefPtr<Cairo::Context> cr = refGdkWindow->create_cairo_context();

   // Do some drawing ...
}

The last code works fine and i can implement it, but i prefer not 
redrawing all the graph because performance issues, I'm developing this 
application for an embedded device.

So, if anyone can see what's wrong in the first code or just explain me 
(us) why i can't do that, you are wellcome!

Regards,
Diego A. Fons.