Provide a setting for system default input

Provide the setting "[System Default]" which instructs the SDL driver to
use the default device of the system as the input device. In the
configuration file this option is represented as an empty string. This
should play well with the current existing configuration of the users.

include/AudioSdl.h

@@ -69,6 +69,8 @@ class AudioSdl : public AudioDevice
 	private:
 		QLineEdit * m_device;
 		QComboBox* m_inputDeviceComboBox = nullptr;
+
+		static QString s_defaultInputDevice;
 	} ;
 
 

src/core/audio/AudioSdl.cpp

@@ -109,13 +109,14 @@ AudioSdl::AudioSdl( bool & _success_ful, AudioEngine*  _audioEngine ) :
 	m_inputAudioHandle.callback = sdlInputAudioCallback;
 
 	const QString inputDevice = ConfigManager::inst()->value("audiosdl", "inputdevice");
+	const bool isDefaultInput = inputDevice.isEmpty();
 
 	// Try with the configured device
-	const auto inputDeviceCStr = inputDevice.toLocal8Bit().data();
+	const auto inputDeviceCStr = isDefaultInput ? nullptr : inputDevice.toLocal8Bit().data();
 	m_inputDevice = SDL_OpenAudioDevice (inputDeviceCStr, 1, &m_inputAudioHandle, &actual, 0);
 
-	// If we did not get a device ID try again with the default device
-	if (m_inputDevice == 0)
+	// If we did not get a device ID try again with the default device if we did not try that before
+	if (m_inputDevice == 0 && !isDefaultInput)
 	{
 		m_inputDevice = SDL_OpenAudioDevice(nullptr, 1, &m_inputAudioHandle, &actual, 0);
 	}
@@ -290,6 +291,8 @@ void AudioSdl::sdlInputAudioCallback(Uint8 *_buf, int _len) {
 
 #endif
 
+QString AudioSdl::setupWidget::s_defaultInputDevice = QObject::tr("[System Default]");
+
 AudioSdl::setupWidget::setupWidget( QWidget * _parent ) :
 	AudioDeviceSetupWidget( AudioSdl::name(), _parent )
 {
@@ -303,6 +306,8 @@ AudioSdl::setupWidget::setupWidget( QWidget * _parent ) :
 	m_inputDeviceComboBox = new QComboBox(this);
 
 #ifdef LMMS_HAVE_SDL2
+	m_inputDeviceComboBox->addItem(s_defaultInputDevice);
+
 	const int numberOfInputDevices = SDL_GetNumAudioDevices(1);
 	for (int i = 0; i < numberOfInputDevices; ++i)
 	{
@@ -312,7 +317,14 @@ AudioSdl::setupWidget::setupWidget( QWidget * _parent ) :
 
 	// Set the current device to the one in the configuration
 	const auto inputDevice = ConfigManager::inst()->value("audiosdl", "inputdevice");
-	m_inputDeviceComboBox->setCurrentText(inputDevice);
+	if (inputDevice.isEmpty())
+	{
+		m_inputDeviceComboBox->setCurrentText(s_defaultInputDevice);
+	}
+	else
+	{
+		m_inputDeviceComboBox->setCurrentText(inputDevice);
+	}
 #endif
 
 	form->addRow(tr("Input device"), m_inputDeviceComboBox);
@@ -327,7 +339,12 @@ void AudioSdl::setupWidget::saveSettings()
 							m_device->text() );
 
 	const auto currentInputDevice = m_inputDeviceComboBox->currentText();
-	if (!currentInputDevice.isEmpty())
+	if (currentInputDevice == s_defaultInputDevice)
+	{
+		// Represent the default input device with an empty string
+		ConfigManager::inst()->setValue("audiosdl", "inputdevice", "");
+	}
+	else if (!currentInputDevice.isEmpty())
 	{
 		ConfigManager::inst()->setValue("audiosdl", "inputdevice", currentInputDevice);
 	}