Add proper method to determine whether a symbol uses map unit sizes,

and use this to determine whether a legend item needs updating
as a result of a map change

This results in a HUGE speed up when loading large projects where
symbols don't use Millimeter based sizes, as the previous code
assumed only that any non-millimeter size was a map unit based size.

(cherry picked from commit 0ab761c)

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

@@ -45,6 +45,8 @@ Create a new QgsArrowSymbolLayer
 
     virtual bool hasDataDefinedProperties() const;
 
+    virtual bool usesMapUnits() const;
+
 
     double arrowWidth() const;
 %Docstring

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

@@ -152,6 +152,8 @@ Returns the units for the symbol's stroke width.
 
     virtual QgsUnitTypes::RenderUnit outputUnit() const;
 
+    virtual bool usesMapUnits() const;
+
 
     virtual void setMapUnitScale( const QgsMapUnitScale &scale );
 

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

@@ -159,6 +159,8 @@ Returns the map unit scale for the fill's offset.
 
     virtual QgsUnitTypes::RenderUnit outputUnit() const;
 
+    virtual bool usesMapUnits() const;
+
 
     virtual void setMapUnitScale( const QgsMapUnitScale &scale );
 
@@ -400,6 +402,8 @@ Returns the map unit scale for the fill's offset.
 
     virtual QgsUnitTypes::RenderUnit outputUnit() const;
 
+    virtual bool usesMapUnits() const;
+
 
     virtual void setMapUnitScale( const QgsMapUnitScale &scale );
 
@@ -743,6 +747,8 @@ Returns the units used for the offset of the shapeburst fill.
 
     virtual QgsUnitTypes::RenderUnit outputUnit() const;
 
+    virtual bool usesMapUnits() const;
+
 
     virtual void setMapUnitScale( const QgsMapUnitScale &scale );
 
@@ -904,6 +910,8 @@ Used internally when reading/writing symbols.
 
     virtual double estimateMaxBleed( const QgsRenderContext &context ) const;
 
+    virtual bool usesMapUnits() const;
+
 
     virtual QgsSymbol *subSymbol();
     virtual bool setSubSymbol( QgsSymbol *symbol /Transfer/ );
@@ -1185,6 +1193,8 @@ Used internally when reading/writing symbols.
 
     virtual void toSld( QDomDocument &doc, QDomElement &element, const QgsStringMap &props ) const;
 
+    virtual bool usesMapUnits() const;
+
 
     void setSvgFilePath( const QString &svgPath );
 %Docstring
@@ -1658,6 +1668,8 @@ Returns the map unit scale for the pattern's line offset.
 
     virtual QgsUnitTypes::RenderUnit outputUnit() const;
 
+    virtual bool usesMapUnits() const;
+
     virtual void setMapUnitScale( const QgsMapUnitScale &scale );
 
     virtual QgsMapUnitScale mapUnitScale() const;
@@ -1976,6 +1988,8 @@ Returns the unit scale for the vertical offset between rows in the pattern.
 
     virtual QgsUnitTypes::RenderUnit outputUnit() const;
 
+    virtual bool usesMapUnits() const;
+
 
     virtual void setMapUnitScale( const QgsMapUnitScale &scale );
 
@@ -2062,6 +2076,8 @@ Caller takes ownership of the returned symbol layer.
 
     virtual QgsUnitTypes::RenderUnit outputUnit() const;
 
+    virtual bool usesMapUnits() const;
+
 
     virtual void setMapUnitScale( const QgsMapUnitScale &scale );
 
@@ -2254,6 +2270,8 @@ Caller takes ownership of the returned symbol layer.
 
     virtual QgsUnitTypes::RenderUnit outputUnit() const;
 
+    virtual bool usesMapUnits() const;
+
 
     virtual void setMapUnitScale( const QgsMapUnitScale &scale );
 

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

@@ -46,6 +46,8 @@ that is created by this generator.
 
     virtual void stopFeatureRender( const QgsFeature &feature, QgsRenderContext &context );
 
+    virtual bool usesMapUnits() const;
+
 
     virtual QgsSymbolLayer *clone() const /Factory/;
 

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

@@ -66,6 +66,8 @@ Creates a new QgsSimpleLineSymbolLayer from an SLD XML DOM ``element``.
 
     virtual QgsUnitTypes::RenderUnit outputUnit() const;
 
+    virtual bool usesMapUnits() const;
+
     virtual void setMapUnitScale( const QgsMapUnitScale &scale );
 
     virtual QgsMapUnitScale mapUnitScale() const;
@@ -770,6 +772,8 @@ Creates a new QgsMarkerLineSymbolLayer from an SLD XML DOM ``element``.
 
     virtual void setOutputUnit( QgsUnitTypes::RenderUnit unit );
 
+    virtual bool usesMapUnits() const;
+
     virtual QSet<QString> usedAttributes( const QgsRenderContext &context ) const;
 
     virtual bool hasDataDefinedProperties() const;
@@ -880,6 +884,8 @@ serialized in the ``properties`` map (corresponding to the output from
 
     virtual void setDataDefinedProperty( QgsSymbolLayer::Property key, const QgsProperty &property );
 
+    virtual bool usesMapUnits() const;
+
 
     double hashAngle() const;
 %Docstring

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

@@ -260,6 +260,8 @@ Creates a new QgsSimpleMarkerSymbolLayer from an SLD XML element.
 
     virtual QgsMapUnitScale mapUnitScale() const;
 
+    virtual bool usesMapUnits() const;
+
     virtual QRectF bounds( QPointF point, QgsSymbolRenderContext &context );
 
     virtual QColor fillColor() const;
@@ -512,6 +514,8 @@ Creates a new QgsFilledMarkerSymbolLayer.
 
     virtual QColor color() const;
 
+    virtual bool usesMapUnits() const;
+
 
   private:
     QgsFilledMarkerSymbolLayer( const QgsFilledMarkerSymbolLayer & );
@@ -563,6 +567,8 @@ Used internally when reading/writing symbols.
 
     virtual QgsStringMap properties() const;
 
+    virtual bool usesMapUnits() const;
+
 
     virtual QgsSvgMarkerSymbolLayer *clone() const /Factory/;
 
@@ -749,6 +755,8 @@ Used internally when reading/writing symbols.
 
     virtual QgsRasterMarkerSymbolLayer *clone() const /Factory/;
 
+    virtual bool usesMapUnits() const;
+
 
     double calculateAspectRatio( QgsSymbolRenderContext &context, double scaledSize, bool &hasDataDefinedAspectRatio ) const;
 %Docstring
@@ -911,6 +919,8 @@ Creates a new QgsFontMarkerSymbolLayer from an SLD XML ``element``.
 
     virtual void writeSldMarker( QDomDocument &doc, QDomElement &element, const QgsStringMap &props ) const;
 
+    virtual bool usesMapUnits() const;
+
 
 
     QString fontFamily() const;

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

@@ -59,6 +59,8 @@ Create a new QgsMaskMarkerSymbolLayer
 
     virtual QRectF bounds( QPointF point, QgsSymbolRenderContext &context );
 
+    virtual bool usesMapUnits() const;
+
 
     virtual void drawPreviewIcon( QgsSymbolRenderContext &context, QSize size );
 

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

@@ -369,6 +369,13 @@ may use it to specify the units for the line width.
 :return: output unit, or QgsUnitTypes.RenderUnknownUnit if the symbol contains mixed units
 
 .. seealso:: :py:func:`setOutputUnit`
+%End
+
+    bool usesMapUnits() const;
+%Docstring
+Returns ``True`` if the symbol has any components which use map unit based sizes.
+
+.. versionadded:: 3.18
 %End
 
     void setOutputUnit( QgsUnitTypes::RenderUnit unit );

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

@@ -369,6 +369,13 @@ layer may use it to specify the units for the line width.
 :return: output unit, or QgsUnitTypes.RenderUnknownUnit if the symbol layer contains mixed units
 
 .. seealso:: :py:func:`setOutputUnit`
+%End
+
+    virtual bool usesMapUnits() const;
+%Docstring
+Returns ``True`` if the symbol layer has any components which use map unit based sizes.
+
+.. versionadded:: 3.18
 %End
 
     virtual void setMapUnitScale( const QgsMapUnitScale &scale );

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

@@ -65,6 +65,8 @@ A symbol layer class for displaying displacement arrows based on point layer att
 
     virtual QgsStringMap properties() const;
 
+    virtual bool usesMapUnits() const;
+
 
     virtual void toSld( QDomDocument &doc, QDomElement &element, const QgsStringMap &props ) const;
 

src/core/layertree/qgslayertreemodellegendnode.cpp

@@ -266,8 +266,10 @@ QgsSymbolLegendNode::QgsSymbolLegendNode( QgsLayerTreeLayer *nodeLayer, const Qg
   connect( qobject_cast<QgsVectorLayer *>( nodeLayer->layer() ), &QgsVectorLayer::symbolFeatureCountMapChanged, this, &QgsSymbolLegendNode::updateLabel );
   connect( nodeLayer, &QObject::destroyed, this, [ = ]() { mLayerNode = nullptr; } );
 
-  if ( auto *lSymbol = mItem.symbol() )
-    mSymbolUsesMapUnits = ( lSymbol->outputUnit() != QgsUnitTypes::RenderMillimeters );
+  if ( const QgsSymbol *symbol = mItem.symbol() )
+  {
+    mSymbolUsesMapUnits = symbol->usesMapUnits();
+  }
 }
 
 Qt::ItemFlags QgsSymbolLegendNode::flags() const

src/core/symbology/qgsarrowsymbollayer.cpp

@@ -174,6 +174,16 @@ bool QgsArrowSymbolLayer::hasDataDefinedProperties() const
   return false;
 }
 
+bool QgsArrowSymbolLayer::usesMapUnits() const
+{
+  return mArrowWidthUnit == QgsUnitTypes::RenderMapUnits || mArrowWidthUnit == QgsUnitTypes::RenderMetersInMapUnits
+         || mArrowStartWidthUnit == QgsUnitTypes::RenderMapUnits || mArrowStartWidthUnit == QgsUnitTypes::RenderMetersInMapUnits
+         || mHeadLengthUnit == QgsUnitTypes::RenderMapUnits || mHeadLengthUnit == QgsUnitTypes::RenderMetersInMapUnits
+         || mHeadThicknessUnit == QgsUnitTypes::RenderMapUnits || mHeadThicknessUnit == QgsUnitTypes::RenderMetersInMapUnits
+         || mWidthUnit == QgsUnitTypes::RenderMapUnits || mWidthUnit == QgsUnitTypes::RenderMetersInMapUnits
+         || mOffsetUnit == QgsUnitTypes::RenderMapUnits || mOffsetUnit == QgsUnitTypes::RenderMetersInMapUnits;
+}
+
 void QgsArrowSymbolLayer::startRender( QgsSymbolRenderContext &context )
 {
   mExpressionScope.reset( new QgsExpressionContextScope() );

src/core/symbology/qgsarrowsymbollayer.h

@@ -48,6 +48,7 @@ class CORE_EXPORT QgsArrowSymbolLayer : public QgsLineSymbolLayer
     bool setSubSymbol( QgsSymbol *symbol SIP_TRANSFER ) override;
     QSet<QString> usedAttributes( const QgsRenderContext &context ) const override;
     bool hasDataDefinedProperties() const override;
+    bool usesMapUnits() const override;
 
     //! Gets current arrow width
     double arrowWidth() const { return mArrowWidth; }

src/core/symbology/qgsellipsesymbollayer.cpp

@@ -665,6 +665,14 @@ QgsUnitTypes::RenderUnit QgsEllipseSymbolLayer::outputUnit() const
   return unit;
 }
 
+bool QgsEllipseSymbolLayer::usesMapUnits() const
+{
+  return mSymbolWidthUnit == QgsUnitTypes::RenderMapUnits || mSymbolWidthUnit == QgsUnitTypes::RenderMetersInMapUnits
+         || mSymbolHeightUnit == QgsUnitTypes::RenderMapUnits || mSymbolHeightUnit == QgsUnitTypes::RenderMetersInMapUnits
+         || mStrokeWidthUnit == QgsUnitTypes::RenderMapUnits || mStrokeWidthUnit == QgsUnitTypes::RenderMetersInMapUnits
+         || mOffsetUnit == QgsUnitTypes::RenderMapUnits || mOffsetUnit == QgsUnitTypes::RenderMetersInMapUnits;
+}
+
 void QgsEllipseSymbolLayer::setMapUnitScale( const QgsMapUnitScale &scale )
 {
   QgsMarkerSymbolLayer::setMapUnitScale( scale );

src/core/symbology/qgsellipsesymbollayer.h

@@ -137,6 +137,7 @@ class CORE_EXPORT QgsEllipseSymbolLayer: public QgsMarkerSymbolLayer
 
     void setOutputUnit( QgsUnitTypes::RenderUnit unit ) override;
     QgsUnitTypes::RenderUnit outputUnit() const override;
+    bool usesMapUnits() const override;
 
     void setMapUnitScale( const QgsMapUnitScale &scale ) override;
     QgsMapUnitScale mapUnitScale() const override;