[Ardour-Dev] ARDOUR::AutomationList and the StateChanged signal

[John Emmas]

Hi Paul.  I eventually found the problem.  'AudioRegion::_fade_in' wasn't
going out of scope but its 'events' list was becoming temporarily
invalidated.  The crash was happening because in function
AudioRegion::reset_fade_in_shape(), this call was being made:-

reset_fade_in_shape_width ((nframes_t)
                     audio_region()->fade_in().back()->when);

when 'audio_region()->fade_in()' has no elements.  Here's some code that
will illustrate the problem:-

void
AudioRegionView::reset_fade_in_shape ()
{
#if 1 // JE - For testing !!!
Curve& fadein = audio_region()->fade_in();
if (fadein.empty())
      cout << "NO FADE_IN ELEMENTS - CRASH SHOULD BE IMMINENT !!" << endl;
else
{
      size_t fs = fadein.size();
      cout << "Detected " << fs << " fade_in events" << endl;
}

// And this is the line that should crash if '_fade_in' has no elements
reset_fade_in_shape_width ((nframes_t) fadein.back()->when);

#else
// This is the original code
      reset_fade_in_shape_width ((nframes_t)
                   audio_region()->fade_in().back()->when);
#endif
}

The line after #else is the original code.  The lines above it are the same
code, broken down into steps and tested.  Run Ardour from the command
line and load a very simple session (say with just one timeline region).
You'll probably notice that its fade_in contains two events.  Now drag the
region slightly and try to undo the drag.  You should see that
'AudioRegionView::reset_fade_in_shape()' is getting called twice when the
fade_in has zero elements.  For some reason (probably luck) this doesn't
seem to cause any problems for gcc but it crashes when compiled using VC++.

I'm guessing that this would offer the simplest solution:-

void
AudioRegionView::reset_fade_in_shape ()
{
     if ( ! audio_region()->fade_in().empty() )
            reset_fade_in_shape_width ((nframes_t)
                         audio_region()->fade_in().back()->when);
}

Hopefully without any side-effects?

John