Render the mixer levels in a dB FS scale (#2672)

* Render the mixer levels in a dB FS scale

Adds the option to render the mixer levels in dB FS. By default this
option is disabled so that classes which inherit from Fader are not
affected by this change. However, in the code of the FxMixerView this
feature is enabled so that the mixer shows the levels in dB FS.

The ability to render in dB FS is exported as a property so that it can
also be set in a style sheet (not used as of now). The new property is
called "levelsDisplayedInDBFS".

There are now setters and getters for the min and max level.

Showing the levels in dB FS (which is a logarithmic scale) gives a less
"fidgety" impression when the levels are moving.

* Introduction of an init method in Fader

An init method was added to unify the initialization of the two Fader
constructors.

src/gui/FxMixerView.cpp

@@ -50,6 +50,7 @@
 #include "InstrumentTrack.h"
 #include "Song.h"
 #include "BBTrackContainer.h"
+#include "lmms_math.h"
 
 FxMixerView::FxMixerView() :
 	QWidget(),
@@ -280,6 +281,11 @@ FxMixerView::FxChannelView::FxChannelView(QWidget * _parent, FxMixerView * _mv,
 
 	m_fader = new Fader( &fxChannel->m_volumeModel,
 					tr( "FX Fader %1" ).arg( channelIndex ), m_fxLine );
+	m_fader->setLevelsDisplayedInDBFS();
+	// TODO dbvToAmp is really dBFSToAmp. Rename in later commit.
+	m_fader->setMinPeak(dbvToAmp(-40));
+	m_fader->setMaxPeak(dbvToAmp(12));
+
 	m_fader->move( 16-m_fader->width()/2,
 					m_fxLine->height()-
 					m_fader->height()-5 );

src/gui/widgets/Fader.cpp

@@ -57,6 +57,7 @@
 #include "ConfigManager.h"
 #include "TextFloat.h"
 #include "MainWindow.h"
+#include "lmms_math.h"
 
 
 TextFloat * Fader::s_textFloat = NULL;
@@ -74,6 +75,7 @@ Fader::Fader( FloatModel * _model, const QString & _name, QWidget * _parent ) :
 	m_fMinPeak( 0.01f ),
 	m_fMaxPeak( 1.1 ),
 	m_displayConversion( true ),
+	m_levelsDisplayedInDBFS(false),
 	m_moveStartPoint( -1 ),
 	m_startValue( 0 ),
 	m_peakGreen( 0, 0, 0 ),
@@ -100,13 +102,7 @@ Fader::Fader( FloatModel * _model, const QString & _name, QWidget * _parent ) :
 	m_leds = s_leds;
 	m_knob = s_knob;
 
-	setWindowTitle( _name );
-	setAttribute( Qt::WA_OpaquePaintEvent, false );
-	setMinimumSize( 23, 116 );
-	setMaximumSize( 23, 116);
-	resize( 23, 116 );
-	setModel( _model );
-	setHintText( "Volume:","%");
+	init(_model, _name);
 }
 
 
@@ -120,6 +116,7 @@ Fader::Fader( FloatModel * model, const QString & name, QWidget * parent, QPixma
 	m_fMinPeak( 0.01f ),
 	m_fMaxPeak( 1.1 ),
 	m_displayConversion( false ),
+	m_levelsDisplayedInDBFS(false),
 	m_moveStartPoint( -1 ),
 	m_startValue( 0 ),
 	m_peakGreen( 0, 0, 0 ),
@@ -134,13 +131,7 @@ Fader::Fader( FloatModel * model, const QString & name, QWidget * parent, QPixma
 	m_leds = leds;
 	m_knob = knob;
 
-	setWindowTitle( name );
-	setAttribute( Qt::WA_OpaquePaintEvent, false );
-	setMinimumSize( m_back->width(), m_back->height() );
-	setMaximumSize( m_back->width(), m_back->height() );
-	resize( m_back->width(), m_back->height() );
-	setModel( model );
-	setHintText( "Volume:","%");
+	init(model, name);
 }
 
 
@@ -149,6 +140,18 @@ Fader::~Fader()
 }
 
 
+void Fader::init(FloatModel * model, QString const & name)
+{
+	setWindowTitle( name );
+	setAttribute( Qt::WA_OpaquePaintEvent, false );
+	QSize backgroundSize = m_back->size();
+	setMinimumSize( backgroundSize );
+	setMaximumSize( backgroundSize );
+	resize( backgroundSize );
+	setModel( model );
+	setHintText( "Volume:","%");
+}
+
 
 
 void Fader::contextMenuEvent( QContextMenuEvent * _ev )
@@ -337,20 +340,81 @@ inline int Fader::calculateDisplayPeak( float fPeak )
 	return qMin( peak, m_back->height() );
 }
 
+
 void Fader::paintEvent( QPaintEvent * ev)
 {
 	QPainter painter(this);
 
-	// background
+	// Draw the background
 	painter.drawPixmap( ev->rect(), *m_back, ev->rect() );
 
+	// Draw the levels with peaks
+	if (getLevelsDisplayedInDBFS())
+	{
+		paintDBFSLevels(ev, painter);
+	}
+	else
+	{
+		paintLinearLevels(ev, painter);
+	}
+
+	// Draw the knob
+	painter.drawPixmap( 0, knobPosY() - m_knob->height(), *m_knob );
+}
+
+void Fader::paintDBFSLevels(QPaintEvent * ev, QPainter & painter)
+{
+	int height = m_back->height();
+	int width = m_back->width() / 2;
+	int center = m_back->width() - width;
+
+	float const maxDB(ampToDbv(m_fMaxPeak));
+	float const minDB(ampToDbv(m_fMinPeak));
+
+	// We will need to divide by the span between min and max several times. It's more
+	// efficient to calculate the reciprocal once and then to multiply.
+	float const fullSpanReciprocal = 1 / (maxDB - minDB);
+
+
+	// Draw left levels
+	float const leftSpan = ampToDbv(m_fPeakValue_L) - minDB;
+	int peak_L = height * leftSpan * fullSpanReciprocal;
+	QRect drawRectL( 0, height - peak_L, width, peak_L ); // Source and target are identical
+	painter.drawPixmap( drawRectL, *m_leds, drawRectL );
+
+	float const persistentLeftPeakDBFS = ampToDbv(m_persistentPeak_L);
+	int persistentPeak_L = height * (1 - (persistentLeftPeakDBFS - minDB) * fullSpanReciprocal);
+	if( persistentLeftPeakDBFS > minDB )
+	{
+		QColor const & peakColor = clips(m_persistentPeak_L) ? peakRed() : peakGreen();
+		painter.fillRect( QRect( 2, persistentPeak_L, 7, 1 ), peakColor );
+	}
+
+
+	// Draw right levels
+	float const rightSpan = ampToDbv(m_fPeakValue_R) - minDB;
+	int peak_R = height * rightSpan * fullSpanReciprocal;
+	QRect const drawRectR( center, height - peak_R, width, peak_R ); // Source and target are identical
+	painter.drawPixmap( drawRectR, *m_leds, drawRectR );
+
+	float const persistentRightPeakDBFS = ampToDbv(m_persistentPeak_R);
+	int persistentPeak_R = height * (1 - (persistentRightPeakDBFS - minDB) * fullSpanReciprocal);
+	if( persistentRightPeakDBFS > minDB )
+	{
+		QColor const & peakColor = clips(m_persistentPeak_R) ? peakRed() : peakGreen();
+		painter.fillRect( QRect( 14, persistentPeak_R, 7, 1 ), peakColor );
+	}
+}
+
+void Fader::paintLinearLevels(QPaintEvent * ev, QPainter & painter)
+{
 	// peak leds
 	//float fRange = abs( m_fMaxPeak ) + abs( m_fMinPeak );
 
 	int height = m_back->height();
 	int width = m_back->width() / 2;
 	int center = m_back->width() - width;
-	
+
 	int peak_L = calculateDisplayPeak( m_fPeakValue_L - m_fMinPeak );
 	int persistentPeak_L = qMax<int>( 3, calculateDisplayPeak( m_persistentPeak_L - m_fMinPeak ) );
 	painter.drawPixmap( QRect( 0, peak_L, width, height - peak_L ), *m_leds, QRect( 0, peak_L, width, height - peak_L ) );
@@ -372,18 +436,15 @@ void Fader::paintEvent( QPaintEvent * ev)
 			? peakGreen()
 			: peakRed() );
 	}
-
-	// knob
-	painter.drawPixmap( 0, knobPosY() - m_knob->height(), *m_knob );
 }
 
 
-QColor Fader::peakGreen() const
+QColor const & Fader::peakGreen() const
 {
 	return m_peakGreen;
 }
 
-QColor Fader::peakRed() const
+QColor const & Fader::peakRed() const
 {
 	return m_peakRed;
 }