Knob arc tweaks

[ronso0]

This tweaks WKnobComposed arcs (#2275 ) to always draw knob arcs circularly regardless of the widget's aspect ratio.
I also added an optional background arc.

The arcs are now set up like this

<KnobComposed>
  <Size>35f,30f</Size>
  <Knob>skin:/knob.svg</Knob>
  <BackPath>skin:/knob_bg.svg</BackPath>
  <MinAngle>-135</MinAngle>
  <MaxAngle>135</MaxAngle>
  <ArcRadius>12.5</ArcRadius>
  <ArcUnipolar>true/false</ArcUnipolar> // default: false
  <ArcColor>#654321</ArcColor>
  <ArcBgColor>#000</ArcBgColor>
  <ArcThickness>2</ArcThickness>
  <ArcBgThickness>1.5</ArcBgThickness>
  <KnobCenterYOffset>2</KnobCenterYOffset>
  <Connection>
    <ConfigKey>group,control</ConfigKey>
  </Connection>
</KnobComposed>

ToDo

• remove demo styles

[ronso0]

We should also add a <ArcReverse> option later on to allow drawing arcs counter-clockwise. Effect parameters (and Meta knobs?) like LowPassFilter and Downsampling could use that to draw an arc that adequately reflects the actual effect on the signal.
@Be-ing Could WEffectParameterKnobComposed request that info from the effect manifest? Did you think about something like this when working on #2618 ?

[ronso0]

(marked as draft so we don't accidentally merge it with the demo implementation)

[Be-ing]

Interesting idea. We could add a bool to the EffectParameterManifest for that.

[ronso0]

@Holzhaus @zezic
Any comments from you?

[Holzhaus]

Looks super nice on your Screenshots already, but I didn't have time to test it myself yet.
I guess it's not possible to set the arc color via qss? That would make it possible to have different colors for different color schemes.

[ronso0]

Right now I'm about to tqeak LateNight which already has a nice template/variable system, and there the knob colors, radius etc. are set in the <Scheme> nodes via <SetVariable>. All color defs in one place, as easy as it gets...

[Holzhaus]

Beautiful, thank you! LGTM.

[ronso0]

Thanks! It's ready then.
Reminder for myself: add docu to the skin wiki

[Be-ing]

Are you planning to add this to LateNight for 2.3?

[ronso0]

Are you planning to add this to LateNight for 2.3?

Sure, that was basically the motivation for this and the slider bars.
Considering hot it did and will evolve, I think LateNight should be the default skin in 2.3.
sneak preview:

[Be-ing]

OOOOOOOO that looks niiiice!

[Be-ing]

I think the master, booth, and headphone gain knobs should not show arcs at center though

[ronso0]

Unlike relative +/- knobs (EQ, filter, headMix, balance), Master, Booth etc. are absolute level knobs after all (not the most descriptibe term) which have zero "effect" when fully turned ccw. Thus the level should be visible even though it's mostly stays at the default value in most use cases.

We can disccuss all that in detail in LateNight update PR.