Allow for exact calculation of symbol sizes with mixed layer units

Fixes #21143

(cherry picked from commit 867e399)

Author: nyalldawson

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

@@ -223,6 +223,8 @@ Create a new MarkerLineSymbolLayerV2 from SLD
 
     virtual double width() const;
 
+    virtual double width( const QgsRenderContext &context ) const;
+
 
     virtual double estimateMaxBleed( const QgsRenderContext &context ) const;
 

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

@@ -687,6 +687,10 @@ Will take ownership.
 
 class QgsMarkerSymbol : QgsSymbol
 {
+%Docstring
+
+A marker symbol type, for rendering Point and MultiPoint geometries.
+%End
 
 %TypeHeaderCode
 #include "qgssymbol.h"
@@ -700,6 +704,11 @@ This is a convenience method for easier creation of marker symbols.
 %End
 
     QgsMarkerSymbol( const QgsSymbolLayerList &layers /Transfer/ = QgsSymbolLayerList() );
+%Docstring
+Constructor for QgsMarkerSymbol, with the specified list of initial symbol ``layers``.
+
+Ownership of the ``layers`` are transferred to the symbol.
+%End
 
     void setAngle( double symbolAngle );
 %Docstring
@@ -770,14 +779,37 @@ will be scaled to maintain their current relative size to the whole symbol size.
 
     double size() const;
 %Docstring
-Returns the size for the whole symbol, which is the maximum size of
+Returns the estimated size for the whole symbol, which is the maximum size of
 all marker symbol layers in the symbol.
 
+.. warning::
+
+   This returned value is inaccurate if the symbol consists of multiple
+   symbol layers with different size units. Use the overload accepting a :py:class:`QgsRenderContext`
+   argument instead for accurate sizes in this case.
+
 .. seealso:: :py:func:`setSize`
 
 .. seealso:: :py:func:`sizeUnit`
 
 .. seealso:: :py:func:`sizeMapUnitScale`
+%End
+
+    double size( const QgsRenderContext &context ) const;
+%Docstring
+Returns the symbol size, in painter units. This is the maximum size of
+all marker symbol layers in the symbol.
+
+This method returns an accurate size by calculating the actual rendered
+size of each symbol layer using the provided render ``context``.
+
+.. seealso:: :py:func:`setSize`
+
+.. seealso:: :py:func:`sizeUnit`
+
+.. seealso:: :py:func:`sizeMapUnitScale`
+
+.. versionadded:: 3.4.5
 %End
 
     void setSizeUnit( QgsUnitTypes::RenderUnit unit );
@@ -890,6 +922,10 @@ and stopRender() calls, or data defined rotation and offset will not be correctl
 
 class QgsLineSymbol : QgsSymbol
 {
+%Docstring
+
+A line symbol type, for rendering LineString and MultiLineString geometries.
+%End
 
 %TypeHeaderCode
 #include "qgssymbol.h"
@@ -903,9 +939,46 @@ This is a convenience method for easier creation of line symbols.
 %End
 
     QgsLineSymbol( const QgsSymbolLayerList &layers /Transfer/ = QgsSymbolLayerList() );
+%Docstring
+Constructor for QgsLineSymbol, with the specified list of initial symbol ``layers``.
+
+Ownership of the ``layers`` are transferred to the symbol.
+%End
 
     void setWidth( double width );
+%Docstring
+Sets the ``width`` for the whole line symbol. Individual symbol layer sizes
+will be scaled to maintain their current relative size to the whole symbol size.
+
+.. seealso:: :py:func:`width`
+%End
+
     double width() const;
+%Docstring
+Returns the estimated width for the whole symbol, which is the maximum width of
+all marker symbol layers in the symbol.
+
+.. warning::
+
+   This returned value is inaccurate if the symbol consists of multiple
+   symbol layers with different width units. Use the overload accepting a :py:class:`QgsRenderContext`
+   argument instead for accurate sizes in this case.
+
+.. seealso:: :py:func:`setWidth`
+%End
+
+    double width( const QgsRenderContext &context ) const;
+%Docstring
+Returns the symbol width, in painter units. This is the maximum width of
+all marker symbol layers in the symbol.
+
+This method returns an accurate width by calculating the actual rendered
+width of each symbol layer using the provided render ``context``.
+
+.. seealso:: :py:func:`setWidth`
+
+.. versionadded:: 3.4.5
+%End
 
     void setDataDefinedWidth( const QgsProperty &property );
 %Docstring
@@ -938,6 +1011,10 @@ Returns data defined width for whole symbol (including all symbol layers).
 
 class QgsFillSymbol : QgsSymbol
 {
+%Docstring
+
+A fill symbol type, for rendering Polygon and MultiPolygon geometries.
+%End
 
 %TypeHeaderCode
 #include "qgssymbol.h"
@@ -951,6 +1028,11 @@ This is a convenience method for easier creation of fill symbols.
 %End
 
     QgsFillSymbol( const QgsSymbolLayerList &layers /Transfer/ = QgsSymbolLayerList() );
+%Docstring
+Constructor for QgsFillSymbol, with the specified list of initial symbol ``layers``.
+
+Ownership of the ``layers`` are transferred to the symbol.
+%End
     void setAngle( double angle );
     void renderPolygon( const QPolygonF &points, QList<QPolygonF> *rings, const QgsFeature *f, QgsRenderContext &context, int layer = -1, bool selected = false );
 

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

@@ -835,7 +835,31 @@ class QgsLineSymbolLayer : QgsSymbolLayer
     virtual void renderPolygonStroke( const QPolygonF &points, QList<QPolygonF> *rings, QgsSymbolRenderContext &context );
 
     virtual void setWidth( double width );
+
     virtual double width() const;
+%Docstring
+Returns the estimated width for the line symbol layer.
+
+.. warning::
+
+   This returned value is inaccurate if the symbol layer has sub-symbols with
+   different width units. Use the overload accepting a :py:class:`QgsRenderContext`
+   argument instead for accurate sizes in this case.
+
+.. seealso:: :py:func:`setWidth`
+%End
+
+    virtual double width( const QgsRenderContext &context ) const;
+%Docstring
+Returns the line symbol layer width, in painter units.
+
+This method returns an accurate width by calculating the actual rendered
+width of the symbol layer using the provided render ``context``.
+
+.. seealso:: :py:func:`setWidth`
+
+.. versionadded:: 3.4.5
+%End
 
     double offset() const;
     void setOffset( double offset );

src/core/layertree/qgslayertreemodellegendnode.cpp

@@ -390,7 +390,7 @@ QSizeF QgsSymbolLegendNode::drawSymbol( const QgsLegendSettings &settings, ItemC
   if ( QgsMarkerSymbol *markerSymbol = dynamic_cast<QgsMarkerSymbol *>( s ) )
   {
     // allow marker symbol to occupy bigger area if necessary
-    double size = context.convertToPainterUnits( markerSymbol->size(), markerSymbol->sizeUnit(), markerSymbol->sizeMapUnitScale() ) / context.scaleFactor();
+    double size = markerSymbol->size( context ) / context.scaleFactor();
     height = size;
     width = size;
     if ( width < settings.symbolSize().width() )

src/core/symbology/qgslinesymbollayer.cpp

@@ -1113,7 +1113,8 @@ void QgsMarkerLineSymbolLayer::renderPolylineVertex( const QPolygonF &points, Qg
            || ( placement == CurvePoint && vId.type == QgsVertexId::CurveVertex ) )
       {
         //transform
-        x = vPoint.x(), y = vPoint.y();
+        x = vPoint.x();
+        y = vPoint.y();
         z = 0.0;
         if ( ct.isValid() )
         {
@@ -1618,6 +1619,11 @@ double QgsMarkerLineSymbolLayer::width() const
   return mMarker->size();
 }
 
+double QgsMarkerLineSymbolLayer::width( const QgsRenderContext &context ) const
+{
+  return mMarker->size( context );
+}
+
 void QgsMarkerLineSymbolLayer::setOutputUnit( QgsUnitTypes::RenderUnit unit )
 {
   QgsLineSymbolLayer::setOutputUnit( unit );
@@ -1675,7 +1681,7 @@ bool QgsMarkerLineSymbolLayer::hasDataDefinedProperties() const
 
 double QgsMarkerLineSymbolLayer::estimateMaxBleed( const QgsRenderContext &context ) const
 {
-  return context.convertToPainterUnits( ( mMarker->size() / 2.0 ), mMarker->sizeUnit(), mMarker->sizeMapUnitScale() ) +
+  return ( mMarker->size( context ) / 2.0 ) +
          context.convertToPainterUnits( std::fabs( mOffset ), mOffsetUnit, mOffsetMapUnitScale );
 }
 

src/core/symbology/qgslinesymbollayer.h

@@ -234,6 +234,7 @@ class CORE_EXPORT QgsMarkerLineSymbolLayer : public QgsLineSymbolLayer
 
     void setWidth( double width ) override;
     double width() const override;
+    double width( const QgsRenderContext &context ) const override;
 
     double estimateMaxBleed( const QgsRenderContext &context ) const override;
 

src/core/symbology/qgspointdisplacementrenderer.cpp

@@ -61,12 +61,11 @@ void QgsPointDisplacementRenderer::drawGroup( QPointF centerPoint, QgsRenderCont
   //calculate max diagonal size from all symbols in group
   double diagonal = 0;
 
-  Q_FOREACH ( const GroupedFeature &feature, group )
+  for ( const GroupedFeature &feature : group )
   {
     if ( QgsMarkerSymbol *symbol = feature.symbol() )
     {
-      diagonal = std::max( diagonal, context.convertToPainterUnits( M_SQRT2 * symbol->size(),
-                           symbol->sizeUnit(), symbol->sizeMapUnitScale() ) );
+      diagonal = std::max( diagonal, M_SQRT2 * symbol->size( context ) );
     }
   }
 
@@ -274,8 +273,7 @@ void QgsPointDisplacementRenderer::calculateSymbolAndLabelPositions( QgsSymbolRe
     }
     case ConcentricRings:
     {
-      double centerDiagonal = symbolContext.renderContext().convertToPainterUnits( M_SQRT2 * mCenterSymbol->size(),
-                              mCenterSymbol->sizeUnit(), mCenterSymbol->sizeMapUnitScale() );
+      double centerDiagonal = mCenterSymbol->size( symbolContext.renderContext() ) * M_SQRT2;
 
       int pointsRemaining = nPosition;
       int ringNumber = 1;
@@ -307,8 +305,7 @@ void QgsPointDisplacementRenderer::calculateSymbolAndLabelPositions( QgsSymbolRe
     }
     case Grid:
     {
-      double centerDiagonal = symbolContext.renderContext().convertToPainterUnits( M_SQRT2 * mCenterSymbol->size(),
-                              mCenterSymbol->sizeUnit(), mCenterSymbol->sizeMapUnitScale() );
+      double centerDiagonal = mCenterSymbol->size( symbolContext.renderContext() ) * M_SQRT2;
       int pointsRemaining = nPosition;
       gridSize = std::ceil( std::sqrt( pointsRemaining ) );
       if ( pointsRemaining - std::pow( gridSize - 1, 2 ) < gridSize )

src/core/symbology/qgssymbol.cpp

@@ -1303,6 +1303,21 @@ double QgsMarkerSymbol::size() const
   return maxSize;
 }
 
+double QgsMarkerSymbol::size( const QgsRenderContext &context ) const
+{
+  // return size of the largest symbol
+  double maxSize = 0;
+  for ( QgsSymbolLayer *layer : mLayers )
+  {
+    if ( layer->type() != QgsSymbol::Marker )
+      continue;
+    const QgsMarkerSymbolLayer *markerLayer = static_cast<const QgsMarkerSymbolLayer *>( layer );
+    const double layerSize = context.convertToPainterUnits( markerLayer->size(), markerLayer->sizeUnit(), markerLayer->sizeMapUnitScale() );
+    maxSize = std::max( maxSize, layerSize );
+  }
+  return maxSize;
+}
+
 void QgsMarkerSymbol::setSizeUnit( QgsUnitTypes::RenderUnit unit )
 {
   Q_FOREACH ( QgsSymbolLayer *layer, mLayers )
@@ -1625,6 +1640,21 @@ double QgsLineSymbol::width() const
   return maxWidth;
 }
 
+double QgsLineSymbol::width( const QgsRenderContext &context ) const
+{
+  // return width of the largest symbol
+  double maxWidth = 0;
+  for ( QgsSymbolLayer *layer : mLayers )
+  {
+    if ( layer->type() != QgsSymbol::Line )
+      continue;
+    const QgsLineSymbolLayer *lineLayer = static_cast<const QgsLineSymbolLayer *>( layer );
+    const double layerWidth = lineLayer->width( context );
+    maxWidth = std::max( maxWidth, layerWidth );
+  }
+  return maxWidth;
+}
+
 void QgsLineSymbol::setDataDefinedWidth( const QgsProperty &property )
 {
   const double symbolWidth = width();