[Deere] Performance fix - Switch from SVG to PNG for VuMeters , tweak <PeakHoldTime> value

[esbrandt]

Follow-up to #1573

I found this super hot with my old Macbook Pro 2011 with integrated Intel HD Graphics 3000, eats 12% of CPU time.

mixxx/src/widget/paintable.cpp

Lines 242 to 252 in 5fc314e

	// NOTE(rryan): QSvgRenderer render does not clip for us -- it
	// applies a world transformation using viewBox and renders the
	// entire SVG to the painter. We save/restore the QPainter in case
	// there is an existing clip region (I don't know of any Mixxx code
	// that uses one but we may in the future).
	pPainter->save();
	pPainter->setClipping(true);
	pPainter->setClipRect(targetRect);
	m_pSvg->setViewBox(sourceRect);
	m_pSvg->render(pPainter, targetRect);
	pPainter->restore();

m_pSvg->render(pPainter, targetRect); was updated over 90/sec

CPU Utilization

.	2-deck	2-deck (Spinny)	4-Deck	4-Deck (Spinny)
SVG PeakHoldTime 1000	70 %	75%	86%	111%
PNG PeakHoldTime 1000	58 %	66 %	82%	106%
PNG PeakHoldTime 300	50 %	60 %	75%	105%

Deere, 0 samplers, 0 effects, 0 controllers, Default GLSL Waveform@30fps 20% zoom, RGB overview, Keylock active (Rubberband) , Parallel waveform

Conclusion:

• Switching from SVG to PNG for vumeters makes a differences, as well as lowering the vumeter´s peakholdtime
• Playing with 4 decks is practical impossible, as the UI often lags/drops out when interacting.

[Be-ing]

LGTM thanks. Should we lower the peak hold times for other skins too?

[daschuer]

What is the theory behind the peak hold time CPU drain?