QVariantMap QgsProcessingFeatureBasedAlgorithm::processAlgorithm( const QVariantMap &parameters, QgsProcessingContext &context, QgsProcessingFeedback *feedback )
{
  prepareSource( parameters, context );
  QString dest;
  std::unique_ptr< QgsFeatureSink > sink( parameterAsSink( parameters, QStringLiteral( "OUTPUT" ), context, dest,
                                          outputFields( mSource->fields() ),
                                          outputWkbType( mSource->wkbType() ),
                                          outputCrs( mSource->sourceCrs() ),
                                          sinkFlags() ) );
  if ( !sink )
    throw QgsProcessingException( invalidSinkError( parameters, QStringLiteral( "OUTPUT" ) ) );

  // prepare expression context for feature iteration
  QgsExpressionContext prevContext = context.expressionContext();
  QgsExpressionContext algContext = prevContext;

  algContext.appendScopes( createExpressionContext( parameters, context, mSource.get() ).takeScopes() );
  context.setExpressionContext( algContext );

  long count = mSource->featureCount();

  QgsFeature f;
  QgsFeatureIterator it = mSource->getFeatures( request(), sourceFlags() );

  double step = count > 0 ? 100.0 / count : 1;
  int current = 0;
  while ( it.nextFeature( f ) )
  {
    if ( feedback->isCanceled() )
    {
      break;
    }

    context.expressionContext().setFeature( f );
    const QgsFeatureList transformed = processFeature( f, context, feedback );
    for ( QgsFeature transformedFeature : transformed )
      sink->addFeature( transformedFeature, QgsFeatureSink::FastInsert );

    feedback->setProgress( current * step );
    current++;
  }

  mSource.reset();

  // probably not necessary - context's aren't usually recycled, but can't hurt
  context.setExpressionContext( prevContext );

  QVariantMap outputs;
  outputs.insert( QStringLiteral( "OUTPUT" ), dest );
  return outputs;
}
QgsExpressionContext QgsPointDisplacementRendererWidget::createExpressionContext() const
{
  QgsExpressionContext context;
  if ( mContext.expressionContext() )
    context = *mContext.expressionContext();
  else
    context.appendScopes( mContext.globalProjectAtlasMapLayerScopes( mLayer ) );
  QgsExpressionContextScope scope;
  scope.addVariable( QgsExpressionContextScope::StaticVariable( QgsExpressionContext::EXPR_CLUSTER_COLOR, "", true ) );
  scope.addVariable( QgsExpressionContextScope::StaticVariable( QgsExpressionContext::EXPR_CLUSTER_SIZE, 0, true ) );
  QList< QgsExpressionContextScope > scopes = mContext.additionalExpressionContextScopes();
  scopes << scope;
  Q_FOREACH ( const QgsExpressionContextScope &s, scopes )
  {
    context << new QgsExpressionContextScope( s );
  }
QgsExpressionContext QgsPointClusterRendererWidget::createExpressionContext() const
{
  QgsExpressionContext context;
  if ( mContext.expressionContext() )
    context = *mContext.expressionContext();
  else
    context.appendScopes( mContext.globalProjectAtlasMapLayerScopes( mLayer ) );
  QgsExpressionContextScope scope;
  scope.addVariable( QgsExpressionContextScope::StaticVariable( QgsExpressionContext::EXPR_CLUSTER_COLOR, "", true ) );
  scope.addVariable( QgsExpressionContextScope::StaticVariable( QgsExpressionContext::EXPR_CLUSTER_SIZE, 0, true ) );
  QList< QgsExpressionContextScope > scopes = mContext.additionalExpressionContextScopes();
  scopes << scope;
  const auto constScopes = scopes;
  for ( const QgsExpressionContextScope &s : constScopes )
  {
    context << new QgsExpressionContextScope( s );
  }
  return context;
}
void QgsSymbolLegendNode::exportSymbolToJson( const QgsLegendSettings &settings, const QgsRenderContext &context, QJsonObject &json ) const
{
  const QgsSymbol *s = mItem.symbol();
  if ( !s )
  {
    return;
  }

  QgsRenderContext ctx;
  ctx.setScaleFactor( settings.dpi() / 25.4 );
  ctx.setRendererScale( settings.mapScale() );
  ctx.setMapToPixel( QgsMapToPixel( 1 / ( settings.mmPerMapUnit() * ctx.scaleFactor() ) ) );
  ctx.setForceVectorOutput( true );

  // ensure that a minimal expression context is available
  QgsExpressionContext expContext = context.expressionContext();
  expContext.appendScopes( QgsExpressionContextUtils::globalProjectLayerScopes( nullptr ) );
  ctx.setExpressionContext( expContext );

  const QPixmap pix = QgsSymbolLayerUtils::symbolPreviewPixmap( mItem.symbol(), minimumIconSize(), 0, &ctx );
  QImage img( pix.toImage().convertToFormat( QImage::Format_ARGB32_Premultiplied ) );

  int opacity = 255;
  if ( QgsVectorLayer *vectorLayer = qobject_cast<QgsVectorLayer *>( layerNode()->layer() ) )
    opacity = ( 255 * vectorLayer->opacity() );

  if ( opacity != 255 )
  {
    QPainter painter;
    painter.begin( &img );
    painter.setCompositionMode( QPainter::CompositionMode_DestinationIn );
    painter.fillRect( pix.rect(), QColor( 0, 0, 0, opacity ) );
    painter.end();
  }

  QByteArray byteArray;
  QBuffer buffer( &byteArray );
  img.save( &buffer, "PNG" );
  const QString base64 = QString::fromLatin1( byteArray.toBase64().data() );
  json[ "icon" ] = base64;
}
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QgsFeatureIterator QgsVectorLayerUtils::getValuesIterator( const QgsVectorLayer *layer, const QString &fieldOrExpression, bool &ok, bool selectedOnly )
{
  std::unique_ptr<QgsExpression> expression;
  QgsExpressionContext context;

  int attrNum = layer->fields().lookupField( fieldOrExpression );
  if ( attrNum == -1 )
  {
    // try to use expression
    expression.reset( new QgsExpression( fieldOrExpression ) );
    context.appendScopes( QgsExpressionContextUtils::globalProjectLayerScopes( layer ) );

    if ( expression->hasParserError() || !expression->prepare( &context ) )
    {
      ok = false;
      return QgsFeatureIterator();
    }
  }

  QSet<QString> lst;
  if ( !expression )
    lst.insert( fieldOrExpression );
  else
    lst = expression->referencedColumns();

  QgsFeatureRequest request = QgsFeatureRequest()
                              .setFlags( ( expression && expression->needsGeometry() ) ?
                                         QgsFeatureRequest::NoFlags :
                                         QgsFeatureRequest::NoGeometry )
                              .setSubsetOfAttributes( lst, layer->fields() );

  ok = true;
  if ( !selectedOnly )
  {
    return layer->getFeatures( request );
  }
  else
  {
    return layer->getSelectedFeatures( request );
  }
}
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QList<QVariant> QgsVectorLayerUtils::getValues( const QgsVectorLayer *layer, const QString &fieldOrExpression, bool &ok, bool selectedOnly, QgsFeedback *feedback )
{
  QList<QVariant> values;
  QgsFeatureIterator fit = getValuesIterator( layer, fieldOrExpression, ok, selectedOnly );
  if ( ok )
  {
    std::unique_ptr<QgsExpression> expression;
    QgsExpressionContext context;

    int attrNum = layer->fields().lookupField( fieldOrExpression );
    if ( attrNum == -1 )
    {
      // use expression, already validated in the getValuesIterator() function
      expression.reset( new QgsExpression( fieldOrExpression ) );
      context.appendScopes( QgsExpressionContextUtils::globalProjectLayerScopes( layer ) );
    }

    QgsFeature f;
    while ( fit.nextFeature( f ) )
    {
      if ( expression )
      {
        context.setFeature( f );
        QVariant v = expression->evaluate( &context );
        values << v;
      }
      else
      {
        values << f.attribute( attrNum );
      }
      if ( feedback && feedback->isCanceled() )
      {
        ok = false;
        return values;
      }
    }
  }
  return values;
}
QSizeF QgsSymbolLegendNode::drawSymbol( const QgsLegendSettings &settings, ItemContext *ctx, double itemHeight ) const
{
  QgsSymbol *s = mItem.symbol();
  if ( !s )
  {
    return QSizeF();
  }

  // setup temporary render context
  QgsRenderContext context;
  context.setScaleFactor( settings.dpi() / 25.4 );
  context.setRendererScale( settings.mapScale() );
  context.setMapToPixel( QgsMapToPixel( 1 / ( settings.mmPerMapUnit() * context.scaleFactor() ) ) );
  context.setForceVectorOutput( true );
  context.setPainter( ctx ? ctx->painter : nullptr );

  if ( ctx && ctx->context )
  {
    context.setExpressionContext( ctx->context->expressionContext() );
  }
  else
  {
    // setup a minimal expression context
    QgsExpressionContext expContext;
    expContext.appendScopes( QgsExpressionContextUtils::globalProjectLayerScopes( nullptr ) );
    context.setExpressionContext( expContext );
  }

  //Consider symbol size for point markers
  double height = settings.symbolSize().height();
  double width = settings.symbolSize().width();

  //Center small marker symbols
  double widthOffset = 0;
  double heightOffset = 0;

  if ( QgsMarkerSymbol *markerSymbol = dynamic_cast<QgsMarkerSymbol *>( s ) )
  {
    // allow marker symbol to occupy bigger area if necessary
    double size = markerSymbol->size( context ) / context.scaleFactor();
    height = size;
    width = size;
    if ( width < settings.symbolSize().width() )
    {
      widthOffset = ( settings.symbolSize().width() - width ) / 2.0;
    }
    if ( height < settings.symbolSize().height() )
    {
      heightOffset = ( settings.symbolSize().height() - height ) / 2.0;
    }
  }

  if ( ctx && ctx->painter )
  {
    double currentXPosition = ctx->point.x();
    double currentYCoord = ctx->point.y() + ( itemHeight - settings.symbolSize().height() ) / 2;
    QPainter *p = ctx->painter;

    //setup painter scaling to dots so that raster symbology is drawn to scale
    double dotsPerMM = context.scaleFactor();

    int opacity = 255;
    if ( QgsVectorLayer *vectorLayer = qobject_cast<QgsVectorLayer *>( layerNode()->layer() ) )
      opacity = ( 255 * vectorLayer->opacity() );

    p->save();
    p->setRenderHint( QPainter::Antialiasing );
    p->translate( currentXPosition + widthOffset, currentYCoord + heightOffset );
    p->scale( 1.0 / dotsPerMM, 1.0 / dotsPerMM );
    if ( opacity != 255 && settings.useAdvancedEffects() )
    {
      //semi transparent layer, so need to draw symbol to an image (to flatten it first)
      //create image which is same size as legend rect, in case symbol bleeds outside its alloted space
      QSize tempImageSize( width * dotsPerMM, height * dotsPerMM );
      QImage tempImage = QImage( tempImageSize, QImage::Format_ARGB32 );
      tempImage.fill( Qt::transparent );
      QPainter imagePainter( &tempImage );
      context.setPainter( &imagePainter );
      s->drawPreviewIcon( &imagePainter, tempImageSize, &context );
      context.setPainter( ctx->painter );
      //reduce opacity of image
      imagePainter.setCompositionMode( QPainter::CompositionMode_DestinationIn );
      imagePainter.fillRect( tempImage.rect(), QColor( 0, 0, 0, opacity ) );
      imagePainter.end();
      //draw rendered symbol image
      p->drawImage( 0, 0, tempImage );
    }
    else
    {
      s->drawPreviewIcon( p, QSize( width * dotsPerMM, height * dotsPerMM ), &context );
    }

    if ( !mTextOnSymbolLabel.isEmpty() )
    {
      QFontMetricsF fm( mTextOnSymbolTextFormat.scaledFont( context ) );
      qreal yBaselineVCenter = ( height * dotsPerMM + fm.ascent() - fm.descent() ) / 2;
      QgsTextRenderer::drawText( QPointF( width * dotsPerMM / 2, yBaselineVCenter ), 0, QgsTextRenderer::AlignCenter,
                                 QStringList() << mTextOnSymbolLabel, context, mTextOnSymbolTextFormat );
    }

    p->restore();
  }

  return QSizeF( std::max( width + 2 * widthOffset, static_cast< double >( settings.symbolSize().width() ) ),
                 std::max( height + 2 * heightOffset, static_cast< double >( settings.symbolSize().height() ) ) );
}