Qt Reference Documentation

# waveform.h Example File

demos/spectrum/app/waveform.h

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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(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