Zooming with mouse wheel center (#3835)

* Horizontal mouse-wheel zooming. Ensure zoom center is always on the current mouse position.

* Horizontal zoom using mouse wheel center on the mouse position. For the SongEditor too.

* Wheel center on the Automation editor too.

include/SongEditor.h

@@ -135,6 +135,7 @@ private slots:
 
 	bool m_scrollBack;
 	bool m_smoothScroll;
+	int m_widgetWidthTotal;
 
 	EditMode m_mode;
 	EditMode m_ctrlMode; // mode they were in before they hit ctrl

src/gui/editors/AutomationEditor.cpp

@@ -1680,6 +1680,17 @@ void AutomationEditor::wheelEvent(QWheelEvent * we )
 			x--;
 		}
 		x = qBound( 0, x, m_zoomingXModel.size() - 1 );
+
+		int mouseX = (we->x() - VALUES_WIDTH)* MidiTime::ticksPerTact();
+		// ticks based on the mouse x-position where the scroll wheel was used
+		int ticks = mouseX / m_ppt;
+		// what would be the ticks in the new zoom level on the very same mouse x
+		int newTicks = mouseX / (DEFAULT_PPT * m_zoomXLevels[x]);
+
+		// scroll so the tick "selected" by the mouse x doesn't move on the screen
+		m_leftRightScroll->setValue(m_leftRightScroll->value() + ticks - newTicks);
+
+
 		m_zoomingXModel.setValue( x );
 	}
 	else if( we->modifiers() & Qt::ShiftModifier

src/gui/editors/PianoRoll.cpp

@@ -3296,6 +3296,14 @@ void PianoRoll::wheelEvent(QWheelEvent * we )
 			z--;
 		}
 		z = qBound( 0, z, m_zoomingModel.size() - 1 );
+
+		int x = (we->x() - WHITE_KEY_WIDTH)* MidiTime::ticksPerTact();
+		// ticks based on the mouse x-position where the scroll wheel was used
+		int ticks = x / m_ppt;
+		// what would be the ticks in the new zoom level on the very same mouse x
+		int newTicks = x / (DEFAULT_PR_PPT * m_zoomLevels[z]);
+		// scroll so the tick "selected" by the mouse x doesn't move on the screen
+		m_leftRightScroll->setValue(m_leftRightScroll->value() + ticks - newTicks);
 		// update combobox with zooming-factor
 		m_zoomingModel.setValue( z );
 	}

src/gui/editors/SongEditor.cpp

@@ -82,11 +82,11 @@ SongEditor::SongEditor( Song * song ) :
 {
 	m_zoomingModel->setParent(this);
 	// create time-line
-	int widgetTotal = ConfigManager::inst()->value( "ui",
+	m_widgetWidthTotal = ConfigManager::inst()->value( "ui",
 							"compacttrackbuttons" ).toInt()==1 ?
 		DEFAULT_SETTINGS_WIDGET_WIDTH_COMPACT + TRACK_OP_WIDTH_COMPACT :
 		DEFAULT_SETTINGS_WIDGET_WIDTH + TRACK_OP_WIDTH;
-	m_timeLine = new TimeLineWidget( widgetTotal, 32,
+	m_timeLine = new TimeLineWidget( m_widgetWidthTotal, 32,
 					pixelsPerTact(),
 					m_song->m_playPos[Song::Mode_PlaySong],
 					m_currentPosition,
@@ -385,6 +385,16 @@ void SongEditor::wheelEvent( QWheelEvent * we )
 			z--;
 		}
 		z = qBound( 0, z, m_zoomingModel->size() - 1 );
+
+
+		int x = (we->x() - m_widgetWidthTotal);
+		// tact based on the mouse x-position where the scroll wheel was used
+		int tact= x  / pixelsPerTact();
+		// what would be the tact in the new zoom level on the very same mouse x
+		int newTact = x / DEFAULT_PIXELS_PER_TACT / m_zoomLevels[z];
+		// scroll so the tact "selected" by the mouse x doesn't move on the screen
+		m_leftRightScroll->setValue(m_leftRightScroll->value() + tact - newTact);
+
 		// update combobox with zooming-factor
 		m_zoomingModel->setValue( z );