[legends] Fix corrupted data defined legend rendering in layout designer

Fixes qgis#36765
Fixes qgis#34658

python/core/auto_generated/qgsdatadefinedsizelegend.sip.in

@@ -74,6 +74,26 @@ Sets marker symbol that will be used to draw markers in legend
     QgsMarkerSymbol *symbol() const;
 %Docstring
 Returns marker symbol that will be used to draw markers in legend
+%End
+
+    void setLineSymbol( QgsLineSymbol *symbol /Transfer/ );
+%Docstring
+Sets the line ``symbol`` that will be used to draw callout lines in legend.
+
+Ownership of ``symbol`` is transferred.
+
+.. seealso:: :py:func:`lineSymbol`
+
+.. versionadded:: 3.14
+%End
+
+    QgsLineSymbol *lineSymbol() const;
+%Docstring
+Returns the line symbol that will be used to draw callout lines in legend.
+
+.. seealso:: :py:func:`setLineSymbol`
+
+.. versionadded:: 3.14
 %End
 
     void setSizeScaleTransformer( QgsSizeScaleTransformer *transformer /Transfer/ );

src/core/layertree/qgslayertreemodellegendnode.cpp

@@ -1219,6 +1219,8 @@ QgsLayerTreeModelLegendNode::ItemMetrics QgsDataDefinedSizeLegendNode::draw( con
   {
     context->painter()->save();
     context->painter()->translate( ctx->columnLeft, ctx->top );
+
+    // scale to pixels
     context->painter()->scale( 1 / context->scaleFactor(), 1 / context->scaleFactor() );
   }
 

src/core/qgsdatadefinedsizelegend.cpp

@@ -19,9 +19,15 @@
 #include "qgspropertytransformer.h"
 #include "qgssymbollayerutils.h"
 #include "qgsxmlutils.h"
+#include "qgslinesymbollayer.h"
+#include "qgstextformat.h"
+#include "qgstextrenderer.h"
 
-
-QgsDataDefinedSizeLegend::QgsDataDefinedSizeLegend() = default;
+QgsDataDefinedSizeLegend::QgsDataDefinedSizeLegend()
+{
+  std::unique_ptr< QgsSimpleLineSymbolLayer > lineSymbolLayer = qgis::make_unique< QgsSimpleLineSymbolLayer >( QColor( 0, 0, 0 ), 0.2 );
+  mLineSymbol = qgis::make_unique< QgsLineSymbol >( QgsSymbolLayerList() << lineSymbolLayer.release() );
+}
 
 QgsDataDefinedSizeLegend::~QgsDataDefinedSizeLegend() = default;
 
@@ -30,6 +36,7 @@ QgsDataDefinedSizeLegend::QgsDataDefinedSizeLegend( const QgsDataDefinedSizeLege
   , mTitleLabel( other.mTitleLabel )
   , mSizeClasses( other.mSizeClasses )
   , mSymbol( other.mSymbol.get() ? other.mSymbol->clone() : nullptr )
+  , mLineSymbol( other.mLineSymbol.get() ? other.mLineSymbol->clone() : nullptr )
   , mSizeScaleTransformer( other.mSizeScaleTransformer.get() ? new QgsSizeScaleTransformer( *other.mSizeScaleTransformer ) : nullptr )
   , mVAlign( other.mVAlign )
   , mFont( other.mFont )
@@ -46,6 +53,7 @@ QgsDataDefinedSizeLegend &QgsDataDefinedSizeLegend::operator=( const QgsDataDefi
     mTitleLabel = other.mTitleLabel;
     mSizeClasses = other.mSizeClasses;
     mSymbol.reset( other.mSymbol.get() ? other.mSymbol->clone() : nullptr );
+    mLineSymbol.reset( other.mLineSymbol.get() ? other.mLineSymbol->clone() : nullptr );
     mSizeScaleTransformer.reset( other.mSizeScaleTransformer.get() ? new QgsSizeScaleTransformer( *other.mSizeScaleTransformer ) : nullptr );
     mVAlign = other.mVAlign;
     mFont = other.mFont;
@@ -65,6 +73,16 @@ QgsMarkerSymbol *QgsDataDefinedSizeLegend::symbol() const
   return mSymbol.get();
 }
 
+void QgsDataDefinedSizeLegend::setLineSymbol( QgsLineSymbol *symbol )
+{
+  mLineSymbol.reset( symbol );
+}
+
+QgsLineSymbol *QgsDataDefinedSizeLegend::lineSymbol() const
+{
+  return mLineSymbol.get();
+}
+
 void QgsDataDefinedSizeLegend::setSizeScaleTransformer( QgsSizeScaleTransformer *transformer )
 {
   mSizeScaleTransformer.reset( transformer );
@@ -143,6 +161,8 @@ QgsLegendSymbolList QgsDataDefinedSizeLegend::legendSymbolList() const
 
 void QgsDataDefinedSizeLegend::drawCollapsedLegend( QgsRenderContext &context, QSizeF *outputSize, double *labelXOffset ) const
 {
+  // this assumes the context's painter has been scaled to pixels in advance!
+
   if ( mType != LegendCollapsed || mSizeClasses.isEmpty() || !mSymbol )
   {
     if ( outputSize )
@@ -273,26 +293,42 @@ void QgsDataDefinedSizeLegend::drawCollapsedLegend( QgsRenderContext &context, Q
         p->translate( tx, outputLargestSize - outputSymbolSize );
         break;
     }
-    s->drawPreviewIcon( p, QSize( outputSymbolSize, outputSymbolSize ) );
+    s->drawPreviewIcon( nullptr, QSize( outputSymbolSize, outputSymbolSize ), &context );
     p->restore();
   }
 
-  p->setPen( mTextColor );
-  p->setFont( mFont );
+  QgsTextFormat format = QgsTextFormat::fromQFont( mFont );
+  format.setColor( mTextColor );
+
+  if ( mLineSymbol )
+  {
+    mLineSymbol->setColor( mTextColor );
+    mLineSymbol->startRender( context );
+  }
 
   int i = 0;
   for ( const SizeClass &c : qgis::as_const( classes ) )
   {
     // line from symbol to the text
-    p->drawLine( outputLargestSize / 2, symbolTopY[i], outputLargestSize + hLengthLine, textCenterY[i] );
+    if ( mLineSymbol )
+    {
+      mLineSymbol->renderPolyline( QPolygonF() << QPointF( outputLargestSize / 2, symbolTopY[i] )
+                                   << QPointF( outputLargestSize + hLengthLine, textCenterY[i] ), nullptr, context );
+    }
 
     // draw label
     QRect rect( outputLargestSize + hLengthLine + hSpaceLineText, textCenterY[i] - textHeight / 2,
                 maxTextWidth, textHeight );
-    p->drawText( rect, mTextAlignment, c.label );
+
+    QgsTextRenderer::drawText( rect, 0, mTextAlignment == Qt::AlignRight ? QgsTextRenderer::AlignRight :
+                               mTextAlignment == Qt::AlignHCenter ? QgsTextRenderer::AlignCenter : QgsTextRenderer::AlignLeft,
+                               QStringList() << c.label, context, format );
     i++;
   }
 
+  if ( mLineSymbol )
+    mLineSymbol->stopRender( context );
+
   p->restore();
 }
 
@@ -344,6 +380,12 @@ QgsDataDefinedSizeLegend *QgsDataDefinedSizeLegend::readXml( const QDomElement &
     ddsLegend->setSymbol( QgsSymbolLayerUtils::loadSymbol<QgsMarkerSymbol>( elemSymbol, context ) );
   }
 
+  QDomElement lineSymbol = elem.firstChildElement( QStringLiteral( "lineSymbol" ) );
+  if ( !lineSymbol.isNull() )
+  {
+    ddsLegend->setLineSymbol( QgsSymbolLayerUtils::loadSymbol<QgsLineSymbol>( lineSymbol, context ) );
+  }
+
   QgsSizeScaleTransformer *transformer = nullptr;
   QDomElement elemTransformer = elem.firstChildElement( QStringLiteral( "transformer" ) );
   if ( !elemTransformer.isNull() )
@@ -396,6 +438,12 @@ void QgsDataDefinedSizeLegend::writeXml( QDomElement &elem, const QgsReadWriteCo
     elem.appendChild( elemSymbol );
   }
 
+  if ( mLineSymbol )
+  {
+    QDomElement elemSymbol = QgsSymbolLayerUtils::saveSymbol( QStringLiteral( "lineSymbol" ), mLineSymbol.get(), doc, context );
+    elem.appendChild( elemSymbol );
+  }
+
   if ( mSizeScaleTransformer )
   {
     QDomElement elemTransformer = QgsXmlUtils::writeVariant( mSizeScaleTransformer->toVariant(), doc );

src/core/qgsdatadefinedsizelegend.h

@@ -27,6 +27,7 @@ class QgsProperty;
 class QgsReadWriteContext;
 class QgsRenderContext;
 class QgsSizeScaleTransformer;
+class QgsLineSymbol;
 
 
 /**
@@ -85,6 +86,23 @@ class CORE_EXPORT QgsDataDefinedSizeLegend
     //! Returns marker symbol that will be used to draw markers in legend
     QgsMarkerSymbol *symbol() const;
 
+    /**
+     * Sets the line \a symbol that will be used to draw callout lines in legend.
+     *
+     * Ownership of \a symbol is transferred.
+     *
+     * \see lineSymbol()
+     * \since QGIS 3.14
+     */
+    void setLineSymbol( QgsLineSymbol *symbol SIP_TRANSFER );
+
+    /**
+    * Returns the line symbol that will be used to draw callout lines in legend.
+    * \see setLineSymbol()
+    * \since QGIS 3.14
+    */
+    QgsLineSymbol *lineSymbol() const;
+
     //! Sets transformer for scaling of symbol sizes. Takes ownership of the object. Accepts NULLPTR to set no transformer.
     void setSizeScaleTransformer( QgsSizeScaleTransformer *transformer SIP_TRANSFER );
     //! Returns transformer for scaling of symbol sizes. Returns NULLPTR if no transformer is defined.
@@ -149,6 +167,7 @@ class CORE_EXPORT QgsDataDefinedSizeLegend
     QString mTitleLabel;  //!< Title label for the following size-based item(s)
     QList< SizeClass > mSizeClasses;  //!< List of classes: symbol size (in whatever units symbol uses) + label
     std::unique_ptr<QgsMarkerSymbol> mSymbol;
+    std::unique_ptr<QgsLineSymbol> mLineSymbol;
     std::unique_ptr<QgsSizeScaleTransformer> mSizeScaleTransformer;  //!< Optional transformer for classes
     VerticalAlignment mVAlign = AlignBottom;
     QFont mFont;