- Qt 5.5
- Qt Multimedia
- Spectrum Example
- waveform.h Example File
- Qt 5.5.1 Reference Documentation

# waveform.h Example File

spectrum/app/waveform.h

    /****************************************************************************
    **
    ** Copyright (C) 2015 The Qt Company Ltd.
    ** Contact: http://www.qt.io/licensing/
    **
    ** This file is part of the examples of the Qt Toolkit.
    **
    ** $QT_BEGIN_LICENSE:BSD$
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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