[pal] Consider all label parts when checking polygon obstacle cost

Fixes curved label candidates not being marked as in conflict with
polygon obstacles when letters other than the first letter conflict
with the polygon.

src/core/pal/labelposition.cpp

@@ -305,6 +305,14 @@ namespace pal
     return false; // no conflict found
   }
 
+  int LabelPosition::partCount() const
+  {
+    if ( nextPart )
+      return nextPart->partCount() + 1;
+    else
+      return 1;
+  }
+
   void LabelPosition::offsetPosition( double xOffset, double yOffset )
   {
     for ( int i = 0; i < 4; i++ )
@@ -574,6 +582,14 @@ namespace pal
   }
 
   int LabelPosition::polygonIntersectionCost( PointSet *polygon ) const
+  {
+    //effectively take the average polygon intersection cost for all label parts
+    double totalCost = polygonIntersectionCostForParts( polygon );
+    int n = partCount();
+    return ceil( totalCost / n );
+  }
+
+  double LabelPosition::polygonIntersectionCostForParts( PointSet *polygon ) const
   {
     if ( !mGeos )
       createGeosGeom();
@@ -583,7 +599,7 @@ namespace pal
 
     GEOSContextHandle_t geosctxt = geosContext();
 
-    int cost = 0;
+    double cost = 0;
     //check the label center. if covered by polygon, initial cost of 4
     if ( polygon->containsPoint(( x[0] + x[2] ) / 2.0, ( y[0] + y[2] ) / 2.0 ) )
       cost += 4;
@@ -592,33 +608,32 @@ namespace pal
     {
       //calculate proportion of label candidate which is covered by polygon
       GEOSGeometry* intersectionGeom = GEOSIntersection_r( geosctxt, mGeos, polygon->mGeos );
-      if ( !intersectionGeom )
-        return cost;
-
-      double positionArea = 0;
-      if ( GEOSArea_r( geosctxt, mGeos, &positionArea ) != 1 )
+      if ( intersectionGeom )
       {
+        double positionArea = 0;
+        if ( GEOSArea_r( geosctxt, mGeos, &positionArea ) == 1 )
+        {
+          double intersectionArea = 0;
+          if ( GEOSArea_r( geosctxt, intersectionGeom, &intersectionArea ) == 1 )
+          {
+            double portionCovered = intersectionArea / positionArea;
+            cost += portionCovered * 8.0; //cost of 8 if totally covered
+          }
+        }
         GEOSGeom_destroy_r( geosctxt, intersectionGeom );
-        return cost;
       }
-
-      double intersectionArea = 0;
-      if ( GEOSArea_r( geosctxt, intersectionGeom, &intersectionArea ) != 1 )
-      {
-        intersectionArea = 0;
-      }
-
-      GEOSGeom_destroy_r( geosctxt, intersectionGeom );
-
-      double portionCovered = intersectionArea / positionArea;
-      cost += ceil( portionCovered * 8.0 ); //cost of 8 if totally covered
-      return cost;
     }
     catch ( GEOSException &e )
     {
       QgsMessageLog::logMessage( QObject::tr( "Exception: %1" ).arg( e.what() ), QObject::tr( "GEOS" ) );
-      return cost;
     }
+
+    if ( nextPart )
+    {
+      cost += nextPart->polygonIntersectionCostForParts( polygon );
+    }
+
+    return cost;
   }
 
 } // end namespace

src/core/pal/labelposition.h

@@ -299,6 +299,15 @@ namespace pal
       double mCost;
       bool mHasObstacleConflict;
 
+      /** Calculates the total number of parts for this label position
+       */
+      int partCount() const;
+
+      /** Calculates the polygon intersection cost for a single label position part
+       * @returns double between 0 - 12
+       */
+      double polygonIntersectionCostForParts( PointSet* polygon ) const;
+
   };
 
 } // end namespace