levelmeter.cpp Example File
demos/spectrum/app/levelmeter.cpp
 
 
 #include "levelmeter.h"
 #include <math.h>
 #include <QPainter>
 #include <QTimer>
 #include <QDebug>
 
 const int RedrawInterval = 100; 
 const qreal PeakDecayRate = 0.001;
 const int PeakHoldLevelDuration = 2000; 
 LevelMeter::LevelMeter(QWidget *parent)
     :   QWidget(parent)
     ,   m_rmsLevel(0.0)
     ,   m_peakLevel(0.0)
     ,   m_decayedPeakLevel(0.0)
     ,   m_peakDecayRate(PeakDecayRate)
     ,   m_peakHoldLevel(0.0)
     ,   m_redrawTimer(new QTimer(this))
     ,   m_rmsColor(Qt::red)
     ,   m_peakColor(255, 200, 200, 255)
 {
     setSizePolicy(QSizePolicy::Fixed, QSizePolicy::Preferred);
     setMinimumWidth(30);
     connect(m_redrawTimer, SIGNAL(timeout()), this, SLOT(redrawTimerExpired()));
     m_redrawTimer->start(RedrawInterval);
 }
 LevelMeter::~LevelMeter()
 {
 }
 void LevelMeter::reset()
 {
     m_rmsLevel = 0.0;
     m_peakLevel = 0.0;
     update();
 }
 void LevelMeter::levelChanged(qreal rmsLevel, qreal peakLevel, int numSamples)
 {
     
     const qreal smooth = pow(qreal(0.9), static_cast<qreal>(numSamples) / 256); 
     m_rmsLevel = (m_rmsLevel * smooth) + (rmsLevel * (1.0 - smooth));
     if (peakLevel > m_decayedPeakLevel) {
         m_peakLevel = peakLevel;
         m_decayedPeakLevel = peakLevel;
         m_peakLevelChanged.start();
     }
     if (peakLevel > m_peakHoldLevel) {
         m_peakHoldLevel = peakLevel;
         m_peakHoldLevelChanged.start();
     }
     update();
 }
 void LevelMeter::redrawTimerExpired()
 {
     
     const int elapsedMs = m_peakLevelChanged.elapsed();
     const qreal decayAmount = m_peakDecayRate * elapsedMs;
     if (decayAmount < m_peakLevel)
         m_decayedPeakLevel = m_peakLevel - decayAmount;
     else
         m_decayedPeakLevel = 0.0;
     
     if (m_peakHoldLevelChanged.elapsed() > PeakHoldLevelDuration)
         m_peakHoldLevel = 0.0;
     update();
 }
 void LevelMeter::paintEvent(QPaintEvent *event)
 {
     Q_UNUSED(event)
     QPainter painter(this);
     painter.fillRect(rect(), Qt::black);
     QRect bar = rect();
     bar.setTop(rect().top() + (1.0 - m_peakHoldLevel) * rect().height());
     bar.setBottom(bar.top() + 5);
     painter.fillRect(bar, m_rmsColor);
     bar.setBottom(rect().bottom());
     bar.setTop(rect().top() + (1.0 - m_decayedPeakLevel) * rect().height());
     painter.fillRect(bar, m_peakColor);
     bar.setTop(rect().top() + (1.0 - m_rmsLevel) * rect().height());
     painter.fillRect(bar, m_rmsColor);
 }