Add "natural" scrolling support for trackpads (#5510)

Adds QWheelEvent::inverted() support to spinboxes, knobs, sliders

src/gui/clips/MidiClipView.cpp

@@ -334,16 +334,16 @@ void MidiClipView::wheelEvent(QWheelEvent * we)
 		}
 
 		Note * n = m_clip->noteAtStep( step );
-		if(!n && we->angleDelta().y() > 0)
+		const int direction = (we->angleDelta().y() > 0 ? 1 : -1) * (we->inverted() ? -1 : 1);
+		if(!n && direction > 0)
 		{
 			n = m_clip->addStepNote( step );
 			n->setVolume( 0 );
 		}
 		if( n != nullptr )
 		{
 			int vol = n->getVolume();
-
-			if(we->angleDelta().y() > 0)
+			if(direction > 0)
 			{
 				n->setVolume( qMin( 100, vol + 5 ) );
 			}

src/gui/editors/PianoRoll.cpp

@@ -3785,7 +3785,8 @@ void PianoRoll::wheelEvent(QWheelEvent * we )
 		}
 		if( nv.size() > 0 )
 		{
-			const int step = we->angleDelta().y() > 0 ? 1 : -1;
+			const int step = (we->angleDelta().y() > 0 ? 1 : -1) * (we->inverted() ? -1 : 1);
+
 			if( m_noteEditMode == NoteEditMode::Volume )
 			{
 				for ( Note * n : nv )

src/gui/widgets/ComboBox.cpp

@@ -223,7 +223,8 @@ void ComboBox::wheelEvent( QWheelEvent* event )
 {
 	if( model() )
 	{
-		model()->setInitValue(model()->value() + ((event->angleDelta().y() < 0) ? 1 : -1));
+		const int direction = (event->angleDelta().y() < 0 ? 1 : -1) * (event->inverted() ? -1 : 1);
+		model()->setInitValue(model()->value() + direction);
 		update();
 		event->accept();
 	}

src/gui/widgets/Fader.cpp

@@ -196,15 +196,9 @@ void Fader::mouseReleaseEvent(QMouseEvent* mouseEvent)
 void Fader::wheelEvent (QWheelEvent* ev)
 {
 	ev->accept();
+	const int direction = (ev->angleDelta().y() > 0 ? 1 : -1) * (ev->inverted() ? -1 : 1);
 
-	if (ev->angleDelta().y() > 0)
-	{
-		model()->incValue(1);
-	}
-	else
-	{
-		model()->incValue(-1);
-	}
+	model()->incValue(direction);
 	updateTextFloat();
 	s_textFloat->setVisibilityTimeOut(1000);
 }

src/gui/widgets/FloatModelEditorBase.cpp

@@ -330,6 +330,11 @@ void FloatModelEditorBase::wheelEvent(QWheelEvent * we)
 		}
 	}
 
+	// Handle "natural" scrolling, which is common on trackpads and touch devices
+	if (we->inverted()) {
+		direction = -direction;
+	}
+
 	// Compute the number of steps but make sure that we always do at least one step
 	const float stepMult = std::max(range / numberOfStepsForFullSweep / step, 1.f);
 	const int inc = direction * stepMult;

src/gui/widgets/LcdSpinBox.cpp

@@ -144,7 +144,9 @@ void LcdSpinBox::mouseReleaseEvent(QMouseEvent*)
 void LcdSpinBox::wheelEvent(QWheelEvent * we)
 {
 	we->accept();
-	model()->setValue(model()->value() + ((we->angleDelta().y() > 0) ? 1 : -1) * model()->step<int>());
+	const int direction = (we->angleDelta().y() > 0 ? 1 : -1) * (we->inverted() ? -1 : 1);
+
+	model()->setValue(model()->value() + direction * model()->step<int>());
 	emit manualChange();
 }