[labeling] Fix curved labels sometimes placed below line even when

set to above line only

src/core/pal/feature.cpp

@@ -998,22 +998,31 @@ LabelPosition *FeaturePart::curvedPlacementAtOffset( PointSet *path_positions, d
     double _distance = offsetAlongSegment;
     int endindex = index;
 
+    double startLabelX = 0;
+    double startLabelY = 0;
+    double endLabelX = 0;
+    double endLabelY = 0;
     for ( int i = 0; i < li->char_num; i++ )
     {
       LabelInfo::CharacterInfo &ci = li->char_info[i];
-      double start_x, start_y, end_x, end_y;
-      if ( !nextCharPosition( ci.width, path_distances[endindex], path_positions, endindex, _distance, start_x, start_y, end_x, end_y ) )
+      double start_x, start_y;
+      if ( !nextCharPosition( ci.width, path_distances[endindex], path_positions, endindex, _distance, start_x, start_y, endLabelX, endLabelY ) )
       {
         return nullptr;
       }
+      if ( i == 0 )
+      {
+        startLabelX = start_x;
+        startLabelY = start_y;
+      }
     }
 
     // Determine the angle of the path segment under consideration
-    double dx = path_positions->x[endindex] - path_positions->x[index];
-    double dy = path_positions->y[endindex] - path_positions->y[index];
-    double line_angle = std::atan2( -dy, dx );
+    double dx = endLabelX - startLabelX;
+    double dy = endLabelY - startLabelY;
+    const double lineAngle = std::atan2( -dy, dx ) * 180 / M_PI;
 
-    bool isRightToLeft = ( line_angle > 0.55 * M_PI || line_angle < -0.45 * M_PI );
+    bool isRightToLeft = ( lineAngle > 90 || lineAngle < -90 );
     reversed = isRightToLeft;
     orientation = isRightToLeft ? -1 : 1;
   }
@@ -1175,7 +1184,7 @@ int FeaturePart::createCurvedCandidatesAlongLine( QList< LabelPosition * > &lPos
   QLinkedList<LabelPosition *> positions;
   double delta = std::max( li->label_height, total_distance / mLF->layer()->pal->line_p );
 
-  unsigned long flags = mLF->layer()->arrangementFlags();
+  pal::LineArrangementFlags flags = mLF->layer()->arrangementFlags();
   if ( flags == 0 )
     flags = FLAG_ON_LINE; // default flag
 

tests/src/core/testqgslabelingengine.cpp

@@ -56,6 +56,7 @@ class TestQgsLabelingEngine : public QObject
     void testTouchingParts();
     void testMergingLinesWithForks();
     void testCurvedLabelsWithTinySegments();
+    void testCurvedLabelCorrectLinePlacement();
     void testLabelBoundary();
     void testLabelBlockingRegion();
     void testLabelRotationWithReprojection();
@@ -1037,6 +1038,72 @@ void TestQgsLabelingEngine::testCurvedLabelsWithTinySegments()
   QVERIFY( imageCheck( QStringLiteral( "label_curved_label_small_segments" ), img, 20 ) );
 }
 
+void TestQgsLabelingEngine::testCurvedLabelCorrectLinePlacement()
+{
+  // test drawing curved labels when input linestring has many small segments
+  QgsPalLayerSettings settings;
+  setDefaultLabelParams( settings );
+
+  QgsTextFormat format = settings.format();
+  format.setSize( 20 );
+  format.setColor( QColor( 0, 0, 0 ) );
+  settings.setFormat( format );
+
+  settings.fieldName = QStringLiteral( "'XXXXXXXXXXXXXXXXXXXXXXXXXX'" );
+  settings.isExpression = true;
+  settings.placement = QgsPalLayerSettings::Curved;
+  settings.placementFlags = QgsPalLayerSettings::AboveLine | QgsPalLayerSettings::MapOrientation;
+  settings.maxCurvedCharAngleIn = 99;
+  settings.maxCurvedCharAngleOut = 99;
+
+  std::unique_ptr< QgsVectorLayer> vl2( new QgsVectorLayer( QStringLiteral( "LineString?crs=epsg:4326&field=id:integer" ), QStringLiteral( "vl" ), QStringLiteral( "memory" ) ) );
+  vl2->setRenderer( new QgsNullSymbolRenderer() );
+
+  QgsFeature f;
+  f.setAttributes( QgsAttributes() << 1 );
+  // Geometry which roughly curves around from "1 oclock" anticlockwise to 6 oclock.
+  QgsGeometry g( QgsGeometry::fromWkt( QStringLiteral( "LineString (0.30541596873255172 0.3835845896147404, -0.08989391401451696 0.21831379117811278, -0.33668341708542704 -0.01619207146845336, -0.156895589056393 -0.20714684533780003, 0.02735901730876611 -0.21496370742601911)" ) ) );
+  f.setGeometry( g );
+  QVERIFY( vl2->dataProvider()->addFeature( f ) );
+
+  vl2->setLabeling( new QgsVectorLayerSimpleLabeling( settings ) );  // TODO: this should not be necessary!
+  vl2->setLabelsEnabled( true );
+
+  // make a fake render context
+  QSize size( 640, 480 );
+  QgsMapSettings mapSettings;
+  mapSettings.setDestinationCrs( vl2->crs() );
+
+  mapSettings.setOutputSize( size );
+  mapSettings.setExtent( g.boundingBox() );
+  mapSettings.setLayers( QList<QgsMapLayer *>() << vl2.get() );
+  mapSettings.setOutputDpi( 96 );
+
+  QgsLabelingEngineSettings engineSettings = mapSettings.labelingEngineSettings();
+  engineSettings.setFlag( QgsLabelingEngineSettings::UsePartialCandidates, false );
+  engineSettings.setFlag( QgsLabelingEngineSettings::DrawLabelRectOnly, true );
+  //engineSettings.setFlag( QgsLabelingEngineSettings::DrawCandidates, true );
+  mapSettings.setLabelingEngineSettings( engineSettings );
+
+  QgsMapRendererSequentialJob job( mapSettings );
+  job.start();
+  job.waitForFinished();
+
+  QImage img = job.renderedImage();
+  QVERIFY( imageCheck( QStringLiteral( "label_curved_label_above_1" ), img, 20 ) );
+
+  // and below...
+  settings.placementFlags = QgsPalLayerSettings::BelowLine | QgsPalLayerSettings::MapOrientation;
+  vl2->setLabeling( new QgsVectorLayerSimpleLabeling( settings ) );  // TODO: this should not be necessary!
+
+  QgsMapRendererSequentialJob job2( mapSettings );
+  job2.start();
+  job2.waitForFinished();
+
+  img = job2.renderedImage();
+  QVERIFY( imageCheck( QStringLiteral( "label_curved_label_below_1" ), img, 20 ) );
+}
+
 void TestQgsLabelingEngine::testLabelBoundary()
 {
   // test that no labels are drawn outside of the specified label boundary