waveform.h Example File

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  #ifndef WAVEFORM_H
  #define WAVEFORM_H

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

  /**
   * 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:
      explicit Waveform(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 bufferChanged(qint64 position, qint64 length, const QByteArray &buffer);
      void audioPositionChanged(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:
      qint64                  m_bufferPosition;
      qint64                  m_bufferLength;
      QByteArray              m_buffer;

      qint64                  m_audioPosition;
      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