Re: Drawing with cairo

[Igor Gorbounov <igor gorbounov gmail com>]

Diego A. Fons пишет:

[...]

Still I don't understand why can't get a context and store it in a 
member variable.

  

[...]

Then look here:
this is Plot class definition:

class Plot
{
public:
    Plot(Cairo::RefPtr<Cairo::Context>& context, Gdk::Rectangle& plotarea);
    ~Plot();
    std::vector<Series*> series;
...
private:
    Cairo::RefPtr<Cairo::Context> plot_context;
    Gdk::Color background_color, foreground_color;
....
};

Plot constructor:

Plot::Plot(Cairo::RefPtr<Cairo::Context>& context, Gdk::Rectangle& pltarea)
{
    plotarea = pltarea;
    marginrect = Gdk::Rectangle(int(0.03*plotarea.get_width()), int(0.03*plotarea.get_height()),
        int(0.94*plotarea.get_width()), int(0.94*plotarea.get_height()));
    plotrect = marginrect;
    plot_context = context;
    background_color = Gdk::Color("white");
...
}

Plot resizing:

void Plot::resize(Cairo::RefPtr<Cairo::Context>& context, Gdk::Rectangle& pltarea)
{ // необходимые действия при изменении размера
    plot_context = context;
    plotarea = pltarea;
    plot_context->set_source_rgb(background_color.get_red(), background_color.get_green(), background_color.get_blue());
...
}

And this is plot initialization from MainWindow:
void Mainwindow::plot_init(void)
{ // начальная настройка графика
    plotarea_win = drawingarea->get_window();
...
    win_context->set_source_rgb(color.get_red(), color.get_green(), color.get_blue());
    //prepare a copy
    plotareaCopy = Gdk::Pixmap::create(plotarea_win, drawingarea->get_allocation().get_width(),
      drawingarea->get_allocation().get_height(), -1);
    gc = Gdk::GC::create(plotarea_win);//sorry...
    cairo = plotareaCopy->create_cairo_context();
    int pwidth, pheight;
    plotareaCopy->get_size(pwidth, pheight);
    Gdk::Rectangle plot_area = Gdk::Rectangle(0, 0, pwidth, pheight);
    plot = new Plot(cairo, plot_area);
    ....
    drawingarea->signal_expose_event().connect(
        sigc::mem_fun(*this, &Mainwindow::on_drawingarea_expose_event));
}

This is an expose event - sorry, but for the sake of speed I use here Gdk::GC approach
for simple copying of area from a background copy:

bool Mainwindow::on_drawingarea_expose_event(GdkEventExpose *event)
{ 
    plotarea_win->draw_drawable(gc, plotareaCopy, event->area.x, event->area.y,
        event->area.x, event->area.y, event->area.width, event->area.height);

   ...
  return true;
}

And here is resizing of a plot:
bool Mainwindow::on_drawingarea_configure_event(GdkEventConfigure*)
{ // redefine demensions
    plotareaCopy = Gdk::Pixmap::create(plotarea_win,
        drawingarea->get_allocation().get_width(), drawingarea->get_allocation().get_height(), -1);
    if (plot)
        {
        cairo = plotareaCopy->create_cairo_context();
        int pwidth, pheight;
        plotareaCopy->get_size(pwidth, pheight);
        Gdk::Rectangle plot_area = Gdk::Rectangle(0, 0, pwidth, pheight);
        plot->resize(cairo, plot_area);
        plot->drawplots();
        }
   
  return true;
}

When I need printing I just call Plot::resize(Cairo::RefPt...) with the context and rectangle
taken from Gtk::PrintContext.

   Hope it helps somewhat,
      Igor Gorbounov