From a0e35a3893f44e8bfc19a12c835458c533217be5 Mon Sep 17 00:00:00 2001
From: Nyall Dawson <nyall.dawson@gmail.com>
Date: Thu, 13 Aug 2015 09:42:51 +1000
Subject: [PATCH] Switch some composer expressions to contexts

---
 python/core/composer/qgscomposeritem.sip   |   6 +
 python/core/qgsexpressioncontext.sip       |  50 +++++++
 src/app/composer/qgscomposeritemwidget.cpp |  13 ++
 src/app/composer/qgscomposeritemwidget.h   |   5 +
 src/app/composer/qgscompositionwidget.cpp  |  14 ++
 src/app/composer/qgscompositionwidget.h    |   2 +
 src/core/composer/qgsatlascomposition.cpp  |  40 ++++-
 src/core/composer/qgsatlascomposition.h    |   5 +-
 src/core/composer/qgscomposeritem.cpp      |  19 +++
 src/core/composer/qgscomposeritem.h        |   7 +
 src/core/composer/qgscomposerlabel.cpp     |  23 ++-
 src/core/qgsexpressioncontext.cpp          | 164 +++++++++++++++++++++
 src/core/qgsexpressioncontext.h            |  59 ++++++++
 src/ui/qgscomposeritemwidgetbase.ui        |  31 ++++
 src/ui/qgscompositionwidgetbase.ui         |  58 ++++++--
 15 files changed, 470 insertions(+), 26 deletions(-)

diff --git a/python/core/composer/qgscomposeritem.sip b/python/core/composer/qgscomposeritem.sip
index 9713e0fdbcb..b35c5cc6554 100644
--- a/python/core/composer/qgscomposeritem.sip
+++ b/python/core/composer/qgscomposeritem.sip
@@ -630,6 +630,12 @@ class QgsComposerItem : QgsComposerObject, QGraphicsRectItem
     */
     void setCurrentExportLayer( const int layerIdx = -1 );
 
+    /** Creates an expression context relating to the item's current state. The context includes
+     * scopes for global, project, composition, atlas and item properties.
+     * @note added in QGIS 2.12
+     */
+    QgsExpressionContext* createExpressionContext() const /Factory/;
+
   public slots:
     /** Sets the item rotation
      * @deprecated Use setItemRotation( double rotation ) instead
diff --git a/python/core/qgsexpressioncontext.sip b/python/core/qgsexpressioncontext.sip
index 142bef735de..15b15817306 100644
--- a/python/core/qgsexpressioncontext.sip
+++ b/python/core/qgsexpressioncontext.sip
@@ -404,6 +404,56 @@ class QgsExpressionContextUtils
      */
     static void setLayerVariables( QgsMapLayer* layer, const QgsStringMap variables );
 
+    /** Creates a new scope which contains variables and functions relating to a QgsComposition.
+     * For instance, number of pages and page sizes.
+     * @param composition source composition
+     */
+    static QgsExpressionContextScope* compositionScope( const QgsComposition *composition ) /Factory/;
+
+    /** Sets a composition context variable. This variable will be contained within scopes retrieved via
+     * compositionScope().
+     * @param composition target composition
+     * @param name variable name
+     * @param value variable value
+     * @see setCompositionVariables()
+     * @see compositionScope()
+     */
+    static void setCompositionVariable( QgsComposition* composition, const QString& name, const QVariant& value );
+
+    /** Sets all composition context variables. Existing composition variables will be removed and replaced
+     * with the variables specified.
+     * @param composition target composition
+     * @param variables new set of layer variables
+     * @see setCompositionVariable()
+     * @see compositionScope()
+     */
+    static void setCompositionVariables( QgsComposition* composition, const QgsStringMap variables );
+
+    /** Creates a new scope which contains variables and functions relating to a QgsComposerItem.
+     * For instance, item size and position.
+     * @param composerItem source composer item
+     */
+    static QgsExpressionContextScope* composerItemScope( const QgsComposerItem *composerItem ) /Factory/;
+
+    /** Sets a composer item context variable. This variable will be contained within scopes retrieved via
+     * composerItemScope().
+     * @param composerItem target composer item
+     * @param name variable name
+     * @param value variable value
+     * @see setComposerItemVariables()
+     * @see composerItemScope()
+     */
+    static void setComposerItemVariable( QgsComposerItem* composerItem, const QString& name, const QVariant& value );
+
+    /** Sets all composition context variables. Existing compositoin variables will be removed and replaced
+     * with the variables specified.
+     * @param composerItem target composer item
+     * @param variables new set of layer variables
+     * @see setComposerItemVariable()
+     * @see composerItemScope()
+     */
+    static void setComposerItemVariables( QgsComposerItem* composerItem, const QgsStringMap variables );
+
     /** Registers all known core functions provided by QgsExpressionContextScope objects.
      */
     static void registerContextFunctions();
diff --git a/src/app/composer/qgscomposeritemwidget.cpp b/src/app/composer/qgscomposeritemwidget.cpp
index 2d88eaee48e..43a860746bf 100644
--- a/src/app/composer/qgscomposeritemwidget.cpp
+++ b/src/app/composer/qgscomposeritemwidget.cpp
@@ -22,6 +22,7 @@
 #include "qgscomposition.h"
 #include "qgspoint.h"
 #include "qgsdatadefinedbutton.h"
+#include "qgsexpressioncontext.h"
 #include <QColorDialog>
 #include <QPen>
 
@@ -140,6 +141,13 @@ QgsComposerItemWidget::QgsComposerItemWidget( QWidget* parent, QgsComposerItem*
 
   connect( mTransparencySlider, SIGNAL( valueChanged( int ) ), mTransparencySpnBx, SLOT( setValue( int ) ) );
 
+  QgsExpressionContext* context = mItem->createExpressionContext();
+  mVariableEditor->setContext( context );
+  mVariableEditor->setEditableScopeIndex( context->scopeCount() - 1 );
+  delete context;
+
+  connect( mVariableEditor, SIGNAL( scopeChanged() ), this, SLOT( variablesChanged() ) );
+
   //connect atlas signals to data defined buttons
   QgsAtlasComposition* atlas = atlasComposition();
   if ( atlas )
@@ -260,6 +268,11 @@ void QgsComposerItemWidget::changeItemPosition()
   mItem->endCommand();
 }
 
+void QgsComposerItemWidget::variablesChanged()
+{
+  QgsExpressionContextUtils::setComposerItemVariables( mItem, mVariableEditor->variablesInActiveScope() );
+}
+
 QgsComposerItem::ItemPositionMode QgsComposerItemWidget::positionMode() const
 {
   if ( mUpperLeftCheckBox->checkState() == Qt::Checked )
diff --git a/src/app/composer/qgscomposeritemwidget.h b/src/app/composer/qgscomposeritemwidget.h
index 0f2bbc3bc98..f5e884c9271 100644
--- a/src/app/composer/qgscomposeritemwidget.h
+++ b/src/app/composer/qgscomposeritemwidget.h
@@ -139,6 +139,11 @@ class QgsComposerItemWidget: public QgsComposerItemBaseWidget, private Ui::QgsCo
 //    void changeItemTransparency( int value );
     void changeItemPosition();
 
+  private slots:
+
+    void variablesChanged();
+
+
 };
 
 #endif //QGSCOMPOSERITEMWIDGET_H
diff --git a/src/app/composer/qgscompositionwidget.cpp b/src/app/composer/qgscompositionwidget.cpp
index 13c072ac7ae..2a810839478 100644
--- a/src/app/composer/qgscompositionwidget.cpp
+++ b/src/app/composer/qgscompositionwidget.cpp
@@ -22,6 +22,7 @@
 #include "qgsstylev2.h"
 #include "qgssymbolv2selectordialog.h"
 #include "qgssymbollayerv2utils.h"
+#include "qgsexpressioncontext.h"
 #include <QColorDialog>
 #include <QWidget>
 #include <QPrinter> //for screen resolution
@@ -44,6 +45,14 @@ QgsCompositionWidget::QgsCompositionWidget( QWidget* parent, QgsComposition* c )
   //read with/height from composition and find suitable entries to display
   displayCompositionWidthHeight();
 
+  mVariableEditor->context()->appendScope( QgsExpressionContextUtils::globalScope() );
+  mVariableEditor->context()->appendScope( QgsExpressionContextUtils::projectScope() );
+  mVariableEditor->context()->appendScope( QgsExpressionContextUtils::compositionScope( mComposition ) );
+  mVariableEditor->reloadContext();
+  mVariableEditor->setEditableScopeIndex( 2 );
+
+  connect( mVariableEditor, SIGNAL( scopeChanged() ), this, SLOT( variablesChanged() ) );
+
   if ( mComposition )
   {
     mNumPagesSpinBox->setValue( mComposition->numPages() );
@@ -170,6 +179,11 @@ void QgsCompositionWidget::populateDataDefinedButtons()
   mPaperOrientationDDBtn->blockSignals( false );
 }
 
+void QgsCompositionWidget::variablesChanged()
+{
+  QgsExpressionContextUtils::setCompositionVariables( mComposition, mVariableEditor->variablesInActiveScope() );
+}
+
 void QgsCompositionWidget::setDataDefinedProperty( const QgsDataDefinedButton* ddBtn, QgsComposerObject::DataDefinedProperty property )
 {
   if ( !mComposition )
diff --git a/src/app/composer/qgscompositionwidget.h b/src/app/composer/qgscompositionwidget.h
index 023a48bc2bd..368e9ecc193 100644
--- a/src/app/composer/qgscompositionwidget.h
+++ b/src/app/composer/qgscompositionwidget.h
@@ -83,6 +83,8 @@ class QgsCompositionWidget: public QWidget, private Ui::QgsCompositionWidgetBase
     /** Initializes data defined buttons to current atlas coverage layer*/
     void populateDataDefinedButtons();
 
+    void variablesChanged();
+
   private:
     QgsComposition* mComposition;
     QMap<QString, QgsCompositionPaper> mPaperMap;
diff --git a/src/core/composer/qgsatlascomposition.cpp b/src/core/composer/qgsatlascomposition.cpp
index ca6dc99db21..8fc05919ad8 100644
--- a/src/core/composer/qgsatlascomposition.cpp
+++ b/src/core/composer/qgsatlascomposition.cpp
@@ -27,6 +27,7 @@
 #include "qgsmaplayerregistry.h"
 #include "qgsproject.h"
 #include "qgsmessagelog.h"
+#include "qgsexpressioncontext.h"
 
 QgsAtlasComposition::QgsAtlasComposition( QgsComposition* composition )
     : mComposition( composition )
@@ -218,6 +219,8 @@ int QgsAtlasComposition::updateFeatures()
     return 0;
   }
 
+  QgsExpressionContext expressionContext = createExpressionContext();
+
   updateFilenameExpression();
 
   // select all features with all attributes
@@ -248,7 +251,7 @@ int QgsAtlasComposition::updateFeatures()
     {
       nameExpression.reset( 0 );
     }
-    nameExpression->prepare( mCoverageLayer->pendingFields() );
+    nameExpression->prepare( &expressionContext );
   }
 
   // We cannot use nextFeature() directly since the feature pointer is rewinded by the rendering process
@@ -260,10 +263,12 @@ int QgsAtlasComposition::updateFeatures()
 
   while ( fit.nextFeature( feat ) )
   {
+    expressionContext.setFeature( feat );
+
     QString pageName;
     if ( !nameExpression.isNull() )
     {
-      QVariant result = nameExpression->evaluate( &feat, mCoverageLayer->fields() );
+      QVariant result = nameExpression->evaluate( &expressionContext );
       if ( nameExpression->hasEvalError() )
       {
         QgsMessageLog::logMessage( tr( "Atlas name eval error: %1" ).arg( nameExpression->evalErrorString() ), tr( "Composer" ) );
@@ -446,13 +451,15 @@ bool QgsAtlasComposition::prepareForFeature( const int featureI, const bool upda
   // retrieve the next feature, based on its id
   mCoverageLayer->getFeatures( QgsFeatureRequest().setFilterFid( mFeatureIds[ featureI ].first ) ).nextFeature( mCurrentFeature );
 
+  QgsExpressionContext expressionContext = createExpressionContext();
+
   QgsExpression::setSpecialColumn( "$atlasfeatureid", mCurrentFeature.id() );
   QgsExpression::setSpecialColumn( "$atlasgeometry", QVariant::fromValue( *mCurrentFeature.constGeometry() ) );
   QgsExpression::setSpecialColumn( "$atlasfeature", QVariant::fromValue( mCurrentFeature ) );
   QgsExpression::setSpecialColumn( "$feature", QVariant(( int )featureI + 1 ) );
 
   // generate filename for current feature
-  if ( !evalFeatureFilename() )
+  if ( !evalFeatureFilename( expressionContext ) )
   {
     //error evaluating filename
     return false;
@@ -820,6 +827,23 @@ bool QgsAtlasComposition::setFilenamePattern( const QString& pattern )
   return updateFilenameExpression();
 }
 
+QgsExpressionContext QgsAtlasComposition::createExpressionContext()
+{
+  QgsExpressionContext expressionContext;
+  expressionContext << QgsExpressionContextUtils::globalScope()
+  << QgsExpressionContextUtils::projectScope();
+  if ( mComposition )
+    expressionContext << QgsExpressionContextUtils::compositionScope( mComposition );
+
+  expressionContext << new QgsExpressionContextScope( "Atlas" );
+  if ( mCoverageLayer )
+    expressionContext.lastScope()->setFields( mCoverageLayer->fields() );
+  if ( mComposition->atlasMode() != QgsComposition::AtlasOff )
+    expressionContext.lastScope()->setFeature( mCurrentFeature );
+
+  return expressionContext;
+}
+
 bool QgsAtlasComposition::updateFilenameExpression()
 {
   if ( !mCoverageLayer )
@@ -827,7 +851,7 @@ bool QgsAtlasComposition::updateFilenameExpression()
     return false;
   }
 
-  const QgsFields& fields = mCoverageLayer->fields();
+  QgsExpressionContext expressionContext = createExpressionContext();
 
   if ( mFilenamePattern.size() > 0 )
   {
@@ -841,23 +865,23 @@ bool QgsAtlasComposition::updateFilenameExpression()
     }
 
     // prepare the filename expression
-    mFilenameExpr->prepare( fields );
+    mFilenameExpr->prepare( &expressionContext );
   }
 
   //if atlas preview is currently enabled, regenerate filename for current feature
   if ( mComposition->atlasMode() == QgsComposition::PreviewAtlas )
   {
-    evalFeatureFilename();
+    evalFeatureFilename( expressionContext );
   }
   return true;
 }
 
-bool QgsAtlasComposition::evalFeatureFilename()
+bool QgsAtlasComposition::evalFeatureFilename( const QgsExpressionContext &context )
 {
   //generate filename for current atlas feature
   if ( mFilenamePattern.size() > 0 && !mFilenameExpr.isNull() )
   {
-    QVariant filenameRes = mFilenameExpr->evaluate( &mCurrentFeature, mCoverageLayer->fields() );
+    QVariant filenameRes = mFilenameExpr->evaluate( &context );
     if ( mFilenameExpr->hasEvalError() )
     {
       QgsMessageLog::logMessage( tr( "Atlas filename evaluation error: %1" ).arg( mFilenameExpr->evalErrorString() ), tr( "Composer" ) );
diff --git a/src/core/composer/qgsatlascomposition.h b/src/core/composer/qgsatlascomposition.h
index e104c2f3e84..fd98fc33604 100644
--- a/src/core/composer/qgsatlascomposition.h
+++ b/src/core/composer/qgsatlascomposition.h
@@ -29,6 +29,7 @@ class QgsComposerMap;
 class QgsComposition;
 class QgsVectorLayer;
 class QgsExpression;
+class QgsExpressionContext;
 
 /** \ingroup MapComposer
  * Class used to render an Atlas, iterating over geometry features.
@@ -338,7 +339,7 @@ class CORE_EXPORT QgsAtlasComposition : public QObject
     /** Evaluates filename for current feature
      * @returns true if feature filename was successfully evaluated
     */
-    bool evalFeatureFilename();
+    bool evalFeatureFilename( const QgsExpressionContext &context );
 
     QgsComposition* mComposition;
 
@@ -396,6 +397,8 @@ class CORE_EXPORT QgsAtlasComposition : public QObject
     //computes the extent of the current feature, in the crs of the specified map
     void computeExtent( QgsComposerMap *map );
 
+    QgsExpressionContext createExpressionContext();
+
     //list of predefined scales
     QVector<qreal> mPredefinedScales;
 };
diff --git a/src/core/composer/qgscomposeritem.cpp b/src/core/composer/qgscomposeritem.cpp
index 003d9e01e6c..24d41cc6356 100644
--- a/src/core/composer/qgscomposeritem.cpp
+++ b/src/core/composer/qgscomposeritem.cpp
@@ -40,6 +40,7 @@
 #include "qgslogger.h"
 #include "qgssymbollayerv2utils.h" //for pointOnLineWithDistance
 #include "qgsmaprenderer.h" //for getCompositionMode
+#include "qgsexpressioncontext.h"
 
 #include <cmath>
 
@@ -846,6 +847,24 @@ bool QgsComposerItem::shouldDrawItem() const
   return !mEvaluatedExcludeFromExports;
 }
 
+QgsExpressionContext* QgsComposerItem::createExpressionContext() const
+{
+  QgsExpressionContext* context = new QgsExpressionContext();
+  context->appendScope( QgsExpressionContextUtils::globalScope() );
+  context->appendScope( QgsExpressionContextUtils::projectScope() );
+  if ( mComposition )
+  {
+    context->appendScope( QgsExpressionContextUtils::compositionScope( mComposition ) );
+    if ( mComposition->atlasComposition().enabled() )
+    {
+      context->appendScope( QgsExpressionContextUtils::atlasScope( &mComposition->atlasComposition() ) );
+    }
+  }
+
+  context->appendScope( QgsExpressionContextUtils::composerItemScope( this ) );
+  return context;
+}
+
 void QgsComposerItem::drawBackground( QPainter* p )
 {
   if ( mBackground && p )
diff --git a/src/core/composer/qgscomposeritem.h b/src/core/composer/qgscomposeritem.h
index ab82f67815b..312b2fc1756 100644
--- a/src/core/composer/qgscomposeritem.h
+++ b/src/core/composer/qgscomposeritem.h
@@ -31,6 +31,7 @@ class QGraphicsLineItem;
 class QgsComposerItemGroup;
 class QgsDataDefined;
 class QgsComposition;
+class QgsExpressionContext;
 
 /** \ingroup MapComposer
  * A item that forms part of a map composition.
@@ -582,6 +583,12 @@ class CORE_EXPORT QgsComposerItem: public QgsComposerObject, public QGraphicsRec
     */
     virtual void setCurrentExportLayer( const int layerIdx = -1 ) { mCurrentExportLayer = layerIdx; }
 
+    /** Creates an expression context relating to the item's current state. The context includes
+     * scopes for global, project, composition, atlas and item properties.
+     * @note added in QGIS 2.12
+     */
+    QgsExpressionContext* createExpressionContext() const;
+
   public slots:
     /** Sets the item rotation
      * @deprecated Use setItemRotation( double rotation ) instead
diff --git a/src/core/composer/qgscomposerlabel.cpp b/src/core/composer/qgscomposerlabel.cpp
index 897e3518080..1694a43109b 100644
--- a/src/core/composer/qgscomposerlabel.cpp
+++ b/src/core/composer/qgscomposerlabel.cpp
@@ -25,6 +25,7 @@
 #include "qgsproject.h"
 #include "qgsdistancearea.h"
 #include "qgsfontutils.h"
+#include "qgsexpressioncontext.h"
 
 #include "qgswebview.h"
 #include "qgswebframe.h"
@@ -269,19 +270,16 @@ void QgsComposerLabel::refreshExpressionContext()
   if ( !mComposition )
     return;
 
+  QgsVectorLayer* layer = 0;
   if ( mComposition->atlasComposition().enabled() )
   {
-    mExpressionLayer = mComposition->atlasComposition().coverageLayer();
-    if ( mComposition->atlasMode() != QgsComposition::AtlasOff )
-    {
-      mExpressionFeature.reset( new QgsFeature( mComposition->atlasComposition().feature() ) );
-    }
+    layer = mComposition->atlasComposition().coverageLayer();
   }
 
   //setup distance area conversion
-  if ( mExpressionLayer )
+  if ( layer )
   {
-    mDistanceArea->setSourceCrs( mExpressionLayer->crs().srsid() );
+    mDistanceArea->setSourceCrs( layer->crs().srsid() );
   }
   else
   {
@@ -300,7 +298,16 @@ QString QgsComposerLabel::displayText() const
   replaceDateText( displayText );
   QMap<QString, QVariant> subs = mSubstitutions;
   subs[ "$page" ] = QVariant(( int )mComposition->itemPageNumber( this ) + 1 );
-  return QgsExpression::replaceExpressionText( displayText, mExpressionFeature.data(), mExpressionLayer, &subs, mDistanceArea );
+
+  QScopedPointer<QgsExpressionContext> context( createExpressionContext() );
+  //overwrite layer/feature if they have been set via setExpressionContext
+  //TODO remove when setExpressionContext is removed
+  if ( mExpressionFeature.data() )
+    context->setFeature( *mExpressionFeature.data() );
+  if ( mExpressionLayer )
+    context->setFields( mExpressionLayer->fields() );
+
+  return QgsExpression::replaceExpressionText( displayText, context.data(), &subs, mDistanceArea );
 }
 
 void QgsComposerLabel::replaceDateText( QString& text ) const
diff --git a/src/core/qgsexpressioncontext.cpp b/src/core/qgsexpressioncontext.cpp
index 0e7e10fe91a..1d17f865530 100644
--- a/src/core/qgsexpressioncontext.cpp
+++ b/src/core/qgsexpressioncontext.cpp
@@ -22,6 +22,9 @@
 #include "qgsproject.h"
 #include "qgssymbollayerv2utils.h"
 #include "qgsgeometry.h"
+#include "qgscomposition.h"
+#include "qgscomposeritem.h"
+#include "qgsatlascomposition.h"
 #include <QSettings>
 #include <QDir>
 
@@ -586,6 +589,167 @@ void QgsExpressionContextUtils::setLayerVariables( QgsMapLayer* layer, const Qgs
   layer->setCustomProperty( "variableValues", variableValues );
 }
 
+QgsExpressionContextScope *QgsExpressionContextUtils::compositionScope( const QgsComposition *composition )
+{
+  QgsExpressionContextScope* scope = new QgsExpressionContextScope( QObject::tr( "Composition" ) );
+  if ( !composition )
+    return scope;
+
+  //add variables defined in composition properties
+  QStringList variableNames = composition->customProperty( "variableNames" ).toStringList();
+  QStringList variableValues = composition->customProperty( "variableValues" ).toStringList();
+
+  int varIndex = 0;
+  foreach ( QString variableName, variableNames )
+  {
+    if ( varIndex >= variableValues.length() )
+    {
+      break;
+    }
+
+    QVariant varValue = variableValues.at( varIndex );
+    varIndex++;
+    scope->setVariable( variableName, varValue );
+  }
+
+  //add known composition context variables
+  scope->addVariable( QgsExpressionContextScope::StaticVariable( "composer_numpages", composition->numPages(), true ) );
+  scope->addVariable( QgsExpressionContextScope::StaticVariable( "composer_page_height", composition->paperHeight(), true ) );
+  scope->addVariable( QgsExpressionContextScope::StaticVariable( "composer_page_width", composition->paperWidth(), true ) );
+  scope->addVariable( QgsExpressionContextScope::StaticVariable( "composer_dpi", composition->printResolution(), true ) );
+
+  return scope;
+}
+
+void QgsExpressionContextUtils::setCompositionVariable( QgsComposition* composition, const QString& name, const QVariant& value )
+{
+  if ( !composition )
+    return;
+
+  //write variable to composition
+  QStringList variableNames = composition->customProperty( "variableNames" ).toStringList();
+  QStringList variableValues = composition->customProperty( "variableValues" ).toStringList();
+
+  variableNames << name;
+  variableValues << value.toString();
+
+  composition->setCustomProperty( "variableNames", variableNames );
+  composition->setCustomProperty( "variableValues", variableValues );
+}
+
+void QgsExpressionContextUtils::setCompositionVariables( QgsComposition* composition, const QgsStringMap variables )
+{
+  if ( !composition )
+    return;
+
+  QStringList variableNames;
+  QStringList variableValues;
+
+  Q_FOREACH ( QString variable, variables.keys() )
+  {
+    variableNames << variable;
+    variableValues << variables.value( variable );
+  }
+
+  composition->setCustomProperty( "variableNames", variableNames );
+  composition->setCustomProperty( "variableValues", variableValues );
+}
+
+QgsExpressionContextScope* QgsExpressionContextUtils::atlasScope( const QgsAtlasComposition* atlas )
+{
+  QgsExpressionContextScope* scope = new QgsExpressionContextScope( QObject::tr( "Atlas" ) );
+  if ( !atlas )
+    return scope;
+
+  //add known atlas variables
+  scope->addVariable( QgsExpressionContextScope::StaticVariable( "atlas_numpages", atlas->numFeatures(), true ) );
+  scope->addVariable( QgsExpressionContextScope::StaticVariable( "atlas_page", atlas->currentFeatureNumber() + 1, true ) );
+  scope->addVariable( QgsExpressionContextScope::StaticVariable( "atlas_filename", atlas->currentFilename(), true ) );
+  scope->addVariable( QgsExpressionContextScope::StaticVariable( "atlas_pagename", atlas->currentPageName(), true ) );
+
+  if ( atlas->enabled() && atlas->coverageLayer() )
+  {
+    scope->setFields( atlas->coverageLayer()->fields() );
+  }
+
+  if ( atlas->enabled() )
+  {
+    QgsFeature atlasFeature = atlas->feature();
+    scope->setFeature( atlasFeature );
+    scope->addVariable( QgsExpressionContextScope::StaticVariable( "atlas_featureid", atlasFeature.id(), true ) );
+  }
+
+  return scope;
+}
+
+QgsExpressionContextScope *QgsExpressionContextUtils::composerItemScope( const QgsComposerItem *composerItem )
+{
+  QgsExpressionContextScope* scope = new QgsExpressionContextScope( QObject::tr( "Composer Item" ) );
+  if ( !composerItem )
+    return scope;
+
+  //add variables defined in composer item properties
+  QStringList variableNames = composerItem->customProperty( "variableNames" ).toStringList();
+  QStringList variableValues = composerItem->customProperty( "variableValues" ).toStringList();
+
+  int varIndex = 0;
+  foreach ( QString variableName, variableNames )
+  {
+    if ( varIndex >= variableValues.length() )
+    {
+      break;
+    }
+
+    QVariant varValue = variableValues.at( varIndex );
+    varIndex++;
+    scope->setVariable( variableName, varValue );
+  }
+
+  //add known composer item context variables
+  scope->addVariable( QgsExpressionContextScope::StaticVariable( "item_id", composerItem->id(), true ) );
+  scope->addVariable( QgsExpressionContextScope::StaticVariable( "item_uuid", composerItem->uuid(), true ) );
+  scope->addVariable( QgsExpressionContextScope::StaticVariable( "item_left", composerItem->sceneBoundingRect().left(), true ) );
+  scope->addVariable( QgsExpressionContextScope::StaticVariable( "item_top", composerItem->sceneBoundingRect().top(), true ) );
+  scope->addVariable( QgsExpressionContextScope::StaticVariable( "item_width", composerItem->sceneBoundingRect().width(), true ) );
+  scope->addVariable( QgsExpressionContextScope::StaticVariable( "item_height", composerItem->sceneBoundingRect().height(), true ) );
+
+  return scope;
+}
+
+void QgsExpressionContextUtils::setComposerItemVariable( QgsComposerItem* composerItem, const QString& name, const QVariant& value )
+{
+  if ( !composerItem )
+    return;
+
+  //write variable to composer item
+  QStringList variableNames = composerItem->customProperty( "variableNames" ).toStringList();
+  QStringList variableValues = composerItem->customProperty( "variableValues" ).toStringList();
+
+  variableNames << name;
+  variableValues << value.toString();
+
+  composerItem->setCustomProperty( "variableNames", variableNames );
+  composerItem->setCustomProperty( "variableValues", variableValues );
+}
+
+void QgsExpressionContextUtils::setComposerItemVariables( QgsComposerItem* composerItem, const QgsStringMap variables )
+{
+  if ( !composerItem )
+    return;
+
+  QStringList variableNames;
+  QStringList variableValues;
+
+  Q_FOREACH ( QString variable, variables.keys() )
+  {
+    variableNames << variable;
+    variableValues << variables.value( variable );
+  }
+
+  composerItem->setCustomProperty( "variableNames", variableNames );
+  composerItem->setCustomProperty( "variableValues", variableValues );
+}
+
 QgsExpressionContext QgsExpressionContextUtils::createFeatureBasedContext( const QgsFeature &feature, const QgsFields &fields )
 {
   QgsExpressionContextScope* scope = new QgsExpressionContextScope();
diff --git a/src/core/qgsexpressioncontext.h b/src/core/qgsexpressioncontext.h
index 53d8d015327..a9c7b974442 100644
--- a/src/core/qgsexpressioncontext.h
+++ b/src/core/qgsexpressioncontext.h
@@ -24,6 +24,9 @@
 
 class QgsExpression;
 class QgsMapLayer;
+class QgsComposition;
+class QgsComposerItem;
+class QgsAtlasComposition;
 
 /** \ingroup core
  * \class QgsScopedExpressionFunction
@@ -430,6 +433,62 @@ class CORE_EXPORT QgsExpressionContextUtils
      */
     static void setLayerVariables( QgsMapLayer* layer, const QgsStringMap variables );
 
+    /** Creates a new scope which contains variables and functions relating to a QgsComposition.
+     * For instance, number of pages and page sizes.
+     * @param composition source composition
+     */
+    static QgsExpressionContextScope* compositionScope( const QgsComposition *composition );
+
+    /** Sets a composition context variable. This variable will be contained within scopes retrieved via
+     * compositionScope().
+     * @param composition target composition
+     * @param name variable name
+     * @param value variable value
+     * @see setCompositionVariables()
+     * @see compositionScope()
+     */
+    static void setCompositionVariable( QgsComposition* composition, const QString& name, const QVariant& value );
+
+    /** Sets all composition context variables. Existing composition variables will be removed and replaced
+     * with the variables specified.
+     * @param composition target composition
+     * @param variables new set of layer variables
+     * @see setCompositionVariable()
+     * @see compositionScope()
+     */
+    static void setCompositionVariables( QgsComposition* composition, const QgsStringMap variables );
+
+    /** Creates a new scope which contains variables and functions relating to a QgsAtlasComposition.
+     * For instance, current page name and number.
+     * @param atlas source atlas
+     */
+    static QgsExpressionContextScope* atlasScope( const QgsAtlasComposition* atlas );
+
+    /** Creates a new scope which contains variables and functions relating to a QgsComposerItem.
+     * For instance, item size and position.
+     * @param composerItem source composer item
+     */
+    static QgsExpressionContextScope* composerItemScope( const QgsComposerItem *composerItem );
+
+    /** Sets a composer item context variable. This variable will be contained within scopes retrieved via
+     * composerItemScope().
+     * @param composerItem target composer item
+     * @param name variable name
+     * @param value variable value
+     * @see setComposerItemVariables()
+     * @see composerItemScope()
+     */
+    static void setComposerItemVariable( QgsComposerItem* composerItem, const QString& name, const QVariant& value );
+
+    /** Sets all composition context variables. Existing compositoin variables will be removed and replaced
+     * with the variables specified.
+     * @param composerItem target composer item
+     * @param variables new set of layer variables
+     * @see setComposerItemVariable()
+     * @see composerItemScope()
+     */
+    static void setComposerItemVariables( QgsComposerItem* composerItem, const QgsStringMap variables );
+
     /** Helper function for creating an expression context which contains just a feature and fields
      * collection. Generally this method should not be used as the created context does not include
      * standard scopes such as the global and project scopes.
diff --git a/src/ui/qgscomposeritemwidgetbase.ui b/src/ui/qgscomposeritemwidgetbase.ui
index bcc6c014400..8d50fe4b467 100644
--- a/src/ui/qgscomposeritemwidgetbase.ui
+++ b/src/ui/qgscomposeritemwidgetbase.ui
@@ -703,6 +703,25 @@
      </layout>
     </widget>
    </item>
+   <item>
+    <widget class="QgsCollapsibleGroupBox" name="groupBox_3">
+     <property name="title">
+      <string>Variables</string>
+     </property>
+     <layout class="QVBoxLayout" name="verticalLayout_4">
+      <item>
+       <widget class="QgsVariableEditorWidget" name="mVariableEditor" native="true">
+        <property name="minimumSize">
+         <size>
+          <width>0</width>
+          <height>200</height>
+         </size>
+        </property>
+       </widget>
+      </item>
+     </layout>
+    </widget>
+   </item>
    <item>
     <spacer name="verticalSpacer">
      <property name="orientation">
@@ -759,6 +778,18 @@
    <extends>QComboBox</extends>
    <header>qgsblendmodecombobox.h</header>
   </customwidget>
+  <customwidget>
+   <class>QgsCollapsibleGroupBox</class>
+   <extends>QGroupBox</extends>
+   <header>qgscollapsiblegroupbox.h</header>
+   <container>1</container>
+  </customwidget>
+  <customwidget>
+   <class>QgsVariableEditorWidget</class>
+   <extends>QWidget</extends>
+   <header location="global">qgsvariableeditorwidget.h</header>
+   <container>1</container>
+  </customwidget>
  </customwidgets>
  <tabstops>
   <tabstop>mGeneralOptionsGroupBox</tabstop>
diff --git a/src/ui/qgscompositionwidgetbase.ui b/src/ui/qgscompositionwidgetbase.ui
index 2529a32a83e..9b6603770ca 100644
--- a/src/ui/qgscompositionwidgetbase.ui
+++ b/src/ui/qgscompositionwidgetbase.ui
@@ -23,7 +23,16 @@
    <property name="spacing">
     <number>0</number>
    </property>
-   <property name="margin">
+   <property name="leftMargin">
+    <number>0</number>
+   </property>
+   <property name="topMargin">
+    <number>0</number>
+   </property>
+   <property name="rightMargin">
+    <number>0</number>
+   </property>
+   <property name="bottomMargin">
     <number>0</number>
    </property>
    <item>
@@ -50,9 +59,9 @@
       <property name="geometry">
        <rect>
         <x>0</x>
-        <y>0</y>
+        <y>-337</y>
         <width>327</width>
-        <height>586</height>
+        <height>841</height>
        </rect>
       </property>
       <layout class="QVBoxLayout" name="verticalLayout_2">
@@ -137,7 +146,7 @@
               <property name="maximum">
                <double>99999.000000000000000</double>
               </property>
-              <property name="showClearButton">
+              <property name="showClearButton" stdset="0">
                <bool>false</bool>
               </property>
              </widget>
@@ -180,7 +189,7 @@
               <property name="maximum">
                <double>99999.000000000000000</double>
               </property>
-              <property name="showClearButton">
+              <property name="showClearButton" stdset="0">
                <bool>false</bool>
               </property>
              </widget>
@@ -234,7 +243,7 @@
               <property name="minimum">
                <number>1</number>
               </property>
-              <property name="showClearButton">
+              <property name="showClearButton" stdset="0">
                <bool>false</bool>
               </property>
              </widget>
@@ -317,7 +326,7 @@
             <property name="maximum">
              <number>3000</number>
             </property>
-            <property name="showClearButton">
+            <property name="showClearButton" stdset="0">
              <bool>false</bool>
             </property>
            </widget>
@@ -406,7 +415,7 @@
             <property name="maximum">
              <double>9999.000000000000000</double>
             </property>
-            <property name="showClearButton">
+            <property name="showClearButton" stdset="0">
              <bool>false</bool>
             </property>
            </widget>
@@ -466,7 +475,7 @@
             <property name="maximum">
              <number>200</number>
             </property>
-            <property name="showClearButton">
+            <property name="showClearButton" stdset="0">
              <bool>false</bool>
             </property>
            </widget>
@@ -474,6 +483,25 @@
          </layout>
         </widget>
        </item>
+       <item>
+        <widget class="QgsCollapsibleGroupBox" name="groupBox_2">
+         <property name="title">
+          <string>Variables</string>
+         </property>
+         <layout class="QVBoxLayout" name="verticalLayout_4">
+          <item>
+           <widget class="QgsVariableEditorWidget" name="mVariableEditor" native="true">
+            <property name="minimumSize">
+             <size>
+              <width>0</width>
+              <height>200</height>
+             </size>
+            </property>
+           </widget>
+          </item>
+         </layout>
+        </widget>
+       </item>
        <item>
         <spacer name="verticalSpacer">
          <property name="orientation">
@@ -495,6 +523,18 @@
  </widget>
  <layoutdefault spacing="6" margin="11"/>
  <customwidgets>
+  <customwidget>
+   <class>QgsCollapsibleGroupBox</class>
+   <extends>QGroupBox</extends>
+   <header>qgscollapsiblegroupbox.h</header>
+   <container>1</container>
+  </customwidget>
+  <customwidget>
+   <class>QgsVariableEditorWidget</class>
+   <extends>QWidget</extends>
+   <header location="global">qgsvariableeditorwidget.h</header>
+   <container>1</container>
+  </customwidget>
   <customwidget>
    <class>QgsDataDefinedButton</class>
    <extends>QToolButton</extends>