Qt 5.7 | Qt Multimedia | Spectrum Example | levelmeter.cpp Example File

Qt 5.7.1 Reference Documentation

# levelmeter.cpp Example File

multimedia/spectrum/app/levelmeter.cpp

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      #include "levelmeter.h"

      #include <math.h>

      #include <QPainter>
      #include <QTimer>
      #include <QDebug>

      // Constants
      const int RedrawInterval = 100; // ms
      const qreal PeakDecayRate = 0.001;
      const int PeakHoldLevelDuration = 2000; // ms

      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)
      {
          // Smooth the RMS signal
          const qreal smooth = pow(qreal(0.9), static_cast<qreal>(numSamples) / 256); // TODO: remove this magic number
          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()
      {
          // Decay the peak signal
          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;

          // Check whether to clear the peak hold level
          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);
      }