waveform.h Example File

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 #ifndef WAVEFORM_H
 #define WAVEFORM_H

 #include <QWidget>
 #include <QtMultimedia/QAudioFormat>
 #include <QPixmap>
 #include <QScopedPointer>

 QT_FORWARD_DECLARE_CLASS(QByteArray)

 /**
  * Widget which displays a section of the audio waveform.
  *
  * The waveform is rendered on a set of QPixmaps which form a group of tiles
  * whose extent covers the widget.  As the audio position is updated, these
  * tiles are scrolled from left to right; when the left-most tile scrolls
  * outside the widget, it is moved to the right end of the tile array and
  * painted with the next section of the waveform.
  */
 class Waveform : public QWidget {
     Q_OBJECT
 public:
     Waveform(const QByteArray &buffer, QWidget *parent = 0);
     ~Waveform();

     // QWidget
     void paintEvent(QPaintEvent *event);
     void resizeEvent(QResizeEvent *event);

     void initialize(const QAudioFormat &format, qint64 audioBufferSize, qint64 windowDurationUs);
     void reset();

     void setAutoUpdatePosition(bool enabled);

 public slots:
     void dataLengthChanged(qint64 length);
     void positionChanged(qint64 position);

 private:
     static const int NullIndex = -1;

     void deletePixmaps();

     /*
      * (Re)create all pixmaps, repaint and update the display.
      * Triggers an update();
      */
     void createPixmaps(const QSize &newSize);

     /*
      * Update window position.
      * Triggers an update().
      */
     void setWindowPosition(qint64 position);

     /*
      * Base position of tile
      */
     qint64 tilePosition(int index) const;

     /*
      * Structure which identifies a point within a given
      * tile.
      */
     struct TilePoint
     {
         TilePoint(int idx = 0, qint64 pos = 0, qint64 pix = 0)
         :   index(idx), positionOffset(pos), pixelOffset(pix)
         { }

         // Index of tile
         int     index;

         // Number of bytes from start of tile
         qint64  positionOffset;

         // Number of pixels from left of corresponding pixmap
         int     pixelOffset;
     };

     /*
      * Convert position in m_buffer into a tile index and an offset in pixels
      * into the corresponding pixmap.
      *
      * \param position  Offset into m_buffer, in bytes

      * If position is outside the tile array, index is NullIndex and
      * offset is zero.
      */
     TilePoint tilePoint(qint64 position) const;

     /*
      * Convert offset in bytes into a tile into an offset in pixels
      * within that tile.
      */
     int tilePixelOffset(qint64 positionOffset) const;

     /*
      * Convert offset in bytes into the window into an offset in pixels
      * within the widget rect().
      */
     int windowPixelOffset(qint64 positionOffset) const;

     /*
      * Paint all tiles which can be painted.
      * \return true iff update() was called
      */
     bool paintTiles();

     /*
      * Paint the specified tile
      *
      * \pre Sufficient data is available to completely paint the tile, i.e.
      *      m_dataLength is greater than the upper bound of the tile.
      */
     void paintTile(int index);

     /*
      * Move the first n tiles to the end of the array, and mark them as not
      * painted.
      */
     void shuffleTiles(int n);

     /*
      * Reset tile array
      */
     void resetTiles(qint64 newStartPos);

 private:
     const QByteArray&       m_buffer;
     qint64                  m_dataLength;
     qint64                  m_position;
     QAudioFormat            m_format;

     bool                    m_active;

     QSize                   m_pixmapSize;
     QVector<QPixmap*>       m_pixmaps;

     struct Tile {
         // Pointer into parent m_pixmaps array
         QPixmap*            pixmap;

         // Flag indicating whether this tile has been painted
         bool                painted;
     };

     QVector<Tile>           m_tiles;

     // Length of audio data in bytes depicted by each tile
     qint64                  m_tileLength;

     // Position in bytes of the first tile, relative to m_buffer
     qint64                  m_tileArrayStart;

     qint64                  m_windowPosition;
     qint64                  m_windowLength;

 };

 #endif // WAVEFORM_H