Extending The Effects Engine Report W4

Hello,

It was a busy week at university because I had my last exam on Friday and after that I had to pack my things and move back home. Thankfully, school is over and I can focus entirely on Mixxx from now on.

I talked with Daniel about the software design for switch type parameters. I proposed this[1] design and I thought that instead of creating a ControlEffectKnob in EffectParameterSlot we can create either a ControlPushButton or a ControlPotmeter, based on manifest's ControlHint. Unfortunately this is not possible, as my mentor pointed me out, because of two reasons:

 * The skin is setting all connections when it is loaded. It cannot connect to a ControlObject which will be created afterwards
 * The effect change is processed during the audio callback and we shouldn't use new() and delete() inside this function because they have an unpredictable execution time

So we settled for the design which uses two separate lists of EffectParameters: one for knobs and one for buttons (switch parameters). After fixing a couple of typos in my implementation it is now working and it is updating the EffectParameters accordingly.

I had to introduce a new field in EffectsRequest::MessageType enum (SET_PARAMETER_BUTTON_PARAMETERS) to be able to extract the EffectParameter from the corresponding QList (knobs or buttons) inside EngineEffect::processEffectsRequest(). However, it still has a problem. Even though it is correctly updating the values which are processed by the framework, it doesn't display the same values in the GUI.

I have resolved the master conflicts for the EQ Default branch[2]. It is now using memcpy and memset for copying and initializing buffers and coefficients. I have also commented out the RBGW Mix, because Daniel found some issues with the involved filters.

Cheers,
Nicu Badescu

[1]
[2] - https://github.com/mixxxdj/mixxx/pull/267/files

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