Re: Fatal IO error 104 when using Gtk::Context::show_text

[Jonathon Jongsma <jonathon quotidian org>]

On Wed, 2007-11-14 at 01:48 -0800, Jake Brownson wrote:
> See below for a small program to recreate the problem.
> 
> The window just flashes up and then I quickly get:
> "Fatal IO error 104 (Connection reset by peer) on X server :0.0."
> 
> If I use a debugger the crash happens on the line with the show_text
> call, but I don't seem to get a signal, the app just crashes.
> 
> I tried going through pango to draw text and see the same problem. I
> sent this to a friend (who runs the same distro and version I do) and
> he had the same problem. I also tried setting up all the font settings
> like in example code that comes with libcairomm, but that didn't seem
> to help.
> 
> Am I doing something wrong? or is this a bug?
> 
> I'm using Ubuntu 7.10, gtkmm 2.12.0, gtk 2.12.0, pango 1.18.3
> 
> #include <gtkmm.h>
> #include <cairomm/cairomm.h>
> 
> class CairoDrawer : public Gtk::DrawingArea
> {
> public:
> 	virtual bool on_expose_event(GdkEventExpose*)
> 	{
> 		Cairo::RefPtr<Cairo::Context> c = get_window()->create_cairo_context();
> 		Gtk::Allocation allocation = get_allocation();
> 		c->scale(allocation.get_width(), allocation.get_height());
> 		c->move_to(0, 0);
> 		c->show_text("Crash Here");
> 		return true;
> 	}
> };
> 
> int main(int argc, char *argv[])
> {
> 	Gtk::Main kit(argc, argv);
> 	Gtk::Window window;
> 	CairoDrawer cairo_drawer;
> 	cairo_drawer.show();
> 	window.add(cairo_drawer);

As far as I can tell this is because when you call Cairo::scale(), it
doesn't seem to affect the font scale, so it is trying to draw a huge
font (e.g. the default font size of 10 or 12 multiplied by the size of
the window (~200), so it's trying to draw a font size of approximately
2000, and I guess X has problems with that).  So you must explicitly set
the font size after scaling the context.  But even with that, it
wouldn't show anything, because your move_to() sets the current point to
the top left corner of the window, and the call to show_text() will make
the text extend right and up, which will be outside of the boundary of
the window, so you need to change the move_to() so that the text gets
drawn within the window.  The following code should work.

#include <gtkmm.h>
#include <cairomm/cairomm.h>

class CairoDrawer : public Gtk::DrawingArea
{
public:
        virtual bool on_expose_event(GdkEventExpose*)
        {
                Cairo::RefPtr<Cairo::Context> c =
get_window()->create_cairo_context();
                Gtk::Allocation allocation = get_allocation();
                c->scale(allocation.get_width(),
allocation.get_height());
                const double font_size = 0.05;
                c->move_to(0, font_size);
                c->set_font_size(font_size);
                c->show_text("No Crash Here");
                return true;
        }
};

int main(int argc, char *argv[])
{
        Gtk::Main kit(argc, argv);
        Gtk::Window window;
        CairoDrawer cairo_drawer;
        cairo_drawer.show();
        window.add(cairo_drawer);
        kit.run(window);
}


-- 
Jonner