obs: Use new fader from libobs for volume control

This replaces the code for volume control with a newer version that
uses the new fader implementation in order to control the fader/slider
position and source volume.
The volume label will now indicate the gain in dB instead of percent,
mainly because it looks cool and is easy to do.
Due to libobs saving the multiplier option for the source instead of
the slider/fader positon, existing volume levels will (mostly) stay
the same with only the slider beeing at a different position.
This is of course within the resolution of the slider (100 steps).

obs/volume-control.cpp

@@ -39,10 +39,10 @@ static inline float DBToLinear(float db_full)
 
 void VolControl::OBSVolumeChanged(void *data, calldata_t *calldata)
 {
+	Q_UNUSED(calldata);
 	VolControl *volControl = static_cast<VolControl*>(data);
-	int vol = (int)(calldata_float(calldata, "volume") * 100.0f + 0.5f);
 
-	QMetaObject::invokeMethod(volControl, "VolumeChanged", Q_ARG(int, vol));
+	QMetaObject::invokeMethod(volControl, "VolumeChanged");
 }
 
 void VolControl::OBSVolumeLevel(void *data, calldata_t *calldata)
@@ -58,11 +58,9 @@ void VolControl::OBSVolumeLevel(void *data, calldata_t *calldata)
 		Q_ARG(float, peakHold));
 }
 
-void VolControl::VolumeChanged(int vol)
+void VolControl::VolumeChanged()
 {
-	signalChanged = false;
-	slider->setValue(vol);
-	signalChanged = true;
+	slider->setValue((int) (obs_fader_get_deflection(obs_fader) * 100.0f));
 }
 
 void VolControl::VolumeLevel(float mag, float peak, float peakHold)
@@ -85,17 +83,9 @@ void VolControl::VolumeLevel(float mag, float peak, float peakHold)
 
 void VolControl::SliderChanged(int vol)
 {
-	if (signalChanged) {
-		signal_handler_disconnect(obs_source_get_signal_handler(source),
-				"volume", OBSVolumeChanged, this);
-
-		obs_source_set_volume(source, float(vol)*0.01f);
-
-		signal_handler_connect(obs_source_get_signal_handler(source),
-				"volume", OBSVolumeChanged, this);
-	}
-
-	volLabel->setText(QString::number(vol));
+	obs_fader_set_deflection(obs_fader, float(vol) * 0.01f);
+	volLabel->setText(QString::number(obs_fader_get_db(obs_fader), 'f', 1)
+			.append(" dB"));
 }
 
 QString VolControl::GetName() const
@@ -110,14 +100,13 @@ void VolControl::SetName(const QString &newName)
 
 VolControl::VolControl(OBSSource source_)
 	: source        (source_),
-	  signalChanged (true),
 	  lastMeterTime (0),
 	  levelTotal    (0.0f),
-	  levelCount    (0.0f)
+	  levelCount    (0.0f),
+	  obs_fader     (obs_fader_create(OBS_FADER_CUBIC))
 {
 	QVBoxLayout *mainLayout = new QVBoxLayout();
 	QHBoxLayout *textLayout = new QHBoxLayout();
-	int         vol         = int(obs_source_get_volume(source) * 100.0f);
 
 	nameLabel = new QLabel();
 	volLabel  = new QLabel();
@@ -129,11 +118,10 @@ VolControl::VolControl(OBSSource source_)
 
 	nameLabel->setText(obs_source_get_name(source));
 	nameLabel->setFont(font);
-	volLabel->setText(QString::number(vol));
 	volLabel->setFont(font);
 	slider->setMinimum(0);
 	slider->setMaximum(100);
-	slider->setValue(vol);
+
 //	slider->setMaximumHeight(13);
 
 	textLayout->setContentsMargins(0, 0, 0, 0);
@@ -150,23 +138,29 @@ VolControl::VolControl(OBSSource source_)
 
 	setLayout(mainLayout);
 
-	signal_handler_connect(obs_source_get_signal_handler(source),
-			"volume", OBSVolumeChanged, this);
+	signal_handler_connect(obs_fader_get_signal_handler(obs_fader),
+			"volume_changed", OBSVolumeChanged, this);
 
 	signal_handler_connect(obs_source_get_signal_handler(source),
 		"volume_level", OBSVolumeLevel, this);
 
 	QWidget::connect(slider, SIGNAL(valueChanged(int)),
 			this, SLOT(SliderChanged(int)));
+
+	obs_fader_attach_source(obs_fader, source);
+	/* Call volume changed once to init the slider position and label */
+	VolumeChanged();
 }
 
 VolControl::~VolControl()
 {
-	signal_handler_disconnect(obs_source_get_signal_handler(source),
-			"volume", OBSVolumeChanged, this);
+	signal_handler_disconnect(obs_fader_get_signal_handler(obs_fader),
+			"volume_changed", OBSVolumeChanged, this);
 
 	signal_handler_disconnect(obs_source_get_signal_handler(source),
 		"volume_level", OBSVolumeLevel, this);
+
+	obs_fader_destroy(obs_fader);
 }
 
 VolumeMeter::VolumeMeter(QWidget *parent)

obs/volume-control.hpp

@@ -32,16 +32,16 @@ private:
 	QLabel          *volLabel;
 	VolumeMeter     *volMeter;
 	QSlider         *slider;
-	bool            signalChanged;
 	uint64_t        lastMeterTime;
 	float           levelTotal;
 	float           levelCount;
+	obs_fader_t     *obs_fader;
 
 	static void OBSVolumeChanged(void *param, calldata_t *calldata);
 	static void OBSVolumeLevel(void *data, calldata_t *calldata);
 
 private slots:
-	void VolumeChanged(int vol);
+	void VolumeChanged();
 	void VolumeLevel(float mag, float peak, float peakHold);
 	void SliderChanged(int vol);