Improve polygon perimeter labeling

nyalldawson · nyalldawson · commit 4e41f1a79a5c · 2016-08-10T08:09:02.000+10:00
This commit changes the way polygon perimeter labeling works. Previously the polygon would be clipped to the view extent, and then the boundary of the clipped polygon used for perimeter labeling. This tended to push the labels to the outside of the map extent (the clip boundary), since that's the longest straight section of the resultant geometry. Now, the boundary is taken *before* the clip, so that perimeter based labels will never be placed on the artificial boundary created at the map's extent. (cherry-picked from 27697e6)
diff --git a/src/core/qgspallabeling.cpp b/src/core/qgspallabeling.cpp
@@ -2442,6 +2442,16 @@ void QgsPalLayerSettings::registerFeature( QgsFeature& f, QgsRenderContext &cont
     }
   }
 
+  // if using perimeter based labeling for polygons, get the polygon's
+  // linear boundary and use that for the label geometry
+  if (( geom->type() == QGis::Polygon )
+      && ( placement == Line || placement == PerimeterCurved ) )
+  {
+    QgsGeometry* boundaryGeom = new QgsGeometry( geom->geometry()->boundary() );
+    geom = boundaryGeom;
+    scopedClonedGeom.reset( boundaryGeom );
+  }
+
   // whether we're going to create a centroid for polygon
   bool centroidPoly = (( placement == QgsPalLayerSettings::AroundPoint
                          || placement == QgsPalLayerSettings::OverPoint )
@@ -2461,6 +2471,7 @@ void QgsPalLayerSettings::registerFeature( QgsFeature& f, QgsRenderContext &cont
   if ( QgsPalLabeling::geometryRequiresPreparation( geom, context, ct, doClip ? extentGeom : nullptr ) )
   {
     scopedPreparedGeom.reset( QgsPalLabeling::prepareGeometry( geom, context, ct, doClip ? extentGeom : nullptr ) );
+
     if ( !scopedPreparedGeom.data() )
       return;
     preparedGeom = scopedPreparedGeom.data();
@@ -2516,16 +2527,7 @@ void QgsPalLayerSettings::registerFeature( QgsFeature& f, QgsRenderContext &cont
     }
   }
 
-  GEOSGeometry* geos_geom_clone;
-  GEOSGeomTypes geomType = ( GEOSGeomTypes ) GEOSGeomTypeId_r( QgsGeometry::getGEOSHandler(), geos_geom );
-  if (( geomType == GEOS_POLYGON || geomType == GEOS_MULTIPOLYGON ) && repeatDistance > 0 && ( placement == Line || placement == PerimeterCurved ) )
-  {
-    geos_geom_clone = GEOSBoundary_r( QgsGeometry::getGEOSHandler(), geos_geom );
-  }
-  else
-  {
-    geos_geom_clone = GEOSGeom_clone_r( QgsGeometry::getGEOSHandler(), geos_geom );
-  }
+  GEOSGeometry* geos_geom_clone = GEOSGeom_clone_r( QgsGeometry::getGEOSHandler(), geos_geom );
   GEOSGeometry* geosObstacleGeomClone = nullptr;
   if ( geosObstacleGeom )
   {
