Create centroids based on non clipped ways (#734)

- introduced a new member to the MapElement to store the pre-calculated centroid of the way (none clipped)
- auto create element.centroidPosition based on all (none clipped) points of a osm-way
- skipping rendering of centered symbols, if OFF screen
- introduced Parameter to enable/disable the feature

vtm/src/org/oscim/core/MapElement.java

@@ -3,6 +3,7 @@
  * Copyright 2016 Andrey Novikov
  * Copyright 2017-2019 Gustl22
  * Copyright 2018-2019 devemux86
+ * Copyright 2019 marq24
  *
  * This file is part of the OpenScienceMap project (http://www.opensciencemap.org).
  *
@@ -30,7 +31,7 @@ import org.oscim.theme.IRenderTheme;
  */
 public class MapElement extends GeometryBuffer {
 
-    public PointF labelPosition;
+    public PointF centroidPosition, labelPosition;
 
     /**
      * layer of the element (0-10) overrides the theme drawing order.
@@ -57,6 +58,7 @@ public class MapElement extends GeometryBuffer {
     public MapElement(MapElement element) {
         super(element);
         this.tags.set(element.tags.asArray());
+        this.centroidPosition = element.centroidPosition;
         this.labelPosition = element.labelPosition;
         this.setLayer(element.layer);
     }
@@ -101,6 +103,10 @@ public class MapElement extends GeometryBuffer {
                 || "building:part".equals(tags.getValue("layer")); // OpenMapTiles
     }
 
+    public void setCentroidPosition(float x, float y) {
+        centroidPosition = new PointF(x, y);
+    }
+
     public void setLabelPosition(float x, float y) {
         labelPosition = new PointF(x, y);
     }
@@ -122,6 +128,10 @@ public class MapElement extends GeometryBuffer {
     @Override
     public MapElement scale(float scaleX, float scaleY) {
         super.scale(scaleX, scaleY);
+        if (centroidPosition != null) {
+            centroidPosition.x *= scaleX;
+            centroidPosition.y *= scaleY;
+        }
         if (labelPosition != null) {
             labelPosition.x *= scaleX;
             labelPosition.y *= scaleY;
@@ -132,6 +142,10 @@ public class MapElement extends GeometryBuffer {
     @Override
     public MapElement translate(float dx, float dy) {
         super.translate(dx, dy);
+        if (centroidPosition != null) {
+            centroidPosition.x += dx;
+            centroidPosition.y += dy;
+        }
         if (labelPosition != null) {
             labelPosition.x += dx;
             labelPosition.y += dy;

vtm/src/org/oscim/layers/tile/vector/labeling/LabelTileLoaderHook.java

@@ -2,6 +2,7 @@
  * Copyright 2013 Hannes Janetzek
  * Copyright 2016-2018 devemux86
  * Copyright 2016 Andrey Novikov
+ * Copyright 2019 marq24
  *
  * This file is part of the OpenScienceMap project (http://www.opensciencemap.org).
  *
@@ -32,9 +33,7 @@ import org.oscim.theme.styles.TextStyle;
 import org.oscim.utils.Parameters;
 import org.oscim.utils.geom.PolyLabel;
 
-import static org.oscim.core.GeometryBuffer.GeometryType.LINE;
+import static org.oscim.core.GeometryBuffer.GeometryType.*;
-import static org.oscim.core.GeometryBuffer.GeometryType.POINT;
-import static org.oscim.core.GeometryBuffer.GeometryType.POLY;
 import static org.oscim.layers.tile.vector.labeling.LabelLayer.LABEL_DATA;
 
 public class LabelTileLoaderHook implements TileLoaderThemeHook {
@@ -135,6 +134,8 @@ public class LabelTileLoaderHook implements TileLoaderThemeHook {
                 }
             } else if (element.type == POLY) {
                 PointF centroid = element.labelPosition;
+                if (centroid == null)
+                    centroid = element.centroidPosition;
                 if (!Parameters.POLY_SYMBOL) {
                     if (centroid == null)
                         return false;

vtm/src/org/oscim/tiling/source/mapfile/MapDatabase.java

@@ -6,6 +6,7 @@
  * Copyright 2016 Andrey Novikov
  * Copyright 2017-2018 Gustl22
  * Copyright 2018 Bezzu
+ * Copyright 2019 marq24
  *
  * This file is part of the OpenScienceMap project (http://www.opensciencemap.org).
  *
@@ -968,6 +969,26 @@ public class MapDatabase implements ITileDataSource {
 
                 mTileProjection.project(e);
 
+                // When a way will be rendered then typically a label / symbol will be applied
+                // by the render theme. If the way does not come with a defined labelPosition
+                // we should calculate a position, that is based on all points of the given way.
+                // This "auto" position calculation is also done in the LabelTileLoaderHook class
+                // but then the points of the way have been already reduced cause of the clipping
+                // that is happening. So the suggestion here is to calculate the centroid of the way
+                // and use that as centroidPosition of the element.
+                if (Parameters.POLY_CENTROID && e.labelPosition == null) {
+                    float x = 0;
+                    float y = 0;
+                    int n = e.index[0];
+                    for (int i = 0; i < n; ) {
+                        x += e.points[i++];
+                        y += e.points[i++];
+                    }
+                    x /= (n / 2);
+                    y /= (n / 2);
+                    e.setCentroidPosition(x, y);
+                }
+
                 // Avoid clipping for buildings, which slows rendering.
                 // But clip everything if buildings are displayed.
                 if (!e.tags.containsKey(Tag.KEY_BUILDING)
@@ -1277,6 +1298,10 @@ public class MapDatabase implements ITileDataSource {
                 e.labelPosition.x = projectLon(e.labelPosition.x);
                 e.labelPosition.y = projectLat(e.labelPosition.y);
             }
+            if (e.centroidPosition != null) {
+                e.centroidPosition.x = projectLon(e.centroidPosition.x);
+                e.centroidPosition.y = projectLat(e.centroidPosition.y);
+            }
         }
     }
 }

vtm/src/org/oscim/utils/Parameters.java

@@ -41,6 +41,12 @@ public final class Parameters {
      */
     public static int MAXIMUM_BUFFER_SIZE = 8000000;
 
+    /**
+     * Calculation of centroids for all polygons.
+     * (may affect performance)
+     */
+    public static boolean POLY_CENTROID = false;
+
     /**
      * Optimal placement of labels or symbols on polygons.
      */