Add support for contextual WMS legend graphics (hub #11859)

Developed with funding from Regione Toscana SITA (CIG: Z410C90D94)

src/app/qgisapp.cpp

@@ -393,7 +393,9 @@ void QgisApp::layerTreeViewDoubleClicked( const QModelIndex& index )
       QgsRasterLayer* rlayer = qobject_cast<QgsRasterLayer*>( layer );
       if ( rlayer && rlayer->providerType() == "wms" )
       {
-        QImage img = rlayer->dataProvider()->getLegendGraphic( mMapCanvas->scale() );
+        const QgsMapCanvas* canvas = mapCanvas();
+        QgsRectangle visibleExtent = canvas->mapSettings().outputExtentToLayerExtent( rlayer, canvas->extent() ); // in layer projection
+        QImage img = rlayer->dataProvider()->getLegendGraphic( mMapCanvas->scale(), false, &visibleExtent );
 
         QFrame* popup = new QFrame();
         popup->setAttribute( Qt::WA_DeleteOnClose );

src/core/layertree/qgslayertreemodel.h

@@ -149,7 +149,7 @@ class CORE_EXPORT QgsLayerTreeModel : public QAbstractItemModel
 
     //! Force only display of legend nodes which are valid for given map settings.
     //! Setting null pointer or invalid map settings will disable the functionality.
-    //! Ownership of map settings pointer does not change.
+    //! Ownership of map settings pointer does not change, a copy is made.
     //! @note added in 2.6
     void setLegendFilterByMap( const QgsMapSettings* settings );
     const QgsMapSettings* legendFilterByMap() const { return mLegendFilterByMapSettings.data(); }

src/core/layertree/qgslayertreemodellegendnode.cpp

@@ -4,6 +4,9 @@
   Date                 : August 2014
   Copyright            : (C) 2014 by Martin Dobias
   Email                : wonder dot sk at gmail dot com
+
+  QgsWMSLegendNode     : Sandro Santilli < strk at keybit dot net >
+
  ***************************************************************************
  *                                                                         *
  *   This program is free software; you can redistribute it and/or modify  *
@@ -478,3 +481,139 @@ QSizeF QgsRasterSymbolLegendNode::drawSymbol( const QgsLegendSettings& settings,
   }
   return settings.symbolSize();
 }
+
+// -------------------------------------------------------------------------
+
+QgsWMSLegendNode::QgsWMSLegendNode( QgsLayerTreeLayer* nodeLayer, QObject* parent )
+    : QgsLayerTreeModelLegendNode( nodeLayer, parent )
+    , mValid( false )
+{
+}
+
+const QImage& QgsWMSLegendNode::getLegendGraphic() const
+{
+  if ( ! mValid && ! mFetcher )
+  {
+    // or maybe in presence of a downloader we should just delete it
+    // and start a new one ?
+
+    QgsRasterLayer* layer = qobject_cast<QgsRasterLayer*>( mLayerNode->layer() );
+    const QgsLayerTreeModel* mod = model();
+    if ( ! mod ) return mImage;
+    const QgsMapSettings* ms = mod->legendFilterByMap();
+
+    QgsRasterDataProvider* prov = layer->dataProvider();
+
+    Q_ASSERT( ! mFetcher );
+    mFetcher.reset( prov->getLegendGraphicFetcher( ms ) );
+    if ( mFetcher )
+    {
+      connect( mFetcher.data(), SIGNAL( finish( const QImage& ) ), this, SLOT( getLegendGraphicFinished( const QImage& ) ) );
+      connect( mFetcher.data(), SIGNAL( error( const QString& ) ), this, SLOT( getLegendGraphicErrored( const QString& ) ) );
+      connect( mFetcher.data(), SIGNAL( progress( qint64, qint64 ) ), this, SLOT( getLegendGraphicProgress( qint64, qint64 ) ) );
+      mFetcher->start();
+    } // else QgsDebugMsg("XXX No legend supported ?");
+
+  }
+
+  return mImage;
+}
+
+QVariant QgsWMSLegendNode::data( int role ) const
+{
+  //QgsDebugMsg( QString("XXX data called with role %1 -- mImage size is %2x%3").arg(role).arg(mImage.width()).arg(mImage.height()) );
+
+  if ( role == Qt::DecorationRole )
+  {
+    return QPixmap::fromImage( getLegendGraphic() );
+  }
+  else if ( role == Qt::SizeHintRole )
+  {
+    return getLegendGraphic().size();
+  }
+  return QVariant();
+}
+
+QSizeF QgsWMSLegendNode::drawSymbol( const QgsLegendSettings& settings, ItemContext* ctx, double itemHeight ) const
+{
+  Q_UNUSED( itemHeight );
+
+  if ( ctx )
+  {
+    ctx->painter->drawImage( QRectF( ctx->point, settings.wmsLegendSize() ),
+                             mImage,
+                             QRectF( QPointF( 0, 0 ), mImage.size() ) );
+  }
+  return settings.wmsLegendSize();
+}
+
+/* private */
+QImage QgsWMSLegendNode::renderMessage( const QString& msg ) const
+{
+  const int fontHeight = 10;
+  const int margin = fontHeight / 2;
+  const int nlines = 1;
+
+  const int w = 512, h = fontHeight * nlines + margin * ( nlines + 1 );
+  QImage theImage( w, h, QImage::Format_ARGB32_Premultiplied );
+  QPainter painter;
+  painter.begin( &theImage );
+  painter.setPen( QColor( 255, 0, 0 ) );
+  painter.setFont( QFont( "Chicago", fontHeight ) );
+  painter.fillRect( 0, 0, w, h, QColor( 255, 255, 255 ) );
+  painter.drawText( 0, margin + fontHeight, msg );
+  //painter.drawText(0,2*(margin+fontHeight),QString("retrying in 5 seconds..."));
+  painter.end();
+
+  return theImage;
+}
+
+void QgsWMSLegendNode::getLegendGraphicProgress( qint64 cur, qint64 tot )
+{
+  QString msg = QString( "Downloading... %1/%2" ).arg( cur ).arg( tot );
+  //QgsDebugMsg ( QString("XXX %1").arg(msg) );
+  mImage = renderMessage( msg );
+  emit dataChanged();
+}
+
+void QgsWMSLegendNode::getLegendGraphicErrored( const QString& msg )
+{
+  if ( ! mFetcher ) return; // must be coming after finish
+
+  mImage = renderMessage( msg );
+  //QgsDebugMsg( QString("XXX emitting dataChanged after writing an image of %1x%2").arg(mImage.width()).arg(mImage.height()) );
+
+  emit dataChanged();
+
+  mFetcher.reset();
+
+  mValid = true; // we consider it valid anyway
+  // ... but remove validity after 5 seconds
+  //QTimer::singleShot(5000, this, SLOT(invalidateMapBasedData()));
+}
+
+void QgsWMSLegendNode::getLegendGraphicFinished( const QImage& theImage )
+{
+  if ( ! mFetcher ) return; // must be coming after error
+
+  //QgsDebugMsg( QString("XXX legend graphic finished, image is %1x%2").arg(theImage.width()).arg(theImage.height()) );
+  if ( ! theImage.isNull() )
+  {
+    if ( theImage != mImage )
+    {
+      mImage = theImage;
+      //QgsDebugMsg( QString("XXX emitting dataChanged") );
+      emit dataChanged();
+    }
+    mValid = true; // only if not null I guess
+  }
+  mFetcher.reset();
+}
+
+void QgsWMSLegendNode::invalidateMapBasedData()
+{
+  //QgsDebugMsg( QString("XXX invalidateMapBasedData called") );
+  // TODO: do this only if this extent != prev extent ?
+  mValid = false;
+  emit dataChanged();
+}

src/core/layertree/qgslayertreemodellegendnode.h

@@ -4,6 +4,9 @@
   Date                 : August 2014
   Copyright            : (C) 2014 by Martin Dobias
   Email                : wonder dot sk at gmail dot com
+
+  QgsWMSLegendNode     : Sandro Santilli < strk at keybit dot net >
+
  ***************************************************************************
  *                                                                         *
  *   This program is free software; you can redistribute it and/or modify  *
@@ -19,9 +22,12 @@
 #include <QIcon>
 #include <QObject>
 
+#include "qgsrasterdataprovider.h" // for QgsImageFetcher dtor visibility
+
 class QgsLayerTreeLayer;
 class QgsLayerTreeModel;
 class QgsLegendSettings;
+class QgsMapSettings;
 class QgsSymbolV2;
 
 /**
@@ -222,4 +228,44 @@ class CORE_EXPORT QgsRasterSymbolLegendNode : public QgsLayerTreeModelLegendNode
     QString mLabel;
 };
 
+class QgsImageFetcher;
+
+/**
+ * Implementation of legend node interface for displaying WMS legend entries
+ *
+ * @note added in 2.8
+ */
+class CORE_EXPORT QgsWMSLegendNode : public QgsLayerTreeModelLegendNode
+{
+    Q_OBJECT
+
+  public:
+    QgsWMSLegendNode( QgsLayerTreeLayer* nodeLayer, QObject* parent = 0 );
+
+    virtual QVariant data( int role ) const;
+
+    virtual QSizeF drawSymbol( const QgsLegendSettings& settings, ItemContext* ctx, double itemHeight ) const;
+
+    virtual void invalidateMapBasedData();
+
+  private slots:
+
+    void getLegendGraphicFinished( const QImage& );
+    void getLegendGraphicErrored( const QString& );
+    void getLegendGraphicProgress( qint64, qint64 );
+
+  private:
+
+    // Lazily initializes mImage
+    const QImage& getLegendGraphic() const;
+
+    QImage renderMessage( const QString& msg ) const;
+
+    QImage mImage;
+
+    bool mValid;
+
+    mutable QScopedPointer<QgsImageFetcher> mFetcher;
+};
+
 #endif // QGSLAYERTREEMODELLEGENDNODE_H

src/core/qgsmaplayerlegend.cpp

@@ -227,12 +227,7 @@ QList<QgsLayerTreeModelLegendNode*> QgsDefaultRasterLayerLegend::createLayerTree
   // temporary solution for WMS. Ideally should be done with a delegate.
   if ( mLayer->providerType() == "wms" )
   {
-    QImage legendGraphic = mLayer->dataProvider()->getLegendGraphic();
-    if ( !legendGraphic.isNull() )
-    {
-      QgsDebugMsg( QString( "downloaded legend with dimension width:" ) + QString::number( legendGraphic.width() ) + QString( " and Height:" ) + QString::number( legendGraphic.height() ) );
-      nodes << new QgsImageLegendNode( nodeLayer, legendGraphic );
-    }
+    nodes << new QgsWMSLegendNode( nodeLayer );
   }
 
   QgsLegendColorList rasterItemList = mLayer->legendSymbologyItems();

src/core/raster/qgsrasterdataprovider.h

@@ -4,6 +4,9 @@
     Date                 : Mar 11, 2005
     Copyright            : (C) 2005 by Brendan Morley
     email                : morb at ozemail dot com dot au
+
+    async legend fetcher : Sandro Santilli < strk at keybit dot net >
+
  ***************************************************************************/
 
 /***************************************************************************
@@ -46,6 +49,31 @@ class QByteArray;
 
 class QgsPoint;
 class QgsRasterIdentifyResult;
+class QgsMapSettings;
+
+/**
+ * \class Handles asynchronous download of images
+ *
+ * \note added in 2.8
+ */
+class QgsImageFetcher : public QObject
+{
+    Q_OBJECT
+  public:
+
+    QgsImageFetcher() {};
+    virtual ~QgsImageFetcher( ) {}
+
+    // Make sure to connect to "finish" and "error" before starting
+    virtual void start() = 0;
+
+  signals:
+
+    void finish( const QImage& legend );
+    void progress( qint64 received, qint64 total );
+    void error( const QString& msg );
+};
+
 
 /** \ingroup core
  * Base class for raster data providers.
@@ -201,14 +229,39 @@ class CORE_EXPORT QgsRasterDataProvider : public QgsDataProvider, public QgsRast
     }
 
     /** \brief Returns the legend rendered as pixmap
-     *  useful for that layer that need to get legend layer remotly as WMS */
-    virtual QImage getLegendGraphic( double scale = 0, bool forceRefresh = false )
+     *
+     *  useful for that layer that need to get legend layer remotely as WMS
+     * \param visibleExtent Visible extent for providers supporting
+     *                      contextual legends, in layer CRS
+     * \note visibleExtent parameter added in 2.8
+     */
+    virtual QImage getLegendGraphic( double scale = 0, bool forceRefresh = false, const QgsRectangle * visibleExtent = 0 )
     {
       Q_UNUSED( scale );
       Q_UNUSED( forceRefresh );
+      Q_UNUSED( visibleExtent );
       return QImage();
     }
 
+    /**
+     * \class Get an image downloader for the raster legend
+     *
+     * \param mapSettings map settings for legend providers supporting
+     *                    contextual legends.
+     *
+     * \return a download handler or null if the provider does not support
+     *         legend at all. Ownership of the returned object is transferred
+     *         to caller.
+     *
+     * \note added in 2.8
+     *
+     */
+    virtual QgsImageFetcher* getLegendGraphicFetcher( const QgsMapSettings* mapSettings )
+    {
+      Q_UNUSED( mapSettings );
+      return 0;
+    }
+
     /** \brief Create pyramid overviews */
     virtual QString buildPyramids( const QList<QgsRasterPyramid> & thePyramidList,
                                    const QString & theResamplingMethod = "NEAREST",

src/providers/wms/qgswmscapabilities.cpp

@@ -93,6 +93,9 @@ bool QgsWmsSettings::parseUri( QString uriString )
 
   mCrsId = uri.param( "crs" );
 
+  mEnableContextualLegend = uri.param( "contextualWMSLegend" ).toInt();
+  QgsDebugMsg( QString( "Contextual legend: %1" ).arg( mEnableContextualLegend ) );
+
   mFeatureCount = uri.param( "featureCount" ).toInt(); // default to 0
 
   return true;

src/providers/wms/qgswmscapabilities.h

@@ -524,6 +524,8 @@ class QgsWmsSettings
 
     QString mCrsId;
 
+    bool mEnableContextualLegend;
+
     friend class QgsWmsProvider;
 };