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Diffstat (limited to 'src/multimedia/audio/qaudio.cpp')
| -rw-r--r-- | src/multimedia/audio/qaudio.cpp | 154 |
1 files changed, 154 insertions, 0 deletions
diff --git a/src/multimedia/audio/qaudio.cpp b/src/multimedia/audio/qaudio.cpp index c708fa4f8..d4f89e898 100644 --- a/src/multimedia/audio/qaudio.cpp +++ b/src/multimedia/audio/qaudio.cpp @@ -39,16 +39,20 @@ #include <qaudio.h> +#include <qmath.h> #include <QDebug> QT_BEGIN_NAMESPACE +#define LOG100 4.60517018599 + static void qRegisterAudioMetaTypes() { qRegisterMetaType<QAudio::Error>(); qRegisterMetaType<QAudio::State>(); qRegisterMetaType<QAudio::Mode>(); qRegisterMetaType<QAudio::Role>(); + qRegisterMetaType<QAudio::VolumeScale>(); } Q_CONSTRUCTOR_FUNCTION(qRegisterAudioMetaTypes) @@ -111,6 +115,134 @@ Q_CONSTRUCTOR_FUNCTION(qRegisterAudioMetaTypes) \sa QMediaPlayer::setAudioRole() */ +/*! + \enum QAudio::VolumeScale + + This enum defines the different audio volume scales. + + \value LinearVolumeScale Linear scale. \c 0.0 (0%) is silence and \c 1.0 (100%) is full + volume. All Qt Multimedia classes that have an audio volume use + a linear scale. + \value CubicVolumeScale Cubic scale. \c 0.0 (0%) is silence and \c 1.0 (100%) is full + volume. + \value LogarithmicVolumeScale Logarithmic Scale. \c 0.0 (0%) is silence and \c 1.0 (100%) is + full volume. UI volume controls should usually use a logarithmic + scale. + \value DecibelVolumeScale Decibel (dB, amplitude) logarithmic scale. \c -200 is silence + and \c 0 is full volume. + + \since 5.8 + \sa QAudio::convertVolume() +*/ + +namespace QAudio +{ + +/*! + \fn qreal QAudio::convertVolume(qreal volume, VolumeScale from, VolumeScale to) + + Converts an audio \a volume \a from a volume scale \a to another, and returns the result. + + Depending on the context, different scales are used to represent audio volume. All Qt Multimedia + classes that have an audio volume use a linear scale, the reason is that the loudness of a + speaker is controlled by modulating its voltage on a linear scale. The human ear on the other + hand, perceives loudness in a logarithmic way. Using a logarithmic scale for volume controls + is therefore appropriate in most applications. The decibel scale is logarithmic by nature and + is commonly used to define sound levels, it is usually used for UI volume controls in + professional audio applications. The cubic scale is a computationally cheap approximation of a + logarithmic scale, it provides more control over lower volume levels. + + The following example shows how to convert the volume value from a slider control before passing + it to a QMediaPlayer. As a result, the perceived increase in volume is the same when increasing + the volume slider from 20 to 30 as it is from 50 to 60: + + \snippet multimedia-snippets/audio.cpp Volume conversion + + \since 5.8 + \sa VolumeScale, QMediaPlayer::setVolume(), QAudioOutput::setVolume(), + QAudioInput::setVolume(), QSoundEffect::setVolume(), QMediaRecorder::setVolume() +*/ +qreal convertVolume(qreal volume, VolumeScale from, VolumeScale to) +{ + switch (from) { + case LinearVolumeScale: + volume = qMax(qreal(0), volume); + switch (to) { + case LinearVolumeScale: + return volume; + case CubicVolumeScale: + return qPow(volume, qreal(1 / 3.0)); + case LogarithmicVolumeScale: + return 1 - std::exp(-volume * LOG100); + case DecibelVolumeScale: + if (volume < 0.001) + return qreal(-200); + else + return qreal(20.0) * std::log10(volume); + } + break; + case CubicVolumeScale: + volume = qMax(qreal(0), volume); + switch (to) { + case LinearVolumeScale: + return volume * volume * volume; + case CubicVolumeScale: + return volume; + case LogarithmicVolumeScale: + return 1 - std::exp(-volume * volume * volume * LOG100); + case DecibelVolumeScale: + if (volume < 0.001) + return qreal(-200); + else + return qreal(3.0 * 20.0) * std::log10(volume); + } + break; + case LogarithmicVolumeScale: + volume = qMax(qreal(0), volume); + switch (to) { + case LinearVolumeScale: + if (volume > 0.99) + return 1; + else + return -std::log(1 - volume) / LOG100; + case CubicVolumeScale: + if (volume > 0.99) + return 1; + else + return qPow(-std::log(1 - volume) / LOG100, qreal(1 / 3.0)); + case LogarithmicVolumeScale: + return volume; + case DecibelVolumeScale: + if (volume < 0.001) + return qreal(-200); + else if (volume > 0.99) + return 0; + else + return qreal(20.0) * std::log10(-std::log(1 - volume) / LOG100); + } + break; + case DecibelVolumeScale: + switch (to) { + case LinearVolumeScale: + return qPow(qreal(10.0), volume / qreal(20.0)); + case CubicVolumeScale: + return qPow(qreal(10.0), volume / qreal(3.0 * 20.0)); + case LogarithmicVolumeScale: + if (qFuzzyIsNull(volume)) + return 1; + else + return 1 - std::exp(-qPow(qreal(10.0), volume / qreal(20.0)) * LOG100); + case DecibelVolumeScale: + return volume; + } + break; + } + + return volume; +} + +} + #ifndef QT_NO_DEBUG_STREAM QDebug operator<<(QDebug dbg, QAudio::Error error) { @@ -210,6 +342,28 @@ QDebug operator<<(QDebug dbg, QAudio::Role role) } return dbg; } + +QDebug operator<<(QDebug dbg, QAudio::VolumeScale scale) +{ + QDebugStateSaver saver(dbg); + dbg.nospace(); + switch (scale) { + case QAudio::LinearVolumeScale: + dbg << "LinearVolumeScale"; + break; + case QAudio::CubicVolumeScale: + dbg << "CubicVolumeScale"; + break; + case QAudio::LogarithmicVolumeScale: + dbg << "LogarithmicVolumeScale"; + break; + case QAudio::DecibelVolumeScale: + dbg << "DecibelVolumeScale"; + break; + } + return dbg; +} + #endif |