Re: [Loopdub-devel] Synchronizing MIDI controls with LoopDub

[Stephen S. <rad...@gm...>]

Hi,

I'm afraid I don't have time to give you a point-for-point answer
right now.  I've thought about it a bit, but in fact I think a lot
better about these things in C++ rather than in english, so I started
coding a little to see what issues might arise.

I have to thank you for making me take a critical eye to the midi
code, I haven't looked at it in a while.  I was horrified to find that
the control codes are indexed by slider rather than the other way
around..  It means each CC message received is passed through a whole
series of if/else clauses-- ugly!

Thinking about my suggestion for how to do it, I created a class to
represent MIDI values.  Each one is assigned to a control code when
the configuration file is loaded, and each one has access to a GUI
slider.  (I had to create some base classes for the GUI sliders and
buttons to abstract the Set/GetValue functionality, which I think is
probably a good idea anyways..)

There are two Set functions for the MidiValue class, one is SetValue()
which is equivalent to your "internal" CtrlSource enum, and the other
is ReceiveCC() which is equivalent to "midi" CtrlSource.  Depending on
which of these functions is called it will set the state of the
MidiValue as NEEDSYNC or PICKUP.

Anyways, this can be found in the "feature/midisync" branch in git.
It's not at all complete, but should give you some idea of what I'm
talking about.

I'm not at all sure this is better or worse than what you suggest..
perhaps the LoobOb is afterall the right place for this stuff.
However I think it's definitely a good idea to reduce the processing
that occurs whenever a CC message is received, and indexing the
sliders by control code is probably necessary, so I'm glad I had a
hack at it.

I would be interested to know what you think, and how it differs from
your approach.

There are only two points in your message that I think I disagree
with.  First is the necessity of handling this corner case where the
user unplugs a MIDI cable and reattaches it.  I have little interest
in handing that case -- if the user is doing such a thing, he'll
expect things to go strange, and a key command 's' to re-synchronize
manually is probably sufficient, as we have now.

Secondly,

> 2. When we receive a CC message, if is exactly one tick away from the
> current internal value, then we update the value. If it is not, then
> we know that the MIDI slider and the internal slider have drifted
> apart, and the user needs to get them back into sync before we will
> respond to their CC messages.

I think it is quite dangerous to assume that all CC messages will be
exactly 1 tick apart.  You mention yourself that it won't handle the
button case -- there may be other cases where the user wants to set
everything to a particular value.  (Loading a preset for example.)  My
idea for 'pick up' was to only enable that state when a sample is
loaded (i.e., the 'internal' case, a context change.)  It might also
be useful for when the user moves a slider, but again, this state is
deterministically available to the program and doesn't depend on the
difference between two successive CC values.


cheers,
Steve