Improve drag & drop behaviour of macro segments

- Depending on the drop position you can either drop before or after a
  widget
- Added a visual indicator where the macro segment will be dropped

src/headers/macro-segment-list.hpp

@@ -31,15 +31,22 @@ protected:
 	void mousePressEvent(QMouseEvent *event);
 	void mouseMoveEvent(QMouseEvent *event);
 	void mouseReleaseEvent(QMouseEvent *event);
+	void dragLeaveEvent(QDragLeaveEvent *event);
 	void dragEnterEvent(QDragEnterEvent *event);
+	void dragMoveEvent(QDragMoveEvent *event);
 	void dropEvent(QDropEvent *event);
 
 private:
-	int GetIndex(QPoint);
-	int GetDropIndex(QPoint);
+	int GetDragIndex(const QPoint &);
+	int GetDropIndex(const QPoint &);
+	int GetWidgetIdx(const QPoint &);
+	bool IsInListArea(const QPoint &);
 	QRect GetContentItemRectWithPadding(int idx);
+	void HideLastDropLine();
+	MacroSegmentEdit *WidgetAt(int idx);
 
 	int _dragPosition = -1;
+	int _dropLineIdx = -1;
 
 	QVBoxLayout *_layout;
 	QVBoxLayout *_contentLayout;

src/headers/macro-segment.hpp

@@ -63,15 +63,38 @@ protected:
 	Section *_section;
 	QLabel *_headerInfo;
 	QWidget *_frame;
-	QFrame *_noBorderframe;
-	QFrame *_borderFrame;
 	QVBoxLayout *_contentLayout;
 
 private:
+	enum class DropLineState {
+		NONE,
+		ABOVE,
+		BELOW,
+	};
+
 	virtual MacroSegment *Data() = 0;
+	void ShowDropLine(DropLineState);
+
+	// The reason for using two separate frame widget each with their own
+	// stylesheet and changing their visibility vs. using a single frame
+	// and changing the stylesheet at runtime is that the operation of
+	// adjusting the stylesheet is very expensive and can take multiple
+	// hundred milliseconds per widget.
+	// This performance impact would hurt in areas like drag and drop or
+	// emitting the "SelectionChanged" signal.
+	QFrame *_noBorderframe;
+	QFrame *_borderFrame;
+
+	// In most cases the line above the widget will be used.
+	// The lower one will only be used if the segment is the last one in
+	// the list.
+	QFrame *_dropLineAbove;
+	QFrame *_dropLineBelow;
 
 	bool _showHighlight;
 	QTimer _timer;
+
+	friend class MacroSegmentList;
 };
 
 class MouseWheelWidgetAdjustmentGuard : public QObject {