Fix "party stoppers" in Master Sync

[RJ Skerry-Ryan]

Here's a list of party-stoppers in the master sync support:

* Deck passthrough activates
* Track ejected
* Beatgrid on track cleared or becomes empty (0BPM)
* Vinyl control activated on follower (when master is already VC enabled)
* Rogue script sets 'master' and 'pfl' to 0.

We should gracefully hand-off from master or do something reasonable when these things happen.

[Owen Williams (ywwg)]

If the user has passthrough active, and then they try to enable sync mode, should we:
1. disable passthrough, or
2. disallow the enable change?

When vinyl control is active, we disable vinyl control -- this makes sense because we're handing off from vinyl control to sync control. But for passthrough, disabling passthrough would cause a complete change in audio processing. So for now I'm picking 2 and disabling enabling passthrough.

As a protection, if somehow the user forces sync on, I will still disable passthrough. But the idea is to head it off at the pass in synccontrol::slotSyncModeChangeRequest

[Owen Williams (ywwg)]

What do you mean by master and pfl being set to 0?

[Owen Williams (ywwg)]

* Deck passthrough activates -> sync disables
* Track ejected -> if master, sync disables, otherwise no change.
* Beatgrid on track cleared or becomes empty (0BPM) -> if quantize enabled, disable it (that's all we can do from bpmcontrol)
* Vinyl control activated on follower (when master is already VC enabled) -> disable sync
* Rogue script sets 'master' and 'pfl' to 0. -> don't understand this one.

pull request: https://github.com/mixxxdj/mixxx/pull/128

[Owen Williams (ywwg)]

See my question about rogue scripts

[Owen Williams (ywwg)]

depends on:
https://bugs.launchpad.net/mixxx/+bug/1286843
https://bugs.launchpad.net/mixxx/+bug/1286848
https://bugs.launchpad.net/mixxx/+bug/1285450

[Owen Williams (ywwg)]

For now I'm marking this fixed, because as a meta-bug this hasn't been really helpful. Individual party-stopper bugs should be filed separately.

[Swiftb0y (swiftb0y)]

Mixxx now uses GitHub for bug tracking. This bug has been migrated to:
https://github.com/mixxxdj/mixxx/issues/7227