Controlling the Volume Widget

Example

The greenphone provides an example where the device uses /dev/mixer to modify the master volume control of the soundcard. By registering itself with the Audio Volume Manager to gain control of volume hardware keys, it can display a volume widget to reflect this specific volume. The Audio Volume Manager writes this value into a QValueSpaceItem and the volume widget is updated accordingly.

Heres the header file for reference.

    class GreenphoneVolumeService : public QtopiaIpcAdaptor
    {
        Q_OBJECT
        enum AdjustType { Relative, Absolute };

    public:
        GreenphoneVolumeService();
        ~GreenphoneVolumeService();

    public slots:
        void increaseVolume(int increment);
        void decreaseVolume(int decrement);
        void setMute(bool mute);

    private slots:
        void registerService();
        void setCallDomain();

    private:
        void adjustVolume(int leftChannel, int rightChannel, AdjustType);

        int m_leftChannelVolume;
        int m_rightChannelVolume;

        GreenphoneVolumeServicePrivate *m_d;
    };

Important to note is that the relevant public slot functions correspond to QCop messages that are invoked by the Audio Volume Manager.

The registration:

    void GreenphoneVolumeService::registerService()
    {
        QtopiaIpcEnvelope   e("QPE/AudioVolumeManager", "registerHandler(QString,QString)");

        e << QString("Headset") << QString("QPE/AudioVolumeManager/GreenphoneVolumeService");

        QTimer::singleShot(0, this, SLOT(setCallDomain()));
    }

A similar QCop message should be used to unregister.

Taking a look at the implementation of the increaseVolume() function, we let the Audio Volume Manager know of the changed volume.

    void GreenphoneVolumeService::increaseVolume(int increment)
    {
        adjustVolume(increment, increment, Relative);
        m_d->sendCurrentVolume();
    }

Shown below is an implementation to report the modified volume back to the Audio Volume Manager.

    void sendCurrentVolume()
    {
            QString volume;
            volume.setNum(currVolume);
            QtopiaIpcEnvelope e("QPE/AudioVolumeManager","currentVolume(QString)");
            e << volume;
    }

Please see: $QTOPIA_DEPO_PATH/src/server/media/volumemanagement/audiovolumemanager.{h,cpp}. Note: returned volume values should be in the range 0-100.

server/media/genericvolumeservice is a generic implementation that uses QAudioMixer for the audio system adjustment. This is used by qvfb and could be used for a device by adding server/media/genericvolumeservice to the devices project.pri file. The c3200 device profile has been changed to use this.

Sometimes with alsa the auto-detect for the master volume can be incorrect. To override the auto-detect for the master volume control element and force use of a particular element set $HOME/Settings/Trolltech/Sound.conf [System] MasterName="PCM" MasterControl set to true allows the service to save and restore MasterVolume. If MasterControl is false (default) then current volume is used instead and volume is not saved to config.

See also QtopiaIpcAdaptor and QValueSpaceItem.