levelmeter.h Example File

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 #ifndef LEVELMETER_H
 #define LEVELMETER_H

 #include <QTime>
 #include <QWidget>

 /**
  * Widget which displays a vertical audio level meter, indicating the
  * RMS and peak levels of the window of audio samples most recently analyzed
  * by the Engine.
  */
 class LevelMeter : public QWidget
 {
     Q_OBJECT

 public:
     explicit LevelMeter(QWidget *parent = 0);
     ~LevelMeter();

     void paintEvent(QPaintEvent *event) override;

 public slots:
     void reset();
     void levelChanged(qreal rmsLevel, qreal peakLevel, int numSamples);

 private slots:
     void redrawTimerExpired();

 private:
     /**
      * Height of RMS level bar.
      * Range 0.0 - 1.0.
      */
     qreal m_rmsLevel;

     /**
      * Most recent peak level.
      * Range 0.0 - 1.0.
      */
     qreal m_peakLevel;

     /**
      * Height of peak level bar.
      * This is calculated by decaying m_peakLevel depending on the
      * elapsed time since m_peakLevelChanged, and the value of m_decayRate.
      */
     qreal m_decayedPeakLevel;

     /**
      * Time at which m_peakLevel was last changed.
      */
     QTime m_peakLevelChanged;

     /**
      * Rate at which peak level bar decays.
      * Expressed in level units / millisecond.
      */
     qreal m_peakDecayRate;

     /**
      * High watermark of peak level.
      * Range 0.0 - 1.0.
      */
     qreal m_peakHoldLevel;

     /**
      * Time at which m_peakHoldLevel was last changed.
      */
     QTime m_peakHoldLevelChanged;

     QTimer *m_redrawTimer;

     QColor m_rmsColor;
     QColor m_peakColor;

 };

 #endif // LEVELMETER_H