From 37d795cf7b8806cedfdba2518c257f3ae997eaab Mon Sep 17 00:00:00 2001
From: nazar-kutz <vitaminkuna@gmail.com>
Date: Sat, 6 Mar 2021 01:55:08 +0200
Subject: [PATCH] improve the readability of the algorithm for checking that
 one region is inside another

---
 .../main/java/net/osmand/map/WorldRegion.java | 43 ++++++++-----------
 .../main/java/net/osmand/util/Algorithms.java | 41 ++++++++++++++++++
 2 files changed, 58 insertions(+), 26 deletions(-)

diff --git a/OsmAnd-java/src/main/java/net/osmand/map/WorldRegion.java b/OsmAnd-java/src/main/java/net/osmand/map/WorldRegion.java
index 45bd14f600..b1be29d5fa 100644
--- a/OsmAnd-java/src/main/java/net/osmand/map/WorldRegion.java
+++ b/OsmAnd-java/src/main/java/net/osmand/map/WorldRegion.java
@@ -3,6 +3,7 @@ package net.osmand.map;
 import net.osmand.data.LatLon;
 import net.osmand.data.QuadRect;
 import net.osmand.util.Algorithms;
+import net.osmand.util.Algorithms.Point2D;
 
 import java.io.Serializable;
 import java.util.LinkedList;
@@ -187,37 +188,27 @@ public class WorldRegion implements Serializable {
 	}
 
 	public boolean containsRegion(WorldRegion region) {
-		boolean isBoundingAvailable = this.boundingBox != null && region.boundingBox != null;
-		boolean isPolygonsAvailable = this.polygon != null && region.polygon != null;
-
-		boolean containsBox = false;
-		if (isBoundingAvailable) {
-			containsBox = this.boundingBox.contains(region.boundingBox);
-		}
-		if (containsBox && isPolygonsAvailable) {
-			boolean allPointsInsideThePolygon = true;
-			List<LatLon> regionPolygon = region.polygon;
-			for (int i = 0; i < regionPolygon.size(); i++) {
-				allPointsInsideThePolygon = isPointInsideThePolygon(regionPolygon.get(i));
-				if (!allPointsInsideThePolygon) {
-					return false;
-				}
-			}
-			return true;
+		if (containsBoundingBox(region.boundingBox)) {
+			// check polygon only if bounding box match
+			return containsPolygon(region.polygon);
 		}
 		return false;
 	}
 
-	private boolean isPointInsideThePolygon(LatLon test) {
-		boolean result = false;
-		for (int i = 0, j = polygon.size() - 1; i < polygon.size(); j = i++) {
-			if ((polygon.get(i).getLongitude() > test.getLongitude()) != (polygon.get(j).getLongitude() > test.getLongitude()) &&
-					(test.getLatitude() < (polygon.get(j).getLatitude() - polygon.get(i).getLatitude()) * (test.getLongitude() - polygon.get(i).getLongitude())
-							/ (polygon.get(j).getLongitude()-polygon.get(i).getLongitude()) + polygon.get(i).getLatitude())) {
-				result = !result;
-			}
+	private boolean containsBoundingBox(QuadRect rectangle) {
+		if (boundingBox != null && rectangle != null) {
+			return boundingBox.contains(rectangle);
 		}
-		return result;
+		return false;
+	}
+
+	private boolean containsPolygon(List<LatLon> another) {
+		if (polygon != null && another != null) {
+			Point2D[] inner = Algorithms.createPoint2DArrayFromLatLon(polygon);
+			Point2D[] outer = Algorithms.createPoint2DArrayFromLatLon(another);
+			return Algorithms.isFirstPolygonInsideTheSecond(outer, inner);
+		}
+		return false;
 	}
 
 	public boolean isContinent() {
diff --git a/OsmAnd-java/src/main/java/net/osmand/util/Algorithms.java b/OsmAnd-java/src/main/java/net/osmand/util/Algorithms.java
index 36c0034a26..b539ca8363 100644
--- a/OsmAnd-java/src/main/java/net/osmand/util/Algorithms.java
+++ b/OsmAnd-java/src/main/java/net/osmand/util/Algorithms.java
@@ -2,6 +2,7 @@ package net.osmand.util;
 
 import net.osmand.IProgress;
 import net.osmand.PlatformUtil;
+import net.osmand.data.LatLon;
 
 import org.apache.commons.logging.Log;
 import org.xmlpull.v1.XmlPullParser;
@@ -117,6 +118,46 @@ public class Algorithms {
 		}
 		return def;
 	}
+
+	public static class Point2D {
+		public double x;
+		public double y;
+	}
+
+	public static Point2D[] createPoint2DArrayFromLatLon(List<LatLon> latLons) {
+		Point2D[] array = new Point2D[latLons.size()];
+		for (int i = 0; i < array.length; i++) {
+			Point2D point = new Point2D();
+			point.x = latLons.get(i).getLatitude();
+			point.y = latLons.get(i).getLongitude();
+			array[i] = point;
+		}
+		return array;
+	}
+
+	public static boolean isFirstPolygonInsideTheSecond(Point2D[] first,
+	                                                    Point2D[] second) {
+		for (Point2D point : first) {
+			if (!isPointInsideTheBoundary(point, second)) {
+				// if at least one point is not inside the boundary, return false
+				return false;
+			}
+		}
+		return true;
+	}
+
+	public static boolean isPointInsideTheBoundary(Point2D point,
+	                                               Point2D[] polygon) {
+		boolean result = false;
+		for (int i = 0, j = polygon.length - 1; i < polygon.length; j = i++) {
+			if ((polygon[i].y > point.y) != (polygon[j].y > point.y)
+					&& (point.x < (polygon[j].x - polygon[i].x) * (point.y - polygon[i].y) /
+					(polygon[j].y-polygon[i].y) + polygon[i].x)) {
+				result = !result;
+			}
+		}
+		return result;
+	}
 	
 	public static int parseIntSilently(String input, int def) {
 		if (input != null && input.length() > 0) {