[processing] Make buffer distance a dynamic property

Data defined buffer distance through the processing toolbox!

Author: nyalldawson

src/analysis/processing/qgsalgorithmbuffer.cpp

@@ -42,7 +42,12 @@ QString QgsBufferAlgorithm::group() const
 void QgsBufferAlgorithm::initAlgorithm( const QVariantMap & )
 {
   addParameter( new QgsProcessingParameterFeatureSource( QStringLiteral( "INPUT" ), QObject::tr( "Input layer" ) ) );
-  addParameter( new QgsProcessingParameterNumber( QStringLiteral( "DISTANCE" ), QObject::tr( "Distance" ), QgsProcessingParameterNumber::Double, 10 ) );
+
+  auto bufferParam = qgis::make_unique < QgsProcessingParameterNumber >( QStringLiteral( "DISTANCE" ), QObject::tr( "Distance" ), QgsProcessingParameterNumber::Double, 10 );
+  bufferParam->setIsDynamic( true );
+  bufferParam->setDynamicPropertyDefinition( QgsPropertyDefinition( QStringLiteral( "Distance" ), QObject::tr( "Buffer distance" ), QgsPropertyDefinition::Double ) );
+  bufferParam->setDynamicLayerParameterName( QStringLiteral( "INPUT" ) );
+  addParameter( bufferParam.release() );
   addParameter( new QgsProcessingParameterNumber( QStringLiteral( "SEGMENTS" ), QObject::tr( "Segments" ), QgsProcessingParameterNumber::Integer, 5, false, 1 ) );
 
   addParameter( new QgsProcessingParameterEnum( QStringLiteral( "END_CAP_STYLE" ), QObject::tr( "End cap style" ), QStringList() << QObject::tr( "Round" ) << QObject::tr( "Flat" ) << QObject::tr( "Square" ), false ) );
@@ -86,7 +91,14 @@ QVariantMap QgsBufferAlgorithm::processAlgorithm( const QVariantMap &parameters,
   double miterLimit = parameterAsDouble( parameters, QStringLiteral( "MITER_LIMIT" ), context );
   double bufferDistance = parameterAsDouble( parameters, QStringLiteral( "DISTANCE" ), context );
   bool dynamicBuffer = QgsProcessingParameters::isDynamic( parameters, QStringLiteral( "DISTANCE" ) );
-  const QgsProcessingParameterDefinition *distanceParamDef = parameterDefinition( QStringLiteral( "DISTANCE" ) );
+  QgsExpressionContext expressionContext;
+  QgsProperty bufferProperty;
+  if ( dynamicBuffer )
+  {
+    bufferProperty = parameters.value( QStringLiteral( "DISTANCE" ) ).value< QgsProperty >();
+    expressionContext = createExpressionContext( parameters, context, dynamic_cast< QgsProcessingFeatureSource * >( source.get() ) );
+    bufferProperty.prepare( expressionContext );
+  }
 
   long count = source->featureCount();
 
@@ -111,13 +123,14 @@ QVariantMap QgsBufferAlgorithm::processAlgorithm( const QVariantMap &parameters,
     QgsFeature out = f;
     if ( out.hasGeometry() )
     {
+      double distance =  bufferDistance;
       if ( dynamicBuffer )
       {
-        context.expressionContext().setFeature( f );
-        bufferDistance = QgsProcessingParameters::parameterAsDouble( distanceParamDef, parameters, context );
+        expressionContext.setFeature( f );
+        distance = bufferProperty.valueAsDouble( expressionContext, bufferDistance );
       }
 
-      QgsGeometry outputGeometry = f.geometry().buffer( bufferDistance, segments, endCapStyle, joinStyle, miterLimit );
+      QgsGeometry outputGeometry = f.geometry().buffer( distance, segments, endCapStyle, joinStyle, miterLimit );
       if ( !outputGeometry )
       {
         QgsMessageLog::logMessage( QObject::tr( "Error calculating buffer for feature %1" ).arg( f.id() ), QObject::tr( "Processing" ), QgsMessageLog::WARNING );

src/analysis/processing/qgsalgorithmextractbyattribute.cpp

@@ -168,7 +168,7 @@ QVariantMap QgsExtractByAttributeAlgorithm::processAlgorithm( const QVariantMap
     throw QgsProcessingException( expression.parserErrorString() );
   }
 
-  QgsExpressionContext expressionContext = createExpressionContext( parameters, context );
+  QgsExpressionContext expressionContext = createExpressionContext( parameters, context, dynamic_cast< QgsProcessingFeatureSource * >( source.get() ) );
 
   long count = source->featureCount();
 

src/analysis/processing/qgsalgorithmextractbyexpression.cpp

@@ -87,7 +87,7 @@ QVariantMap QgsExtractByExpressionAlgorithm::processAlgorithm( const QVariantMap
     throw QgsProcessingException( expression.parserErrorString() );
   }
 
-  QgsExpressionContext expressionContext = createExpressionContext( parameters, context );
+  QgsExpressionContext expressionContext = createExpressionContext( parameters, context, dynamic_cast< QgsProcessingFeatureSource * >( source.get() ) );
 
   long count = source->featureCount();