Responsive "Effects chain" & "User controller" LEDs

[Sawuare]

• Turn off the effects chain LED when its chain is empty.
• Turn on the user controller LED when a controller is selected.

Also, removed an unused function: setEnabled()

Closes #3620.

[PhysSong]

Since EffectChain::clear already have the same functionality, I think you can implement this in EffectChain::removeEffect instead.

[Sawuare]

Done in d3e65ca

[Wallacoloo]

Using (or even having) a dataUnchanged() signal on a model smells a bit fishy. LMMS mostly uses a model-view-controller-like paradigm (MVC), and usually the model emits signals to notify the views that the model's changed.

But in this case, the dataUnchanged() signal is being used to notify the view that the controller attempted to do something - not that the model has been updated. If we wanted to hook into something the controller's doing (I think LMMS mostly merges the controller role into the view), the signal should be placed right at the source - on the controller.

I don't think I'm capable of giving a more coherent explanation of why I think dataUnchanged() is a bad thing to have or use, but it feels like a leaky abstraction - like we're losing the main advantage of MVC in that the model and view are no longer decoupled. If you can see a way to achieve this work without using dataUnchanged, I'd recommend that. I'm unfortunately not familiar enough with LMMS to present such a solution (and if you don't see a better way of doing it, that's okay - I'm still happy to see you implement this feature & I'm not going to hold up the PR over something like that).

[PhysSong]

Something more about dataUnchanged... We have two use cases: one in BBTrackContainer's constructor, and the other in Song's constructor. However, I guess they doesn't do anything. What I can see about BBTrackContainer is 00d2d4a, but I don't know why we still have this.

Using (or even having) a dataUnchanged() signal on a model smells a bit fishy.

I think the intention was notify that user interacted with a controller when the value isn't changed(ex. select current item in combo box). However, I think we can cover such cases on controller's side(ComboBox in this case).

If you can see a way to achieve this work without using dataUnchanged, I'd recommend that.

and if you don't see a better way of doing it, that's okay

I think so. 👍

[Sawuare]

Thanks for your input, @Wallacoloo and @PhysSong.

I think the intention was notify that user interacted with a controller when the value isn't changed(ex. select current item in combo box).

Exactly. I don't know a way to achieve this without using dataUnchanged().