refs #387, preparation for level meter

* not yet connected with audio

src/blackgui/levelmeter.h

@@ -0,0 +1,85 @@
+/* Copyright (C) 2013
+ * swift project Community / Contributors
+ *
+ * This file is part of swift project. It is subject to the license terms in the LICENSE file found in the top-level
+ * directory of this distribution and at http://www.swift-project.org/license.html. No part of swift project,
+ * including this file, may be copied, modified, propagated, or distributed except according to the terms
+ * contained in the LICENSE file.
+ *
+ * Class based on qt example: Copyright (C) 2012 Nokia Corporation and/or its subsidiary(-ies)
+ */
+
+//! \file
+
+#ifndef BLACKGUI_LEVELMETER_H
+#define BLACKGUI_LEVELMETER_H
+
+#include <QTime>
+#include <QWidget>
+
+namespace BlackGui
+{
+
+    /**
+     * 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 CLevelMeter : public QWidget
+    {
+        Q_OBJECT
+    public:
+        //! Constructor
+        CLevelMeter(QWidget *parent = 0);
+
+        //! Destructor
+        ~CLevelMeter();
+
+        //! \copydoc QWidget::paintEvent
+        void paintEvent(QPaintEvent *event) override;
+
+    public slots:
+
+        //! Clean up
+        void reset();
+
+        //! Values
+        void levelChanged(double rmsLevel, double peakLevel, int numSamples);
+
+    private slots:
+        void ps_redrawTimerExpired();
+
+    private:
+        const int RedrawInterval        = 100; // ms
+        const double PeakDecayRate      = 0.001;
+        const int PeakHoldLevelDuration = 2000; // ms
+
+        //! Height of RMS level bar, range 0.0 - 1.0.
+        double m_rmsLevel = 0.0;
+
+        //! Most recent peak level, range 0.0 - 1.0.
+        double m_peakLevel = 0.0;
+
+        //! 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.
+        double m_decayedPeakLevel = 0.0;
+
+        //! Time at which m_peakLevel was last changed.
+        QTime m_peakLevelChanged;
+
+        //! Rate at which peak level bar decays.  Expressed in level units / millisecond.
+        double m_peakDecayRate;
+
+        //! High watermark of peak level. Range 0.0 - 1.0.
+        double m_peakHoldLevel = 0.0;
+
+        //! Time at which m_peakHoldLevel was last changed.
+        QTime m_peakHoldLevelChanged;
+
+        QTimer *m_redrawTimer;
+        QColor m_rmsColor;
+        QColor m_peakColor;
+    };
+}
+
+#endif // guard