Re: on_expose_event and drawingarea redrawing issues

[Robert Caryl <bob fis-cal com>]

Hey Will:

Instead of overriding Gtk::Window::on_expose_event, just create a slot
like this:

bool MainMenu::my_expose_event(GdkEventExpose* e) {

    Glib::RefPtr<Gdk::Pixbuf> tmpimage = image->scale_simple(da->get_width(),
            da->get_height(),Gdk::INTERP_BILINEAR);
   tmpimage->render_to_drawable(da->get_window(),da->get_style()->get_white_gc(),   
        0, 0, 0, 0,da->get_width(),da->get_height(),Gdk::RGB_DITHER_NONE, 0, 0);
    Gtk::Window::on_expose_event(event);
    return true;

}

and then connect to your Gtk::DrawingArea object's
Gtk::DrawingArea::signal_expose_event using that function.  I think
you'll find that it will do what you want and will not exhibit the
strange behavior you described.

Bob

Will Megee wrote:
> I have a drawing area consisting of a background image, and I'm using
> the function below to redraw the image on resize or any other expose
> event. The MainMenu class inherits from
> Gtk::Window. The issue I'm having is that the image does not redraw
> properly until the window is iconified and deiconified. If the window is
> the image will become progressively darker and darker until it is nearly
> black. If a menu is drawn on top of the area either the problem above
> will happen or the area under will become blank (white). Once the window
> gets iconified and deiconified the DrawingArea has a normal appearance.
> My background image is compiled directly into a library at runtime
> rather than reading in from disk. I believe it was originally a PNG with
> alpha transparency. I have noticed that if I use another transparent XPM
> and create the pixbuf from a file statically this does not occur - the
> redrawing works perfectly.
>
> I am not using the DrawingArea anywhere else in the program except for
> the constructor and this function. There are no signals bound to the
> DrawingArea or image. I've tried binding the signal like so:
> da->signal_expose_event().connect(sigc::mem_fun(*this,&MainMenu::on_expose_event));
>
> and it doesn't appear to change anything.
>
> //da is a Gtk::DrawingArea, image is a Glib::RefPtr<Gdk::Pixbuf>
> //MainMenu inherits from Gtk::Window
>
> bool MainMenu::on_expose_event(GdkEventExpose* event)
> {
>     Glib::RefPtr<Gdk::Pixbuf> tmpimage =
> image->scale_simple(da->get_width(),
>             da->get_height(),Gdk::INTERP_BILINEAR);
>    tmpimage->render_to_drawable(da->get_window(),
> da->get_style()->get_white_gc(),   
>         0, 0, 0, 0,
> da->get_width(),da->get_height(),Gdk::RGB_DITHER_NONE, 0, 0);
>     Gtk::Window::on_expose_event(event);
>     return true;
> }
>
> I also tried using the full scale() function and got the same result. So
> my question is, does the problem lie in my on_expose_event function, or
> the compiled image i'm using, or somewhere else? My coworker who
> originally created the image library thinks it could be a bug in gtkmm
> or possibly the window manager or something more fundamental than my
> program.
>
> Thanks,
>
> Will Megee
> Software Engineer
> Fiscal Systems
> will fis-cal com
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