Disable "merge lines" option with "line direction symbol"

This sometimes produces inversed lines and therefore unreliable results.

Author: m-kuhn

src/app/qgslabelinggui.cpp

@@ -853,6 +853,16 @@ void QgsLabelingGui::updateUi()
   syncDefinedCheckboxFrame( mFormatNumDDBtn, mFormatNumChkBx, mFormatNumFrame );
   syncDefinedCheckboxFrame( mScaleBasedVisibilityDDBtn, mScaleBasedVisibilityChkBx, mScaleBasedVisibilityFrame );
   syncDefinedCheckboxFrame( mFontLimitPixelDDBtn, mFontLimitPixelChkBox, mFontLimitPixelFrame );
+
+  chkMergeLines->setEnabled( !mDirectSymbChkBx->isChecked() );
+  if ( mDirectSymbChkBx->isChecked() )
+  {
+    chkMergeLines->setToolTip( tr( "This option is not compatible with line direction symbols." ) );
+  }
+  else
+  {
+    chkMergeLines->setToolTip( QString() );
+  }
 }
 
 

src/core/qgspallabeling.cpp

@@ -351,7 +351,7 @@ QgsPalLayerSettings& QgsPalLayerSettings::operator=( const QgsPalLayerSettings &
   upsidedownLabels = s.upsidedownLabels;
 
   labelPerPart = s.labelPerPart;
-  mergeLines = s.mergeLines;
+  mergeLines = s.mergeLines && !s.addDirectionSymbol;
   minFeatureSize = s.minFeatureSize;
   limitNumLabels = s.limitNumLabels;
   maxNumLabels = s.maxNumLabels;

src/core/qgsvectorlayerlabelprovider.cpp

@@ -83,11 +83,17 @@ void QgsVectorLayerLabelProvider::init()
   mPlacement = mSettings.placement;
   mLinePlacementFlags = mSettings.placementFlags;
   mFlags = Flags();
-  if ( mSettings.drawLabels ) mFlags |= DrawLabels;
-  if ( mSettings.displayAll ) mFlags |= DrawAllLabels;
-  if ( mSettings.mergeLines ) mFlags |= MergeConnectedLines;
-  if ( mSettings.centroidInside ) mFlags |= CentroidMustBeInside;
-  if ( mSettings.labelPerPart ) mFlags |= LabelPerFeaturePart;
+  if ( mSettings.drawLabels )
+    mFlags |= DrawLabels;
+  if ( mSettings.displayAll )
+    mFlags |= DrawAllLabels;
+  if ( mSettings.mergeLines && !mSettings.addDirectionSymbol )
+    mFlags |= MergeConnectedLines;
+  if ( mSettings.centroidInside )
+    mFlags |= CentroidMustBeInside;
+  if ( mSettings.labelPerPart )
+    mFlags |= LabelPerFeaturePart;
+
   mPriority = 1 - mSettings.priority / 10.0; // convert 0..10 --> 1..0
 
   if ( mLayerGeometryType == QgsWkbTypes::PointGeometry && mRenderer )