Qt Reference Documentation

# levelmeter.h Example File

demos/spectrum/app/levelmeter.h

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

         void paintEvent(QPaintEvent *event);

     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