[cairo] Error: Target surface has been finished

[Evan White]

This is my first post to a mailing list ever.  I am not a heavy 
programmer I have only had two C++ courses in college.  I am in my 
senior year working on my engineering design project where my group is 
building a replacement for your vehicle's instrument cluster.

I have been able to draw to a window three gauges, but when I try to 
simulate the interface receiving data from our hardware with a text file 
I get the following error:

--------
glibmm-ERROR **:
unhandled exception (type std::exception) in signal handler:
what: the target surface has been finished

aborting...
Aborted
--------

Using a couple of cout statements I was able to figure out that I get 
this error when I am calling the stroke() function when I am recalling 
my drawing functions through my signal_io callback.  Does anyone know 
how I could fix this problem and what does this error means.

Here is some of my code I think that might help.

bool Default::on_expose_event(GdkEventExpose* event) {
   Glib::RefPtr<Gdk::Window> window = get_window();
   if(window) {
       Gtk::Allocation allocation = get_allocation();
       totalDrawableWidth = allocation.get_width();
       totalDrawableHeight = allocation.get_height();
             cr = window->create_cairo_context();          
cr->rectangle(event->area.x, event->area.y, event->area.width, 
event->area.height);
       cr->clip();
             // Draw initial gauges
       drawGauge(gaugePadding*totalDrawableWidth);  // Speed Gauge
       drawGauge((gaugeWidth + gaugePadding)*totalDrawableWidth);  // 
RPM Gauge
             drawNeedle(0, gaugePadding*totalDrawableWidth);  // Speed 
Needle
       drawNeedle(0, (gaugeWidth + gaugePadding)*totalDrawableWidth);  
// RPM Needle
             drawFuelGauge(0);
             // start animating the screen
       file_read = Glib::IOChannel::create_from_file("test.txt","r");
       Glib::signal_io().connect(sigc::mem_fun(*this, &Default::Update), 
file_read, Glib::IO_IN | Glib::IO_HUP);
   }
}

bool Default::Update(Glib::IOCondition io_condition) {
     if ((io_condition & Glib::IO_IN) == 0) {
       cerr << "Invalid fifo response" << std::endl;
   }
   else {
       Glib::ustring buf;
       #ifdef GLIBMM_EXCEPTIONS_ENABLED
       file_read->read_line(buf);
       #else
       auto_ptr<Glib::Error> ex;
       file_read->read_line(buf, ex);
       if(ex.get()) {
           cout << "ouch\n";
           cerr << "Error: " << ex->what() << endl;
       }
       #endif //GLIBMM_EXCEPTIONS_ENABLED

       string temp = buf.raw();
       string tempVal = temp.substr(2, temp.length()-1);
       temp.erase(1, temp.length()-1);
       int SensID = atoi(temp.c_str());
       double value = atof(tempVal.c_str());
       switch(SensID) {
           case 0:
                   cout << "speed baby\n";
               processSpeed(value);
               break;
           case 1:
               processRPM(value);
               break;
           case 2:
               processFuel(value);
               break;
           default:
               break;
       }      }
   return true;
}

void Default::drawGauge(double Offset) {
   cout << "In gauge\n";
   cr->set_source_rgb(0,0,0);
   cr->set_line_width(5);
   cr->set_line_join(Cairo::LINE_JOIN_ROUND);
     //draw gauge outlines
   cr->save();
   cout << "drawing gauge\n";
   cr->arc(gaugeRadius * totalDrawableWidth + Offset + 1, 
totalDrawableHeight - (gaugePadding * totalDrawableHeight), gaugeRadius 
* totalDrawableWidth, M_PI, 0);
   cout << "stroking arc\n";
   cr->stroke();    // <- PROBLEM OCCURRS WHEN I GET TO THIS LINE
   cout << "done\n";
   cr->restore();
}