[FEATURE] Add follow point alignment for multiline labels

When set to this mode, text alignment for labels will be dependant
on the final placement of the label relative to the point. Eg, if
the label is placed to the left of the point then the label will
be right aligned, and if it is placed to the right of the point
then the label will be left aligned.
(fix #11153)

Author: nyalldawson

python/core/qgspallabeling.sip

@@ -140,7 +140,9 @@ class QgsPalLayerSettings
     {
       MultiLeft,
       MultiCenter,
-      MultiRight
+      MultiRight,
+      MultiFollowPlacement /*< Alignment follows placement of label, eg labels to the left of a feature
+                               will be drawn with right alignment*/
     };
 
     enum ShapeType

src/app/qgslabelinggui.cpp

@@ -141,6 +141,12 @@ QgsLabelingGui::QgsLabelingGui( QgsVectorLayer* layer, QgsMapCanvas* mapCanvas,
       qFatal( "unknown geometry type unexpected" );
   }
 
+  if ( layer->geometryType() == QGis::Point )
+  {
+    // follow placement alignment is only valid for point layers
+    mFontMultiLineAlignComboBox->addItem( tr( "Follow label placement" ) );
+  }
+
   // show/hide options based upon geometry type
   chkMergeLines->setVisible( layer->geometryType() == QGis::Line );
   mDirectSymbolsFrame->setVisible( layer->geometryType() == QGis::Line );
@@ -913,7 +919,7 @@ void QgsLabelingGui::populateDataDefinedButtons( QgsPalLayerSettings& s )
   mFontLineHeightDDBtn->init( mLayer, s.dataDefinedProperty( QgsPalLayerSettings::MultiLineHeight ),
                               QgsDataDefinedButton::AnyType, tr( "double [0.0-10.0]" ) );
   mFontMultiLineAlignDDBtn->init( mLayer, s.dataDefinedProperty( QgsPalLayerSettings::MultiLineAlignment ),
-                                  QgsDataDefinedButton::String, QgsDataDefinedButton::textHorzAlignDesc() );
+                                  QgsDataDefinedButton::String, trString + "[<b>Left</b>|<b>Center</b>|<b>Right</b>|<b>Follow</b>]" );
 
   mDirectSymbDDBtn->init( mLayer, s.dataDefinedProperty( QgsPalLayerSettings::DirSymbDraw ),
                           QgsDataDefinedButton::AnyType, QgsDataDefinedButton::boolDesc() );

src/core/pal/feature.cpp

@@ -275,6 +275,55 @@ namespace pal
     return f->uid;
   }
 
+  LabelPosition::Quadrant FeaturePart::quadrantFromOffset() const
+  {
+    if ( f->quadOffsetX < 0 )
+    {
+      if ( f->quadOffsetY < 0 )
+      {
+        return LabelPosition::QuadrantAboveLeft;
+      }
+      else if ( f->quadOffsetY > 0 )
+      {
+        return LabelPosition::QuadrantBelowLeft;
+      }
+      else
+      {
+        return LabelPosition::QuadrantLeft;
+      }
+    }
+    else  if ( f->quadOffsetX > 0 )
+    {
+      if ( f->quadOffsetY < 0 )
+      {
+        return LabelPosition::QuadrantAboveRight;
+      }
+      else if ( f->quadOffsetY > 0 )
+      {
+        return LabelPosition::QuadrantBelowRight;
+      }
+      else
+      {
+        return LabelPosition::QuadrantRight;
+      }
+    }
+    else
+    {
+      if ( f->quadOffsetY < 0 )
+      {
+        return LabelPosition::QuadrantAbove;
+      }
+      else if ( f->quadOffsetY > 0 )
+      {
+        return LabelPosition::QuadrantBelow;
+      }
+      else
+      {
+        return LabelPosition::QuadrantOver;
+      }
+    }
+  }
+
   int FeaturePart::setPositionOverPoint( double x, double y, double scale, LabelPosition ***lPos, double delta_width, double angle )
   {
     Q_UNUSED( scale );
@@ -322,6 +371,7 @@ namespace pal
       delete lp;
     }
 
+    LabelPosition::Quadrant quadrant = f->quadOffset ? quadrantFromOffset() : LabelPosition::QuadrantOver;
     if ( f->quadOffset )
     {
       if ( f->quadOffsetX != 0 )
@@ -349,7 +399,7 @@ namespace pal
     lx = x + xdiff;
     ly = y + ydiff;
 
-    ( *lPos )[0] = new LabelPosition( id, lx, ly, label_x, label_y, angle, cost, this );
+    ( *lPos )[0] = new LabelPosition( id, lx, ly, label_x, label_y, angle, cost, this, false, quadrant );
     return nbp;
   }
 
@@ -443,6 +493,8 @@ namespace pal
       if ( alpha > a360 )
         alpha -= a360;
 
+      LabelPosition::Quadrant quadrant = LabelPosition::QuadrantOver;
+
       if ( alpha < gamma1 || alpha > a360 - gamma1 )  // on the right
       {
         lx += distlabel;
@@ -452,44 +504,53 @@ namespace pal
 
         //ly += -yrm/2.0 + tan(alpha)*(distlabel + xrm/2);
         ly += -yrm + yrm * iota / ( 2 * gamma1 );
+
+        quadrant = LabelPosition::QuadrantRight;
       }
       else if ( alpha < a90 - gamma2 )  // top-right
       {
         lx += distlabel * cos( alpha );
         ly += distlabel * sin( alpha );
+        quadrant = LabelPosition::QuadrantAboveRight;
       }
       else if ( alpha < a90 + gamma2 ) // top
       {
         //lx += -xrm/2.0 - tan(alpha+a90)*(distlabel + yrm/2);
         lx += -xrm * ( alpha - a90 + gamma2 ) / ( 2 * gamma2 );
         ly += distlabel;
+        quadrant = LabelPosition::QuadrantAbove;
       }
       else if ( alpha < a180 - gamma1 )  // top left
       {
         lx += distlabel * cos( alpha ) - xrm;
         ly += distlabel * sin( alpha );
+        quadrant = LabelPosition::QuadrantAboveLeft;
       }
       else if ( alpha < a180 + gamma1 ) // left
       {
         lx += -distlabel - xrm;
         //ly += -yrm/2.0 - tan(alpha)*(distlabel + xrm/2);
         ly += - ( alpha - a180 + gamma1 ) * yrm / ( 2 * gamma1 );
+        quadrant = LabelPosition::QuadrantLeft;
       }
       else if ( alpha < a270 - gamma2 ) // down - left
       {
         lx += distlabel * cos( alpha ) - xrm;
         ly += distlabel * sin( alpha ) - yrm;
+        quadrant = LabelPosition::QuadrantBelowLeft;
       }
       else if ( alpha < a270 + gamma2 ) // down
       {
         ly += -distlabel - yrm;
         //lx += -xrm/2.0 + tan(alpha+a90)*(distlabel + yrm/2);
         lx += -xrm + ( alpha - a270 + gamma2 ) * xrm / ( 2 * gamma2 );
+        quadrant = LabelPosition::QuadrantBelow;
       }
-      else if ( alpha < a360 )
+      else if ( alpha < a360 ) // down - right
       {
         lx += distlabel * cos( alpha );
         ly += distlabel * sin( alpha ) - yrm;
+        quadrant = LabelPosition::QuadrantBelowRight;
       }
 
       double cost;
@@ -499,7 +560,7 @@ namespace pal
       else
         cost = 0.0001 + 0.0020 * double( icost ) / double( nbp - 1 );
 
-      ( *lPos )[i] = new LabelPosition( i, lx, ly, xrm, yrm, angle, cost, this );
+      ( *lPos )[i] = new LabelPosition( i, lx, ly, xrm, yrm, angle, cost, this, false, quadrant );
 
       icost += inc;
 

src/core/pal/feature.h

@@ -44,7 +44,7 @@
 
 #include "pointset.h"
 #include "util.h"
-
+#include "labelposition.h"
 
 namespace pal
 {
@@ -321,6 +321,9 @@ namespace pal
 
       void addSizePenalty( int nbp, LabelPosition** lPos, double bbx[4], double bby[4] );
 
+    private:
+
+      LabelPosition::Quadrant quadrantFromOffset() const;
   };
 
 } // end namespace pal

src/core/pal/labelposition.cpp

@@ -54,8 +54,9 @@
 
 namespace pal
 {
-  LabelPosition::LabelPosition( int id, double x1, double y1, double w, double h, double alpha, double cost, FeaturePart *feature, bool isReversed )
-      : id( id ), cost( cost ), feature( feature ), probFeat( 0 ), nbOverlap( 0 ), alpha( alpha ), w( w ), h( h ), nextPart( NULL ), partId( -1 ), reversed( isReversed ), upsideDown( false )
+  LabelPosition::LabelPosition( int id, double x1, double y1, double w, double h, double alpha, double cost, FeaturePart *feature, bool isReversed, Quadrant quadrant )
+      : id( id ), cost( cost ), feature( feature ), probFeat( 0 ), nbOverlap( 0 ), alpha( alpha ), w( w ), h( h ), nextPart( NULL ), partId( -1 ), reversed( isReversed ), upsideDown( false ),
+      quadrant( quadrant )
   {
 
     // alpha take his value bw 0 and 2*pi rad
@@ -166,6 +167,7 @@ namespace pal
     partId = other.partId;
     upsideDown = other.upsideDown;
     reversed = other.reversed;
+    quadrant = other.quadrant;
   }
 
   bool LabelPosition::isIn( double *bbox )

src/core/pal/labelposition.h

@@ -48,13 +48,31 @@ namespace pal
 
 
   /**
-   * \brief LabelPositon is a candidate feature label position
+   * \brief LabelPosition is a candidate feature label position
    */
   class CORE_EXPORT LabelPosition
   {
       friend class CostCalculator;
       friend class PolygonCostCalculator;
 
+    public:
+
+      /**
+       * \brief Position of label candidate relative to feature.
+       */
+      enum Quadrant
+      {
+        QuadrantAboveLeft,
+        QuadrantAbove,
+        QuadrantAboveRight,
+        QuadrantLeft,
+        QuadrantOver,
+        QuadrantRight,
+        QuadrantBelowLeft,
+        QuadrantBelow,
+        QuadrantBelowRight
+      };
+
     protected:
 
       int id;
@@ -81,10 +99,13 @@ namespace pal
 
       bool upsideDown;
 
+      LabelPosition::Quadrant quadrant;
+
       bool isInConflictSinglePart( LabelPosition* lp );
       bool isInConflictMultiPart( LabelPosition* lp );
 
     public:
+
       /**
        * \brief create a new LabelPosition
        *
@@ -97,11 +118,12 @@ namespace pal
        * \param cost geographic cost
        * \param feature labelpos owners
        * \param isReversed label is reversed
+       * \param quadrant relative position of label to feature
        */
       LabelPosition( int id, double x1, double y1,
                      double w, double h,
                      double alpha, double cost,
-                     FeaturePart *feature, bool isReversed = false );
+                     FeaturePart *feature, bool isReversed = false, Quadrant quadrant = QuadrantOver );
 
       /** copy constructor */
       LabelPosition( const LabelPosition& other );
@@ -215,6 +237,8 @@ namespace pal
       bool getReversed() const { return reversed; }
       bool getUpsideDown() const { return upsideDown; }
 
+      Quadrant getQuadrant() const { return quadrant; }
+
       void print();
 
       LabelPosition* getNextPart() const { return nextPart; }

src/core/qgspallabeling.cpp

@@ -2720,6 +2720,10 @@ void QgsPalLayerSettings::parseTextFormatting()
       {
         aligntype = QgsPalLayerSettings::MultiRight;
       }
+      else if ( str.compare( "Follow", Qt::CaseInsensitive ) == 0 )
+      {
+        aligntype = QgsPalLayerSettings::MultiFollowPlacement;
+      }
       dataDefinedValues.insert( QgsPalLayerSettings::MultiLineAlignment, QVariant(( int )aligntype ) );
     }
   }
@@ -4038,6 +4042,29 @@ void QgsPalLabeling::drawLabeling( QgsRenderContext& context )
 #endif
     tmpLyr.textFont = dFont;
 
+    if ( tmpLyr.multilineAlign == QgsPalLayerSettings::MultiFollowPlacement )
+    {
+      //calculate font alignment based on label quadrant
+      switch (( *it )->getQuadrant() )
+      {
+        case LabelPosition::QuadrantAboveLeft:
+        case LabelPosition::QuadrantLeft:
+        case LabelPosition::QuadrantBelowLeft:
+          tmpLyr.multilineAlign = QgsPalLayerSettings::MultiRight;
+          break;
+        case LabelPosition::QuadrantAbove:
+        case LabelPosition::QuadrantOver:
+        case LabelPosition::QuadrantBelow:
+          tmpLyr.multilineAlign = QgsPalLayerSettings::MultiCenter;
+          break;
+        case LabelPosition::QuadrantAboveRight:
+        case LabelPosition::QuadrantRight:
+        case LabelPosition::QuadrantBelowRight:
+          tmpLyr.multilineAlign = QgsPalLayerSettings::MultiLeft;
+          break;
+      }
+    }
+
     // update tmpLyr with any data defined text style values
     dataDefinedTextStyle( tmpLyr, ddValues );
 

src/core/qgspallabeling.h

@@ -120,7 +120,9 @@ class CORE_EXPORT QgsPalLayerSettings
     {
       MultiLeft = 0,
       MultiCenter,
-      MultiRight
+      MultiRight,
+      MultiFollowPlacement /*< Alignment follows placement of label, eg labels to the left of a feature
+                               will be drawn with right alignment*/
     };
 
     enum ShapeType