[composer] Don't use canvas map settings to determine canvas layers

Instead make the layer tree canvas bridge advise on layer set
changes, and tie this into composer. So now composer acts
as a go-between to sync the composer map item's layer set to
the layer tree/canvas layers.

It's not an ideal solution, but avoids the hard link between
compositions and the map canvas.

python/gui/layertree/qgslayertreemapcanvasbridge.sip

@@ -63,6 +63,7 @@ class QgsLayerTreeMapCanvasBridge : QObject
   signals:
     void hasCustomLayerOrderChanged( bool );
     void customLayerOrderChanged( const QStringList& order );
+    void canvasLayersChanged( const QList< QgsMapLayer* >& layers );
 
   protected:
 

src/app/composer/qgscomposer.cpp

@@ -934,6 +934,23 @@ bool QgsComposer::loadFromTemplate( const QDomDocument& templateDoc, bool clearE
   return result;
 }
 
+void QgsComposer::onCanvasLayersChanged( const QList<QgsMapLayer*>& layers )
+{
+  if ( !mComposition )
+    return;
+
+  QList< QgsComposerMap* > maps;
+  mComposition->composerItems( maps );
+
+  Q_FOREACH ( QgsComposerMap* map, maps )
+  {
+    if ( map->keepLayerSet() )
+      continue;
+
+    map->setLayers( layers );
+  }
+}
+
 void QgsComposer::updateStatusCursorPos( QPointF cursorPosition )
 {
   if ( !mComposition )

src/app/composer/qgscomposer.h

@@ -114,6 +114,16 @@ class QgsComposer: public QMainWindow, private Ui::QgsComposerBase
      */
     bool loadFromTemplate( const QDomDocument& templateDoc, bool clearExisting );
 
+  public slots:
+
+    /**
+     * Should be called whenever the app's canvas layers change (or layer order
+     * changes). Required to update composer maps which are synced to the canvas
+     * layer set with the new canvas layer set.
+     * @note added in QGIS 3.0
+     */
+    void onCanvasLayersChanged( const QList< QgsMapLayer* >& layers );
+
   protected:
     //! Move event
     virtual void moveEvent( QMoveEvent * ) override;

src/app/composer/qgscomposermapwidget.cpp

@@ -905,20 +905,20 @@ void QgsComposerMapWidget::on_mKeepLayerListCheckBox_stateChanged( int state )
     return;
   }
 
+  // update map
+  storeCurrentLayerSet();
+  mComposerMap->setKeepLayerSet( state == Qt::Checked );
+
+  // update gui
   if ( state == Qt::Checked )
   {
-    storeCurrentLayerSet();
-    mComposerMap->setKeepLayerSet( true );
-
     // mutually exclusive with following a preset
     mFollowVisibilityPresetCheckBox->setCheckState( Qt::Unchecked );
   }
   else
   {
-    mComposerMap->setLayers( QList<QgsMapLayer*>() );
-    mComposerMap->setKeepLayerSet( false );
-
     mKeepLayerStylesCheckBox->setChecked( Qt::Unchecked );
+    mComposerMap->updateCachedImage();
   }
 
   mKeepLayerStylesCheckBox->setEnabled( state == Qt::Checked );

src/app/qgisapp.cpp

@@ -6773,9 +6773,11 @@ QgsComposer* QgisApp::createNewComposer( QString title )
   mPrintComposersMenu->addAction( newComposerObject->windowAction() );
   newComposerObject->open();
   emit composerAdded( newComposerObject->view() );
-  connect( newComposerObject, SIGNAL( composerAdded( QgsComposerView* ) ), this, SIGNAL( composerAdded( QgsComposerView* ) ) );
-  connect( newComposerObject, SIGNAL( composerWillBeRemoved( QgsComposerView* ) ), this, SIGNAL( composerWillBeRemoved( QgsComposerView* ) ) );
-  connect( newComposerObject, SIGNAL( atlasPreviewFeatureChanged() ), this, SLOT( refreshMapCanvas() ) );
+  connect( newComposerObject, &QgsComposer::composerAdded, this, &QgisApp::composerAdded );
+  connect( newComposerObject, &QgsComposer::composerWillBeRemoved, this, &QgisApp::composerWillBeRemoved );
+  connect( newComposerObject, &QgsComposer::atlasPreviewFeatureChanged, this, &QgisApp::refreshMapCanvas );
+  connect( mLayerTreeCanvasBridge, &QgsLayerTreeMapCanvasBridge::canvasLayersChanged, newComposerObject, &QgsComposer::onCanvasLayersChanged );
+
   markDirty();
   return newComposerObject;
 }
@@ -6875,9 +6877,10 @@ bool QgisApp::loadComposersFromProject( const QDomDocument& doc )
       composerView->updateRulers();
     }
     emit composerAdded( composer->view() );
-    connect( composer, SIGNAL( composerAdded( QgsComposerView* ) ), this, SIGNAL( composerAdded( QgsComposerView* ) ) );
-    connect( composer, SIGNAL( composerWillBeRemoved( QgsComposerView* ) ), this, SIGNAL( composerWillBeRemoved( QgsComposerView* ) ) );
-    connect( composer, SIGNAL( atlasPreviewFeatureChanged() ), this, SLOT( refreshMapCanvas() ) );
+    connect( composer, &QgsComposer::composerAdded, this, &QgisApp::composerAdded );
+    connect( composer, &QgsComposer::composerWillBeRemoved, this, &QgisApp::composerWillBeRemoved );
+    connect( composer, &QgsComposer::atlasPreviewFeatureChanged, this, &QgisApp::refreshMapCanvas );
+    connect( mLayerTreeCanvasBridge, &QgsLayerTreeMapCanvasBridge::canvasLayersChanged, composer, &QgsComposer::onCanvasLayersChanged );
 
     QgsDebugMsg( QString( "Loaded composer %1: %2ms" ).arg( title ).arg( t.elapsed() ) );
   }

src/core/composer/qgscomposermap.cpp

@@ -523,15 +523,11 @@ QList<QgsMapLayer*> QgsComposerMap::layersToRender( const QgsExpressionContext*
     if ( mComposition->project()->mapThemeCollection()->hasMapTheme( presetName ) )
       renderLayers = mComposition->project()->mapThemeCollection()->mapThemeVisibleLayers( presetName );
     else  // fallback to using map canvas layers
-      renderLayers = mComposition->mapSettings().layers();
-  }
-  else if ( mKeepLayerSet )
-  {
-    renderLayers = layers();
+      renderLayers = layers();
   }
   else
   {
-    renderLayers = mComposition->mapSettings().layers();
+    renderLayers = layers();
   }
 
   bool ok = false;

src/core/composer/qgscomposermap.h

@@ -202,14 +202,36 @@ class CORE_EXPORT QgsComposerMap : public QgsComposerItem
     PreviewMode previewMode() const {return mPreviewMode;}
     void setPreviewMode( PreviewMode m );
 
-    //! Getter for flag that determines if the stored layer set should be used or the current layer set of the qgis mapcanvas
+    /**
+     * Getter for flag that determines if a stored layer set should be used
+     * or the current layer set of the QGIS map canvas.
+     * @see setKeepLayerSet()
+     * @see layers()
+     */
     bool keepLayerSet() const {return mKeepLayerSet;}
-    //! Setter for flag that determines if the stored layer set should be used or the current layer set of the qgis mapcanvas
+
+    /**
+     * Setter for flag that determines if the stored layer set should be used
+     * or the current layer set of the QGIS map canvas.
+     * @see keepLayerSet()
+     * @see layers()
+     */
     void setKeepLayerSet( bool enabled ) {mKeepLayerSet = enabled;}
 
-    //! Getter for stored layer set that is used if mKeepLayerSet is true
+    /**
+     * Getter for stored layer set. This will usually be synchronized with the main app canvas
+     * layer set (and layer order), unless the keepLayerSet() flag is true.
+     * @see setLayers()
+     * @see keepLayerSet()
+     */
     QList<QgsMapLayer*> layers() const;
-    //! Setter for stored layer set that is used if mKeepLayerSet is true
+
+    /**
+     * Setter for stored layer set.  This will usually be synchronized with the main app canvas
+     * layer set (and layer order), unless the keepLayerSet() flag is true.
+     * @see layers()
+     * @see keepLayerSet()
+     */
     void setLayers( const QList<QgsMapLayer*> layers );
 
     //! Getter for flag that determines if current styles of layers should be overridden by previously stored styles. @note added in 2.8

src/gui/layertree/qgslayertreemapcanvasbridge.cpp

@@ -34,9 +34,9 @@ QgsLayerTreeMapCanvasBridge::QgsLayerTreeMapCanvasBridge( QgsLayerTreeGroup *roo
     , mAutoEnableCrsTransform( true )
     , mLastLayerCount( !root->findLayers().isEmpty() )
 {
-  connect( root, SIGNAL( addedChildren( QgsLayerTreeNode*, int, int ) ), this, SLOT( nodeAddedChildren( QgsLayerTreeNode*, int, int ) ) );
-  connect( root, SIGNAL( customPropertyChanged( QgsLayerTreeNode*, QString ) ), this, SLOT( nodeCustomPropertyChanged( QgsLayerTreeNode*, QString ) ) );
-  connect( root, SIGNAL( removedChildren( QgsLayerTreeNode*, int, int ) ), this, SLOT( nodeRemovedChildren() ) );
+  connect( root, &QgsLayerTreeGroup::addedChildren, this, &QgsLayerTreeMapCanvasBridge::nodeAddedChildren );
+  connect( root, &QgsLayerTreeGroup::customPropertyChanged, this, &QgsLayerTreeMapCanvasBridge::nodeCustomPropertyChanged );
+  connect( root, &QgsLayerTreeGroup::removedChildren, this, &QgsLayerTreeMapCanvasBridge::nodeRemovedChildren );
   connect( root, &QgsLayerTreeNode::visibilityChanged, this, &QgsLayerTreeMapCanvasBridge::nodeVisibilityChanged );
 
   setCanvasLayers();
@@ -205,6 +205,8 @@ void QgsLayerTreeMapCanvasBridge::setCanvasLayers()
     mFirstCRS = QgsCoordinateReferenceSystem();
 
   mPendingCanvasUpdate = false;
+
+  emit canvasLayersChanged( canvasLayers );
 }
 
 void QgsLayerTreeMapCanvasBridge::readProject( const QDomDocument& doc )

src/gui/layertree/qgslayertreemapcanvasbridge.h

@@ -92,6 +92,13 @@ class GUI_EXPORT QgsLayerTreeMapCanvasBridge : public QObject
     void hasCustomLayerOrderChanged( bool );
     void customLayerOrderChanged( const QStringList& order );
 
+    /**
+     * Emitted when the set of layers (or order of layers) visible in the
+     * canvas changes.
+     * @note added in QGIS 3.0
+     */
+    void canvasLayersChanged( const QList< QgsMapLayer* >& layers );
+
   protected:
 
     void defaultLayerOrder( QgsLayerTreeNode* node, QStringList& order ) const;