Fix artifacts when rendering filled line symbol

python/PyQt6/core/auto_additions/qgssymbollayerutils.py

@@ -22,6 +22,8 @@
     QgsSymbolLayerUtils.decodeBrushStyle = staticmethod(QgsSymbolLayerUtils.decodeBrushStyle)
     QgsSymbolLayerUtils.encodeSldBrushStyle = staticmethod(QgsSymbolLayerUtils.encodeSldBrushStyle)
     QgsSymbolLayerUtils.decodeSldBrushStyle = staticmethod(QgsSymbolLayerUtils.decodeSldBrushStyle)
+    QgsSymbolLayerUtils.penCapStyleToEndCapStyle = staticmethod(QgsSymbolLayerUtils.penCapStyleToEndCapStyle)
+    QgsSymbolLayerUtils.penJoinStyleToJoinStyle = staticmethod(QgsSymbolLayerUtils.penJoinStyleToJoinStyle)
     QgsSymbolLayerUtils.hasSldSymbolizer = staticmethod(QgsSymbolLayerUtils.hasSldSymbolizer)
     QgsSymbolLayerUtils.decodeCoordinateReference = staticmethod(QgsSymbolLayerUtils.decodeCoordinateReference)
     QgsSymbolLayerUtils.encodeCoordinateReference = staticmethod(QgsSymbolLayerUtils.encodeCoordinateReference)

python/PyQt6/core/auto_generated/geometry/qgsgeos.sip.in

@@ -106,6 +106,8 @@ Curved geometries are not supported.
 
     virtual QgsAbstractGeometry *buffer( double distance, int segments, Qgis::EndCapStyle endCapStyle, Qgis::JoinStyle joinStyle, double miterLimit, QString *errorMsg = 0 ) const;
 
+
+
     virtual QgsAbstractGeometry *simplify( double tolerance, QString *errorMsg = 0 ) const;
 
     virtual QgsAbstractGeometry *interpolate( double distance, QString *errorMsg = 0 ) const;
@@ -287,6 +289,7 @@ This method requires a QGIS build based on GEOS 3.7 or later.
                                          QgsPointSequence &topologyTestPoints,
                                          QString *errorMsg = 0, bool skipIntersectionCheck = false ) const;
 
+
     virtual QgsAbstractGeometry *offsetCurve( double distance, int segments, Qgis::JoinStyle joinStyle, double miterLimit, QString *errorMsg = 0 ) const;
 
 

python/PyQt6/core/auto_generated/symbology/qgssymbollayerutils.sip.in

@@ -60,6 +60,20 @@ Contains utility functions for working with symbols and symbol layers.
     static QString encodeSldBrushStyle( Qt::BrushStyle style );
     static Qt::BrushStyle decodeSldBrushStyle( const QString &str );
 
+    static Qgis::EndCapStyle penCapStyleToEndCapStyle( Qt::PenCapStyle style );
+%Docstring
+Converts a Qt pen cap style to a QGIS end cap style.
+
+.. versionadded:: 3.42
+%End
+
+    static Qgis::JoinStyle penJoinStyleToJoinStyle( Qt::PenJoinStyle style );
+%Docstring
+Converts a Qt pen joinstyle to a QGIS join style.
+
+.. versionadded:: 3.42
+%End
+
     static bool hasSldSymbolizer( const QDomElement &element );
 %Docstring
 Returns ``True`` if a DOM ``element`` contains an SLD Symbolizer element.
@@ -814,6 +828,15 @@ how the geometry should be drawn for a symbol of the given ``type``,
 as a list of geometry parts and rings.
 
 .. versionadded:: 3.40
+%End
+
+    static QList< QList< QPolygonF > > toQPolygonF( const QgsAbstractGeometry *geometry, Qgis::SymbolType type );
+%Docstring
+Converts a ``geometry`` to a set of QPolygonF objects representing
+how the geometry should be drawn for a symbol of the given ``type``,
+as a list of geometry parts and rings.
+
+.. versionadded:: 3.42
 %End
 
     static QPointF polygonCentroid( const QPolygonF &points );

python/core/auto_additions/qgssymbollayerutils.py

@@ -22,6 +22,8 @@
     QgsSymbolLayerUtils.decodeBrushStyle = staticmethod(QgsSymbolLayerUtils.decodeBrushStyle)
     QgsSymbolLayerUtils.encodeSldBrushStyle = staticmethod(QgsSymbolLayerUtils.encodeSldBrushStyle)
     QgsSymbolLayerUtils.decodeSldBrushStyle = staticmethod(QgsSymbolLayerUtils.decodeSldBrushStyle)
+    QgsSymbolLayerUtils.penCapStyleToEndCapStyle = staticmethod(QgsSymbolLayerUtils.penCapStyleToEndCapStyle)
+    QgsSymbolLayerUtils.penJoinStyleToJoinStyle = staticmethod(QgsSymbolLayerUtils.penJoinStyleToJoinStyle)
     QgsSymbolLayerUtils.hasSldSymbolizer = staticmethod(QgsSymbolLayerUtils.hasSldSymbolizer)
     QgsSymbolLayerUtils.decodeCoordinateReference = staticmethod(QgsSymbolLayerUtils.decodeCoordinateReference)
     QgsSymbolLayerUtils.encodeCoordinateReference = staticmethod(QgsSymbolLayerUtils.encodeCoordinateReference)

python/core/auto_generated/geometry/qgsgeos.sip.in

@@ -106,6 +106,8 @@ Curved geometries are not supported.
 
     virtual QgsAbstractGeometry *buffer( double distance, int segments, Qgis::EndCapStyle endCapStyle, Qgis::JoinStyle joinStyle, double miterLimit, QString *errorMsg = 0 ) const;
 
+
+
     virtual QgsAbstractGeometry *simplify( double tolerance, QString *errorMsg = 0 ) const;
 
     virtual QgsAbstractGeometry *interpolate( double distance, QString *errorMsg = 0 ) const;
@@ -287,6 +289,7 @@ This method requires a QGIS build based on GEOS 3.7 or later.
                                          QgsPointSequence &topologyTestPoints,
                                          QString *errorMsg = 0, bool skipIntersectionCheck = false ) const;
 
+
     virtual QgsAbstractGeometry *offsetCurve( double distance, int segments, Qgis::JoinStyle joinStyle, double miterLimit, QString *errorMsg = 0 ) const;
 
 

python/core/auto_generated/symbology/qgssymbollayerutils.sip.in

@@ -60,6 +60,20 @@ Contains utility functions for working with symbols and symbol layers.
     static QString encodeSldBrushStyle( Qt::BrushStyle style );
     static Qt::BrushStyle decodeSldBrushStyle( const QString &str );
 
+    static Qgis::EndCapStyle penCapStyleToEndCapStyle( Qt::PenCapStyle style );
+%Docstring
+Converts a Qt pen cap style to a QGIS end cap style.
+
+.. versionadded:: 3.42
+%End
+
+    static Qgis::JoinStyle penJoinStyleToJoinStyle( Qt::PenJoinStyle style );
+%Docstring
+Converts a Qt pen joinstyle to a QGIS join style.
+
+.. versionadded:: 3.42
+%End
+
     static bool hasSldSymbolizer( const QDomElement &element );
 %Docstring
 Returns ``True`` if a DOM ``element`` contains an SLD Symbolizer element.
@@ -814,6 +828,15 @@ how the geometry should be drawn for a symbol of the given ``type``,
 as a list of geometry parts and rings.
 
 .. versionadded:: 3.40
+%End
+
+    static QList< QList< QPolygonF > > toQPolygonF( const QgsAbstractGeometry *geometry, Qgis::SymbolType type );
+%Docstring
+Converts a ``geometry`` to a set of QPolygonF objects representing
+how the geometry should be drawn for a symbol of the given ``type``,
+as a list of geometry parts and rings.
+
+.. versionadded:: 3.42
 %End
 
     static QPointF polygonCentroid( const QPolygonF &points );

src/core/geometry/qgsgeos.cpp

@@ -2094,18 +2094,24 @@ QgsAbstractGeometry *QgsGeos::buffer( double distance, int segments, QString *er
 
 QgsAbstractGeometry *QgsGeos::buffer( double distance, int segments, Qgis::EndCapStyle endCapStyle, Qgis::JoinStyle joinStyle, double miterLimit, QString *errorMsg ) const
 {
-  if ( !mGeos )
+  geos::unique_ptr geos = buffer( mGeos.get(), distance, segments, endCapStyle, joinStyle, miterLimit, errorMsg );
+  return fromGeos( geos.get() ).release();
+}
+
+geos::unique_ptr QgsGeos::buffer( const GEOSGeometry *geometry, double distance, int segments, Qgis::EndCapStyle endCapStyle, Qgis::JoinStyle joinStyle, double miterLimit, QString *errorMsg )
+{
+  if ( !geometry )
   {
     return nullptr;
   }
 
   geos::unique_ptr geos;
   try
   {
-    geos.reset( GEOSBufferWithStyle_r( QgsGeosContext::get(), mGeos.get(), distance, segments, static_cast< int >( endCapStyle ), static_cast< int >( joinStyle ), miterLimit ) );
+    geos.reset( GEOSBufferWithStyle_r( QgsGeosContext::get(), geometry, distance, segments, static_cast< int >( endCapStyle ), static_cast< int >( joinStyle ), miterLimit ) );
   }
   CATCH_GEOS_WITH_ERRMSG( nullptr )
-  return fromGeos( geos.get() ).release();
+  return geos;
 }
 
 QgsAbstractGeometry *QgsGeos::simplify( double tolerance, QString *errorMsg ) const
@@ -2743,9 +2749,9 @@ geos::unique_ptr QgsGeos::createGeosPolygon( const QgsAbstractGeometry *poly, do
   return geosPolygon;
 }
 
-QgsAbstractGeometry *QgsGeos::offsetCurve( double distance, int segments, Qgis::JoinStyle joinStyle, double miterLimit, QString *errorMsg ) const
+geos::unique_ptr QgsGeos::offsetCurve( const GEOSGeometry *geometry, double distance, int segments, Qgis::JoinStyle joinStyle, double miterLimit, QString *errorMsg )
 {
-  if ( !mGeos )
+  if ( !geometry )
     return nullptr;
 
   geos::unique_ptr offset;
@@ -2755,11 +2761,19 @@ QgsAbstractGeometry *QgsGeos::offsetCurve( double distance, int segments, Qgis::
     // https://github.com/qgis/QGIS/issues/53165#issuecomment-1563470832
     if ( segments < 8 )
       segments = 8;
-    offset.reset( GEOSOffsetCurve_r( QgsGeosContext::get(), mGeos.get(), distance, segments, static_cast< int >( joinStyle ), miterLimit ) );
+    offset.reset( GEOSOffsetCurve_r( QgsGeosContext::get(), geometry, distance, segments, static_cast< int >( joinStyle ), miterLimit ) );
   }
   CATCH_GEOS_WITH_ERRMSG( nullptr )
-  std::unique_ptr< QgsAbstractGeometry > offsetGeom = fromGeos( offset.get() );
-  return offsetGeom.release();
+  return offset;
+}
+
+QgsAbstractGeometry *QgsGeos::offsetCurve( double distance, int segments, Qgis::JoinStyle joinStyle, double miterLimit, QString *errorMsg ) const
+{
+  geos::unique_ptr res = offsetCurve( mGeos.get(), distance, segments, joinStyle, miterLimit, errorMsg );
+  if ( !res )
+    return nullptr;
+
+  return fromGeos( res.get() ).release();
 }
 
 std::unique_ptr<QgsAbstractGeometry> QgsGeos::singleSidedBuffer( double distance, int segments, Qgis::BufferSide side, Qgis::JoinStyle joinStyle, double miterLimit, QString *errorMsg ) const

src/core/geometry/qgsgeos.h

@@ -226,6 +226,15 @@ class CORE_EXPORT QgsGeos: public QgsGeometryEngine
     QgsAbstractGeometry *symDifference( const QgsAbstractGeometry *geom, QString *errorMsg = nullptr, const QgsGeometryParameters &parameters = QgsGeometryParameters() ) const override;
     QgsAbstractGeometry *buffer( double distance, int segments, QString *errorMsg = nullptr ) const override;
     QgsAbstractGeometry *buffer( double distance, int segments, Qgis::EndCapStyle endCapStyle, Qgis::JoinStyle joinStyle, double miterLimit, QString *errorMsg = nullptr ) const override;
+
+    /**
+     * Directly calculates the buffer for a GEOS geometry object and returns a GEOS geometry result.
+     *
+     * \note Not available in Python bindings
+     * \since QGIS 3.42
+     */
+    SIP_SKIP static geos::unique_ptr buffer( const GEOSGeometry *geometry, double distance, int segments, Qgis::EndCapStyle endCapStyle, Qgis::JoinStyle joinStyle, double miterLimit, QString *errorMsg = nullptr );
+
     QgsAbstractGeometry *simplify( double tolerance, QString *errorMsg = nullptr ) const override;
     QgsAbstractGeometry *interpolate( double distance, QString *errorMsg = nullptr ) const override;
     QgsAbstractGeometry *envelope( QString *errorMsg = nullptr ) const override;
@@ -380,6 +389,14 @@ class CORE_EXPORT QgsGeos: public QgsGeometryEngine
                                          QgsPointSequence &topologyTestPoints,
                                          QString *errorMsg = nullptr, bool skipIntersectionCheck = false ) const override;
 
+    /**
+     * Directly calculates the offset curve for a GEOS geometry object and returns a GEOS geometry result.
+     *
+     * \note Not available in Python bindings
+     * \since QGIS 3.42
+     */
+    SIP_SKIP static geos::unique_ptr offsetCurve( const GEOSGeometry *geometry, double distance, int segments, Qgis::JoinStyle joinStyle, double miterLimit, QString *errorMsg = nullptr );
+
     QgsAbstractGeometry *offsetCurve( double distance, int segments, Qgis::JoinStyle joinStyle, double miterLimit, QString *errorMsg = nullptr ) const override;
 
     /**

src/core/painting/qgsgeometrypaintdevice.cpp

@@ -20,6 +20,7 @@
 #include "qgsmultipolygon.h"
 #include "qgsmultilinestring.h"
 #include "qgspainting.h"
+#include "qgssymbollayerutils.h"
 
 //
 // QgsGeometryPaintEngine
@@ -395,42 +396,6 @@ void QgsGeometryPaintEngine::addStrokedLine( const QgsLineString *line, double p
   }
 }
 
-Qgis::EndCapStyle QgsGeometryPaintEngine::penStyleToCapStyle( Qt::PenCapStyle style )
-{
-  switch ( style )
-  {
-    case Qt::FlatCap:
-      return Qgis::EndCapStyle::Flat;
-    case Qt::SquareCap:
-      return Qgis::EndCapStyle::Square;
-    case Qt::RoundCap:
-      return Qgis::EndCapStyle::Round;
-    case Qt::MPenCapStyle:
-      // undocumented?
-      break;
-  }
-
-  return Qgis::EndCapStyle::Round;
-}
-
-Qgis::JoinStyle QgsGeometryPaintEngine::penStyleToJoinStyle( Qt::PenJoinStyle style )
-{
-  switch ( style )
-  {
-    case Qt::MiterJoin:
-    case Qt::SvgMiterJoin:
-      return Qgis::JoinStyle::Miter;
-    case Qt::BevelJoin:
-      return Qgis::JoinStyle::Bevel;
-    case Qt::RoundJoin:
-      return Qgis::JoinStyle::Round;
-    case Qt::MPenJoinStyle:
-      // undocumented?
-      break;
-  }
-  return Qgis::JoinStyle::Round;
-}
-
 // based on QPainterPath::toSubpathPolygons()
 void QgsGeometryPaintEngine::addSubpathGeometries( const QPainterPath &path, const QTransform &matrix )
 {
@@ -439,8 +404,8 @@ void QgsGeometryPaintEngine::addSubpathGeometries( const QPainterPath &path, con
 
   const bool transformIsIdentity = matrix.isIdentity();
 
-  const Qgis::EndCapStyle endCapStyle = penStyleToCapStyle( mPen.capStyle() );
-  const Qgis::JoinStyle joinStyle = penStyleToJoinStyle( mPen.joinStyle() );
+  const Qgis::EndCapStyle endCapStyle = QgsSymbolLayerUtils::penCapStyleToEndCapStyle( mPen.capStyle() );
+  const Qgis::JoinStyle joinStyle = QgsSymbolLayerUtils::penJoinStyleToJoinStyle( mPen.joinStyle() );
   const double penWidth = mPen.widthF() <= 0 ? 1 : mPen.widthF();
   const double miterLimit = mPen.miterLimit();
 

src/core/painting/qgsgeometrypaintdevice.h

@@ -103,8 +103,6 @@ class QgsGeometryPaintEngine: public QPaintEngine
 
     void addSubpathGeometries( const QPainterPath &path, const QTransform &matrix );
     void addStrokedLine( const QgsLineString *line, double penWidth, Qgis::EndCapStyle endCapStyle, Qgis::JoinStyle joinStyle, double miterLimit, const QTransform *matrix );
-    static Qgis::EndCapStyle penStyleToCapStyle( Qt::PenCapStyle style );
-    static Qgis::JoinStyle penStyleToJoinStyle( Qt::PenJoinStyle style );
 
     bool mUsePathStroker = false;
     QPen mPen;

src/core/symbology/qgslinesymbollayer.cpp

@@ -32,7 +32,8 @@
 #include "qgscolorrampimpl.h"
 #include "qgsfillsymbol.h"
 #include "qgscolorutils.h"
-
+#include "qgsgeos.h"
+#include "qgspolygon.h"
 #include <algorithm>
 #include <QPainter>
 #include <QDomDocument>
@@ -3952,44 +3953,67 @@ void QgsFilledLineSymbolLayer::renderPolyline( const QPolygonF &points, QgsSymbo
 
   const bool useSelectedColor = shouldRenderUsingSelectionColor( context );
 
-  // stroke out the path using the correct line cap/join style. We'll then use this as the fill polygon
-  QPainterPathStroker stroker;
-  stroker.setWidth( scaledWidth );
-  stroker.setCapStyle( cap );
-  stroker.setJoinStyle( join );
-
-  QPolygonF polygon;
-  if ( qgsDoubleNear( offset, 0 ) )
+  if ( points.count() >= 2 )
   {
-    QPainterPath path;
-    path.addPolygon( points );
-    const QPainterPath stroke = stroker.createStroke( path ).simplified();
-    const QPolygonF polygon = stroke.toFillPolygon();
-    if ( !polygon.isEmpty() )
+    std::unique_ptr< QgsAbstractGeometry > ls = QgsLineString::fromQPolygonF( points );
+    geos::unique_ptr lineGeom;
+
+    if ( !qgsDoubleNear( offset, 0 ) )
     {
-      mFill->renderPolygon( polygon, /* rings */ nullptr, context.feature(), context.renderContext(), -1, useSelectedColor );
+      double scaledOffset = context.renderContext().convertToPainterUnits( offset, mOffsetUnit, mOffsetMapUnitScale );
+      if ( mOffsetUnit == Qgis::RenderUnit::MetersInMapUnits && context.renderContext().flags() & Qgis::RenderContextFlag::RenderSymbolPreview )
+      {
+        // rendering for symbol previews -- a size in meters in map units can't be calculated, so treat the size as millimeters
+        // and clamp it to a reasonable range. It's the best we can do in this situation!
+        scaledOffset = std::min( std::max( context.renderContext().convertToPainterUnits( offset, Qgis::RenderUnit::Millimeters ), 3.0 ), 100.0 );
+      }
+
+      const Qgis::GeometryType geometryType = context.originalGeometryType() != Qgis::GeometryType::Unknown ? context.originalGeometryType() : Qgis::GeometryType::Line;
+      if ( geometryType == Qgis::GeometryType::Polygon )
+      {
+        auto inputPoly = std::make_unique< QgsPolygon >( static_cast< QgsLineString * >( ls.release() ) );
+        geos::unique_ptr g( QgsGeos::asGeos( inputPoly.get() ) );
+        lineGeom = QgsGeos::buffer( g.get(), -scaledOffset, 0, Qgis::EndCapStyle::Flat, Qgis::JoinStyle::Miter, 2 );
+        // the result is a polygon => extract line work
+        QgsGeometry polygon( QgsGeos::fromGeos( lineGeom.get() ) );
+        QVector<QgsGeometry> parts = polygon.coerceToType( Qgis::WkbType::MultiLineString );
+        if ( !parts.empty() )
+        {
+          lineGeom = QgsGeos::asGeos( parts.at( 0 ).constGet() );
+        }
+        else
+        {
+          lineGeom.reset();
+        }
+      }
+      else
+      {
+        geos::unique_ptr g( QgsGeos::asGeos( ls.get() ) );
+        lineGeom = QgsGeos::offsetCurve( g.get(), scaledOffset, 0, Qgis::JoinStyle::Miter, 8.0 );
+      }
     }
-  }
-  else
-  {
-    double scaledOffset = context.renderContext().convertToPainterUnits( offset, mOffsetUnit, mOffsetMapUnitScale );
-    if ( mOffsetUnit == Qgis::RenderUnit::MetersInMapUnits && context.renderContext().flags() & Qgis::RenderContextFlag::RenderSymbolPreview )
+    else
     {
-      // rendering for symbol previews -- a size in meters in map units can't be calculated, so treat the size as millimeters
-      // and clamp it to a reasonable range. It's the best we can do in this situation!
-      scaledOffset = std::min( std::max( context.renderContext().convertToPainterUnits( offset, Qgis::RenderUnit::Millimeters ), 3.0 ), 100.0 );
+      lineGeom = QgsGeos::asGeos( ls.get() );
     }
 
-    const QList<QPolygonF> mline = ::offsetLine( points, scaledOffset, context.originalGeometryType() != Qgis::GeometryType::Unknown ? context.originalGeometryType() : Qgis::GeometryType::Line );
-    for ( const QPolygonF &part : mline )
+    if ( lineGeom )
     {
-      QPainterPath path;
-      path.addPolygon( part );
-      const QPainterPath stroke = stroker.createStroke( path ).simplified();
-      const QPolygonF polygon = stroke.toFillPolygon();
-      if ( !polygon.isEmpty() )
+      geos::unique_ptr buffered = QgsGeos::buffer( lineGeom.get(), scaledWidth / 2, 8,
+                                  QgsSymbolLayerUtils::penCapStyleToEndCapStyle( cap ),
+                                  QgsSymbolLayerUtils::penJoinStyleToJoinStyle( join ), 8 );
+      if ( buffered )
       {
-        mFill->renderPolygon( polygon, /* rings */ nullptr, context.feature(), context.renderContext(), -1, useSelectedColor );
+        // convert to rings
+        std::unique_ptr< QgsAbstractGeometry > bufferedGeom = QgsGeos::fromGeos( buffered.get() );
+        const QList< QList< QPolygonF > > parts = QgsSymbolLayerUtils::toQPolygonF( bufferedGeom.get(), Qgis::SymbolType::Fill );
+        for ( const QList< QPolygonF > &polygon : parts )
+        {
+          QVector< QPolygonF > rings;
+          for ( int i = 1; i < polygon.size(); ++i )
+            rings << polygon.at( i );
+          mFill->renderPolygon( polygon.value( 0 ), &rings, context.feature(), context.renderContext(), -1, useSelectedColor );
+        }
       }
     }
   }