[FEATURE] add grid renderer for points displacement. funded by Kartoza

python/core/symbology/qgspointdisplacementrenderer.sip

@@ -23,7 +23,8 @@ class QgsPointDisplacementRenderer: QgsPointDistanceRenderer
     enum Placement
     {
       Ring,
-      ConcentricRings
+      ConcentricRings,
+      Grid
     };
 
     QgsPointDisplacementRenderer( const QString &labelAttributeName = QString() );

src/core/symbology/qgspointdisplacementrenderer.cpp

@@ -75,11 +75,17 @@ void QgsPointDisplacementRenderer::drawGroup( QPointF centerPoint, QgsRenderCont
   QList<QPointF> symbolPositions;
   QList<QPointF> labelPositions;
   double circleRadius = -1.0;
-  calculateSymbolAndLabelPositions( symbolContext, centerPoint, group.size(), diagonal, symbolPositions, labelPositions, circleRadius );
+  double gridRadius;
+  int gridSize;
+
+  calculateSymbolAndLabelPositions( symbolContext, centerPoint, group.size(), diagonal, symbolPositions, labelPositions, circleRadius, gridRadius, gridSize );
 
   //draw circle
   if ( circleRadius > 0 )
     drawCircle( circleRadius, symbolContext, centerPoint, group.size() );
+  //draw grid
+  else
+    drawGrid( gridSize, symbolContext, symbolPositions, group.size() );
 
   if ( group.size() > 1 )
   {
@@ -221,7 +227,8 @@ void QgsPointDisplacementRenderer::setCenterSymbol( QgsMarkerSymbol *symbol )
 }
 
 void QgsPointDisplacementRenderer::calculateSymbolAndLabelPositions( QgsSymbolRenderContext &symbolContext, QPointF centerPoint, int nPosition,
-    double symbolDiagonal, QList<QPointF> &symbolPositions, QList<QPointF> &labelShifts, double &circleRadius ) const
+    double symbolDiagonal, QList<QPointF> &symbolPositions, QList<QPointF> &labelShifts, double &circleRadius, double &gridRadius,
+    int &gridSize ) const
 {
   symbolPositions.clear();
   labelShifts.clear();
@@ -294,6 +301,75 @@ void QgsPointDisplacementRenderer::calculateSymbolAndLabelPositions( QgsSymbolRe
       }
       break;
     }
+    case Grid:
+    {
+      double centerDiagonal = symbolContext.renderContext().convertToPainterUnits( M_SQRT2 * mCenterSymbol->size(),
+                              mCenterSymbol->sizeUnit(), mCenterSymbol->sizeMapUnitScale() );
+      int pointsRemaining = nPosition;
+      gridSize = ceil( sqrt( pointsRemaining ) );
+      if ( pointsRemaining - pow( gridSize - 1, 2 ) < gridSize )
+        gridSize -= 1;
+      double originalPointRadius = ( ( centerDiagonal / 2.0 + symbolDiagonal / 2.0 ) + symbolDiagonal ) / 2;
+      double userPointRadius =  originalPointRadius + circleAdditionPainterUnits;
+
+      int yIndex = 0;
+      while ( pointsRemaining > 0 )
+      {
+        for ( int xIndex = 0; xIndex < gridSize && pointsRemaining > 0; ++xIndex )
+        {
+          QPointF positionShift( userPointRadius * xIndex, userPointRadius * yIndex );
+          QPointF labelShift( ( userPointRadius + symbolDiagonal / 2 ) * xIndex, ( userPointRadius + symbolDiagonal / 2 ) * yIndex );
+          symbolPositions.append( centerPoint + positionShift );
+          labelShifts.append( labelShift );
+          pointsRemaining--;
+        }
+        yIndex++;
+      }
+
+      centralizeGrid( symbolPositions, userPointRadius, gridSize );
+      centralizeGrid( labelShifts, userPointRadius, gridSize );
+      gridRadius = userPointRadius;
+      break;
+    }
+  }
+}
+
+void QgsPointDisplacementRenderer::centralizeGrid( QList<QPointF> &pointSymbolPositions, double radius, int size ) const
+{
+  double shiftAmount = -radius * ( size - 1 ) / 2;
+  QPointF centralShift( shiftAmount, shiftAmount );
+  for ( int i = 0; i < pointSymbolPositions.size(); ++i )
+  {
+    pointSymbolPositions[i] += centralShift;
+  }
+}
+
+void QgsPointDisplacementRenderer::drawGrid( int gridSizeUnits, QgsSymbolRenderContext &context,
+    QList<QPointF> pointSymbolPositions, int nSymbols )
+{
+  QPainter *p = context.renderContext().painter();
+  if ( nSymbols < 2 || !p ) //draw grid only if multiple features
+  {
+    return;
+  }
+
+  QPen gridPen( mCircleColor );
+  gridPen.setWidthF( context.outputLineWidth( mCircleWidth ) );
+  p->setPen( gridPen );
+
+  for ( int i = 0; i < pointSymbolPositions.size(); ++i )
+  {
+    if ( i + 1 < pointSymbolPositions.size() && 0 != ( i + 1 ) % gridSizeUnits )
+    {
+      QLineF gridLineRow( pointSymbolPositions[i], pointSymbolPositions[i + 1] );
+      p->drawLine( gridLineRow );
+    }
+
+    if ( i + gridSizeUnits < pointSymbolPositions.size() )
+    {
+      QLineF gridLineColumn( pointSymbolPositions[i], pointSymbolPositions[i + gridSizeUnits] );
+      p->drawLine( gridLineColumn );
+    }
   }
 }
 

src/core/symbology/qgspointdisplacementrenderer.h

@@ -37,7 +37,8 @@ class CORE_EXPORT QgsPointDisplacementRenderer: public QgsPointDistanceRenderer
     enum Placement
     {
       Ring, //!< Place points in a single ring around group
-      ConcentricRings //!< Place points in concentric rings around group
+      ConcentricRings, //!< Place points in concentric rings around group
+      Grid //!< Place points in a grid around group
     };
 
     /**
@@ -155,9 +156,13 @@ class CORE_EXPORT QgsPointDisplacementRenderer: public QgsPointDistanceRenderer
     virtual void drawGroup( QPointF centerPoint, QgsRenderContext &context, const QgsPointDistanceRenderer::ClusteredGroup &group ) override SIP_FORCE;
 
     //helper functions
-    void calculateSymbolAndLabelPositions( QgsSymbolRenderContext &symbolContext, QPointF centerPoint, int nPosition, double symbolDiagonal, QList<QPointF> &symbolPositions, QList<QPointF> &labelShifts, double &circleRadius ) const;
+    void calculateSymbolAndLabelPositions( QgsSymbolRenderContext &symbolContext, QPointF centerPoint, int nPosition, double symbolDiagonal, QList<QPointF> &symbolPositions, QList<QPointF> &labelShifts, double &circleRadius,
+                                           double &gridRadius, int &gridSize ) const;
     void drawCircle( double radiusPainterUnits, QgsSymbolRenderContext &context, QPointF centerPoint, int nSymbols );
     void drawSymbols( const ClusteredGroup &group, QgsRenderContext &context, const QList<QPointF> &symbolPositions );
+    void drawGrid( int gridSizeUnits, QgsSymbolRenderContext &context,
+                   QList<QPointF> pointSymbolPositions, int nSymbols );
+    void centralizeGrid( QList<QPointF> &pointSymbolPositions, double radius, int size ) const;
 };
 
 #endif // QGSPOINTDISPLACEMENTRENDERER_H

src/gui/symbology/qgspointdisplacementrendererwidget.cpp

@@ -79,6 +79,7 @@ QgsPointDisplacementRendererWidget::QgsPointDisplacementRendererWidget( QgsVecto
 
   mPlacementComboBox->addItem( tr( "Ring" ), QgsPointDisplacementRenderer::Ring );
   mPlacementComboBox->addItem( tr( "Concentric rings" ), QgsPointDisplacementRenderer::ConcentricRings );
+  mPlacementComboBox->addItem( tr( "Grid" ), QgsPointDisplacementRenderer::Grid );
 
   //insert attributes into combo box
   if ( layer )

src/ui/qgspointdisplacementrendererwidgetbase.ui

@@ -215,7 +215,7 @@
       <item row="3" column="0">
        <widget class="QLabel" name="mCircleRadiusLabel">
         <property name="text">
-         <string>Ring size adjustment</string>
+         <string>Size adjustment</string>
         </property>
        </widget>
       </item>