Rule based renderer exposes filter where clause

This filter can then be sent to the server to reduce the amount of fetched
features

python/core/symbology-ng/qgsrulebasedrendererv2.sip

@@ -105,7 +105,9 @@ class QgsRuleBasedRendererV2 : QgsFeatureRendererV2
         QDomElement save( QDomDocument& doc, QgsSymbolV2Map& symbolMap );
 
         //! prepare the rule for rendering and its children (build active children array)
-        bool startRender( QgsRenderContext& context, const QgsFields& fields );
+        bool startRender( QgsRenderContext& context, const QgsFields& fields ) /Deprecated/;
+        //! prepare the rule for rendering and its children (build active children array)
+        bool startRender( QgsRenderContext& context, const QgsFields& fields, QString& filter );
         //! get all used z-levels from this rule and children
         QSet<int> collectZLevels();
         //! assign normalized z-levels [0..N-1] for this rule's symbol for quick access during rendering

src/core/qgsvectorlayerrenderer.cpp

@@ -134,7 +134,7 @@ bool QgsVectorLayerRenderer::render()
     mContext.painter()->setCompositionMode( mFeatureBlendMode );
   }
 
-  mRendererV2->startRender( mContext, mFields );
+  QgsRenderOptions opts = mRendererV2->startRender( mContext, mFields );
 
   QgsRectangle requestExtent = mContext.extent();
   mRendererV2->modifyRequestExtent( requestExtent, mContext );
@@ -143,6 +143,11 @@ bool QgsVectorLayerRenderer::render()
                                      .setFilterRect( requestExtent )
                                      .setSubsetOfAttributes( mAttrNames, mFields );
 
+  if ( !opts.whereClause().isNull() )
+  {
+    featureRequest.setFilterExpression( opts.whereClause() );
+  }
+
   // enable the simplification of the geometries (Using the current map2pixel context) before send it to renderer engine.
   if ( mSimplifyGeometry )
   {

src/core/symbology-ng/qgsrendererv2.h

@@ -64,6 +64,9 @@ class CORE_EXPORT QgsSymbolV2LevelItem
 class CORE_EXPORT QgsRenderOptions
 {
   public:
+    QgsRenderOptions() {}
+    QgsRenderOptions( const QString& whereClause ) { mWhereClause = whereClause; }
+
     void setWhereClause( const QString& whereClause ) { mWhereClause = whereClause; }
     QString whereClause() { return mWhereClause; }
   private:

src/core/symbology-ng/qgsrulebasedrendererv2.cpp

@@ -390,6 +390,12 @@ void QgsRuleBasedRendererV2::Rule::toSld( QDomDocument& doc, QDomElement &elemen
 }
 
 bool QgsRuleBasedRendererV2::Rule::startRender( QgsRenderContext& context, const QgsFields& fields )
+{
+  QString filter;
+  return startRender( context, fields, filter );
+}
+
+bool QgsRuleBasedRendererV2::Rule::startRender( QgsRenderContext& context, const QgsFields& fields, QString& filter )
 {
   mActiveChildren.clear();
 
@@ -408,15 +414,37 @@ bool QgsRuleBasedRendererV2::Rule::startRender( QgsRenderContext& context, const
 
   // init children
   // build temporary list of active rules (usable with this scale)
+  QStringList subfilters;
   for ( RuleList::iterator it = mChildren.begin(); it != mChildren.end(); ++it )
   {
+    QString subfilter;
     Rule* rule = *it;
-    if ( rule->startRender( context, fields ) )
+    if ( rule->startRender( context, fields , subfilter ) )
     {
       // only add those which are active with current scale
       mActiveChildren.append( rule );
+      subfilters.append( subfilter );
     }
   }
+
+  // subfilters (on the same level) are joined with OR and finally joined with AND with their parent (this) filter
+  QString sf;
+  if ( subfilters.length() )
+    sf = subfilters.join( ") OR (" ).prepend( "(" ).append( ")" );
+
+  if ( isElse() )
+  {
+    if ( !sf.length() )
+      filter = "1";
+    else
+      filter = sf;
+  }
+  else if ( mFilterExp.length() && sf.length() )
+    filter = QString( "(%1) AND (%2)" ).arg( mFilterExp ).arg( sf );
+  else if ( mFilterExp.length() )
+    filter = mFilterExp;
+  else
+    filter = sf;
   return true;
 }
 
@@ -781,8 +809,9 @@ bool QgsRuleBasedRendererV2::renderFeature( QgsFeature& feature,
 
 QgsRenderOptions QgsRuleBasedRendererV2::startRender( QgsRenderContext& context, const QgsFields& fields )
 {
+  QString filter;
   // prepare active children
-  mRootRule->startRender( context, fields );
+  mRootRule->startRender( context, fields, filter );
 
   QSet<int> symbolZLevelsSet = mRootRule->collectZLevels();
   QList<int> symbolZLevels = symbolZLevelsSet.toList();
@@ -800,7 +829,7 @@ QgsRenderOptions QgsRuleBasedRendererV2::startRender( QgsRenderContext& context,
   }
 
   mRootRule->setNormZLevels( zLevelsToNormLevels );
-  return QgsRenderOptions();
+  return QgsRenderOptions( filter );
 }
 
 void QgsRuleBasedRendererV2::stopRender( QgsRenderContext& context )

src/core/symbology-ng/qgsrulebasedrendererv2.h

@@ -135,7 +135,9 @@ class CORE_EXPORT QgsRuleBasedRendererV2 : public QgsFeatureRendererV2
         QDomElement save( QDomDocument& doc, QgsSymbolV2Map& symbolMap );
 
         //! prepare the rule for rendering and its children (build active children array)
-        bool startRender( QgsRenderContext& context, const QgsFields& fields );
+        Q_DECL_DEPRECATED bool startRender( QgsRenderContext& context, const QgsFields& fields );
+        //! prepare the rule for rendering and its children (build active children array)
+        bool startRender( QgsRenderContext& context, const QgsFields& fields, QString& filter );
         //! get all used z-levels from this rule and children
         QSet<int> collectZLevels();
         //! assign normalized z-levels [0..N-1] for this rule's symbol for quick access during rendering