Added support for line "dy" parameter

src/map/mapsforge/rastertile.cpp

@@ -1,3 +1,4 @@
+#include <cmath>
 #include <QPainter>
 #include <QCache>
 #include "common/programpaths.h"
@@ -8,6 +9,8 @@ using namespace Mapsforge;
 
 #define TEXT_EXTENT 160
 
+static double limit = cos(deg2rad(170));
+
 static qreal area(const QPainterPath &polygon)
 {
 	qreal area = 0;
@@ -55,6 +58,47 @@ static const QColor *haloColor(const Style::TextRender *ti)
 	  ? &ti->strokeColor() : 0;
 }
 
+static QPainterPath parallelPath(const QPainterPath &p, double dy)
+{
+	int n = p.elementCount() - 1;
+	QVector<QPointF> u(n);
+	QPainterPath h;
+
+#if QT_VERSION >= QT_VERSION_CHECK(5, 13, 0)
+	h.reserve(p.elementCount());
+#endif // QT 5.13
+
+	for (int k = 0; k < n; k++) {
+		qreal c = p.elementAt(k + 1).x - p.elementAt(k).x;
+		qreal s = p.elementAt(k + 1).y - p.elementAt(k).y;
+		qreal l = sqrt(c * c + s * s);
+
+		u[k] = (l == 0) ? QPointF(0, 0) : QPointF(c / l, s / l);
+
+		if (k == 0)
+			continue;
+		if (u.at(k).x() * u.at(k-1).x() + u.at(k).y() * u.at(k-1).y() < limit)
+			return p;
+	}
+
+	h.moveTo(QPointF(p.elementAt(0).x - dy * u.at(0).y(),
+	  p.elementAt(0).y + dy * u.at(0).x()));
+
+	for (int k = 1; k < n; k++) {
+		qreal l = dy / (1 + u.at(k).x() * u.at(k-1).x()
+		  + u.at(k).y() * u.at(k-1).y());
+		QPainterPath::Element e(p.elementAt(k));
+
+		h.lineTo(QPointF(e.x - l * (u.at(k).y() + u.at(k-1).y()),
+		  e.y + l * (u.at(k).x() + u.at(k-1).x())));
+	}
+
+	h.lineTo(QPointF(p.elementAt(n).x - dy * u.at(n-1).y(),
+	  p.elementAt(n).y + dy * u.at(n-1).x()));
+
+	return h;
+}
+
 void RasterTile::processPointLabels(const QList<MapData::Point> &points,
   QList<TextItem*> &textItems)
 {
@@ -306,13 +350,17 @@ void RasterTile::drawPaths(QPainter *painter, const QList<MapData::Path> &paths,
 
 		if (path) {
 			const Style::PathRender *ri = is.pathRender();
+			qreal dy = ri->dy(_zoom);
 
 			if (!path->pp.elementCount())
 				path->pp = painterPath(path->path->poly, ri->curve());
 
 			painter->setPen(ri->pen(_zoom));
 			painter->setBrush(ri->brush());
-			painter->drawPath(path->pp);
+			if (dy != 0)
+				painter->drawPath(parallelPath(path->pp, dy));
+			else
+				painter->drawPath(path->pp);
 		} else {
 			const Style::CircleRender *ri = is.circleRender();
 			qreal radius = ri->radius(_zoom);

src/map/mapsforge/style.cpp

@@ -245,6 +245,13 @@ void Style::line(QXmlStreamReader &reader, const Rule &rule)
 		if (curve == "cubic")
 			ri._curve = true;
 	}
+	if (attr.hasAttribute("dy")) {
+		ri._dy = attr.value("dy").toDouble(&ok);
+		if (!ok) {
+			reader.raiseError("invalid dy value");
+			return;
+		}
+	}
 
 	if (ri.rule()._type == Rule::AnyType || ri.rule()._type == Rule::WayType)
 		_paths.append(ri);
@@ -689,6 +696,11 @@ QPen Style::PathRender::pen(int zoom) const
 		return Qt::NoPen;
 }
 
+qreal Style::PathRender::dy(int zoom) const
+{
+	return (_scale && zoom >= 12) ? pow(1.5, zoom - 12) * _dy : _dy;
+}
+
 qreal Style::CircleRender::radius(int zoom) const
 {
 	return (_scale && zoom >= 12) ? pow(1.5, zoom - 12) * _radius : _radius;

src/map/mapsforge/style.h

@@ -137,13 +137,14 @@ public:
 		PathRender(const Rule &rule, int zOrder) : Render(rule),
 		  _zOrder(zOrder), _strokeWidth(0), _strokeCap(Qt::RoundCap),
 			_strokeJoin(Qt::RoundJoin), _area(false), _curve(false),
-			_scale(Stroke) {}
+			_scale(Stroke), _dy(0) {}
 
 		int zOrder() const {return _zOrder;}
 		QPen pen(int zoom) const;
 		const QBrush &brush() const {return _brush;}
 		bool area() const {return _area;}
 		bool curve() const {return _curve;}
+		qreal dy(int zoom) const;
 
 	private:
 		friend class Style;
@@ -159,6 +160,7 @@ public:
 		QBrush _brush;
 		bool _area, _curve;
 		Scale _scale;
+		qreal _dy;
 	};
 
 	class CircleRender : public Render