Enable horizontal direction of manipulation

Extend `FloatModelEditorBase` so that it also allows manipulation of the
values when the mouse is moved in horizontal directions. The default is
to use the vertical direction.

Make use of this new feature in `BarModelEditor` which now reacts to
horizontal movements when changing values.

src/gui/widgets/BarModelEditor.cpp

@@ -7,7 +7,7 @@ namespace lmms::gui
 {
 
 BarModelEditor::BarModelEditor(QString text, FloatModel * floatModel, QWidget * parent) :
-	FloatModelEditorBase(parent),
+	FloatModelEditorBase(DirectionOfManipulation::Horizontal, parent),
 	m_text(text)
 {
 	setModel(floatModel);

src/gui/widgets/FloatModelEditorBase.cpp

@@ -51,12 +51,13 @@ namespace lmms::gui
 
 SimpleTextFloat * FloatModelEditorBase::s_textFloat = nullptr;
 
-FloatModelEditorBase::FloatModelEditorBase(QWidget * _parent, const QString & _name ) :
+FloatModelEditorBase::FloatModelEditorBase(DirectionOfManipulation directionOfManipulation, QWidget * _parent, const QString & _name ) :
 	QWidget( _parent ),
 	FloatModelView( new FloatModel( 0, 0, 0, 1, nullptr, _name, true ), this ),
 	m_volumeKnob( false ),
 	m_volumeRatio( 100.0, 0.0, 1000000.0 ),
-	m_buttonPressed( false )
+	m_buttonPressed( false ),
+	m_directionOfManipulation(directionOfManipulation)
 {
 	initUi( _name );
 }
@@ -80,10 +81,11 @@ void FloatModelEditorBase::initUi( const QString & _name )
 
 float FloatModelEditorBase::getValue( const QPoint & _p )
 {
-	float value;
+	// Find out which direction/coordinate is relevant for this control
+	int const coordinate = m_directionOfManipulation == DirectionOfManipulation::Vertical ? _p.y() : -_p.x();
 
 	// knob value increase is linear to mouse movement
-	value = .4f * _p.y();
+	float value = .4f * coordinate;
 
 	// if shift pressed we want slower movement
 	if( getGUI()->mainWindow()->isShiftPressed() )