Start on reflow support for page collections (needs tests)

python/core/layout/qgslayout.sip

@@ -29,6 +29,16 @@ class QgsLayout : QGraphicsScene, QgsExpressionContextGenerator
     QgsLayout( QgsProject *project );
 %Docstring
  Construct a new layout linked to the specified ``project``.
+
+ If the layout is a "new" layout (as opposed to a layout which will
+ restore a previous state from XML) then initializeDefaults() should be
+ called on the new layout.
+%End
+
+    void initializeDefaults();
+%Docstring
+ Initializes an empty layout, e.g. by adding a default page to the layout. This should be called after creating
+ a new layout.
 %End
 
     QgsProject *project() const;
@@ -191,6 +201,29 @@ class QgsLayout : QGraphicsScene, QgsExpressionContextGenerator
  :rtype: QgsLayoutPageCollection
 %End
 
+    QRectF layoutBounds( bool ignorePages = false, double margin = 0.0 ) const;
+%Docstring
+ Calculates the bounds of all non-gui items in the layout. Ignores snap lines, mouse handles
+ and other cosmetic items.
+ \param ignorePages set to true to ignore page items
+ \param margin optional marginal (in percent, e.g., 0.05 = 5% ) to add around items
+ :return: layout bounds, in layout units.
+ :rtype: QRectF
+%End
+
+    void addLayoutItem( QgsLayoutItem *item /Transfer/ );
+%Docstring
+ Adds an ``item`` to the layout. This should be called instead of the base class addItem()
+ method. Ownership of the item is transferred to the layout.
+%End
+
+  public slots:
+
+    void updateBounds();
+%Docstring
+ Updates the scene bounds of the layout.
+%End
+
   signals:
 
     void variablesChanged();

python/core/layout/qgslayoutpagecollection.sip

@@ -65,6 +65,9 @@ class QgsLayoutPageCollection : QObject
  to the collection, and the page will automatically be added to the collection's
  layout() (there is no need to manually add the page item to the layout).
  The page will be added after all pages currently contained in the collection.
+
+ Calling addPage() automatically triggers a reflow() of pages.
+
 .. seealso:: insertPage()
 %End
 
@@ -80,6 +83,8 @@ class QgsLayoutPageCollection : QObject
  (Page numbers in collections begin at 0 - so a ``beforePage`` of 0 will insert
  the page before all existing pages).
 
+ Calling insertPage() automatically triggers a reflow() of pages.
+
 .. seealso:: addPage()
 %End
 
@@ -90,6 +95,8 @@ class QgsLayoutPageCollection : QObject
 
  Page numbers in collections begin at 0 - so a ``pageNumber`` of 0 will delete
  the first page in the collection.
+
+ Calling deletePage() automatically triggers a reflow() of pages.
 %End
 
     void setPageStyleSymbol( QgsFillSymbol *symbol );
@@ -107,6 +114,19 @@ class QgsLayoutPageCollection : QObject
  :rtype: QgsFillSymbol
 %End
 
+    void reflow();
+%Docstring
+ Forces the page collection to reflow the arrangement of pages, e.g. to account
+ for page size/orientation change.
+%End
+
+    double maximumPageWidth() const;
+%Docstring
+ Returns the maximum width of pages in the collection. The returned value is
+ in layout units.
+ :rtype: float
+%End
+
 };
 
 /************************************************************************

src/core/layout/qgslayout.cpp

@@ -25,6 +25,14 @@ QgsLayout::QgsLayout( QgsProject *project )
   setBackgroundBrush( QColor( 215, 215, 215 ) );
 }
 
+void QgsLayout::initializeDefaults()
+{
+  // default to a A4 landscape page
+  QgsLayoutItemPage *page = new QgsLayoutItemPage( this );
+  page->setPageSize( QgsLayoutSize( 297, 210, QgsUnitTypes::LayoutMillimeters ) );
+  mPageCollection->addPage( page );
+}
+
 QgsProject *QgsLayout::project() const
 {
   return mProject;
@@ -112,3 +120,48 @@ QgsLayoutPageCollection *QgsLayout::pageCollection()
 {
   return mPageCollection.get();
 }
+
+QRectF QgsLayout::layoutBounds( bool ignorePages, double margin ) const
+{
+  //start with an empty rectangle
+  QRectF bounds;
+
+  //add all QgsComposerItems and QgsPaperItems which are in the composition
+  Q_FOREACH ( const QGraphicsItem *item, items() )
+  {
+    const QgsLayoutItem *layoutItem = dynamic_cast<const QgsLayoutItem *>( item );
+    if ( !layoutItem )
+      continue;
+
+    bool isPage = layoutItem->type() == QgsLayoutItemRegistry::LayoutPage;
+    if ( !isPage || !ignorePages )
+    {
+      //expand bounds with current item's bounds
+      if ( bounds.isValid() )
+        bounds = bounds.united( item->sceneBoundingRect() );
+      else
+        bounds = item->sceneBoundingRect();
+    }
+  }
+
+  if ( bounds.isValid() && margin > 0.0 )
+  {
+    //finally, expand bounds out by specified margin of page size
+    double maxWidth = mPageCollection->maximumPageWidth();
+    bounds.adjust( -maxWidth * margin, -maxWidth * margin, maxWidth * margin, maxWidth * margin );
+  }
+
+  return bounds;
+
+}
+
+void QgsLayout::addLayoutItem( QgsLayoutItem *item )
+{
+  addItem( item );
+  updateBounds();
+}
+
+void QgsLayout::updateBounds()
+{
+  setSceneRect( layoutBounds( false, 0.05 ) );
+}

src/core/layout/qgslayout.h

@@ -45,9 +45,19 @@ class CORE_EXPORT QgsLayout : public QGraphicsScene, public QgsExpressionContext
 
     /**
      * Construct a new layout linked to the specified \a project.
+     *
+     * If the layout is a "new" layout (as opposed to a layout which will
+     * restore a previous state from XML) then initializeDefaults() should be
+     * called on the new layout.
      */
     QgsLayout( QgsProject *project );
 
+    /**
+     * Initializes an empty layout, e.g. by adding a default page to the layout. This should be called after creating
+     * a new layout.
+     */
+    void initializeDefaults();
+
     /**
      * The project associated with the layout. Used to get access to layers, map themes,
      * relations and various other bits. It is never null.
@@ -211,6 +221,28 @@ class CORE_EXPORT QgsLayout : public QGraphicsScene, public QgsExpressionContext
      */
     QgsLayoutPageCollection *pageCollection();
 
+    /**
+     * Calculates the bounds of all non-gui items in the layout. Ignores snap lines, mouse handles
+     * and other cosmetic items.
+     * \param ignorePages set to true to ignore page items
+     * \param margin optional marginal (in percent, e.g., 0.05 = 5% ) to add around items
+     * \returns layout bounds, in layout units.
+     */
+    QRectF layoutBounds( bool ignorePages = false, double margin = 0.0 ) const;
+
+    /**
+     * Adds an \a item to the layout. This should be called instead of the base class addItem()
+     * method. Ownership of the item is transferred to the layout.
+     */
+    void addLayoutItem( QgsLayoutItem *item SIP_TRANSFER );
+
+  public slots:
+
+    /**
+     * Updates the scene bounds of the layout.
+     */
+    void updateBounds();
+
   signals:
 
     /**

src/core/layout/qgslayoutpagecollection.cpp

@@ -17,6 +17,8 @@
 #include "qgslayoutpagecollection.h"
 #include "qgslayout.h"
 
+#define SPACE_BETWEEN_PAGES 10
+
 QgsLayoutPageCollection::QgsLayoutPageCollection( QgsLayout *layout )
   : QObject( layout )
   , mLayout( layout )
@@ -41,6 +43,29 @@ void QgsLayoutPageCollection::setPageStyleSymbol( QgsFillSymbol *symbol )
   mPageStyleSymbol.reset( static_cast<QgsFillSymbol *>( symbol->clone() ) );
 }
 
+void QgsLayoutPageCollection::reflow()
+{
+  double currentY = 0;
+  QgsLayoutPoint p( 0, 0, mLayout->units() );
+  Q_FOREACH ( QgsLayoutItemPage *page, mPages )
+  {
+    page->attemptMove( p );
+    currentY += mLayout->convertToLayoutUnits( page->pageSize() ).height() + SPACE_BETWEEN_PAGES;
+    p.setY( currentY );
+  }
+  mLayout->updateBounds();
+}
+
+double QgsLayoutPageCollection::maximumPageWidth() const
+{
+  double maxWidth = 0;
+  Q_FOREACH ( QgsLayoutItemPage *page, mPages )
+  {
+    maxWidth = qMax( maxWidth, mLayout->convertToLayoutUnits( page->pageSize() ).width() );
+  }
+  return maxWidth;
+}
+
 QgsLayout *QgsLayoutPageCollection::layout() const
 {
   return mLayout;
@@ -65,6 +90,7 @@ void QgsLayoutPageCollection::addPage( QgsLayoutItemPage *page )
 {
   mPages.append( page );
   mLayout->addItem( page );
+  reflow();
 }
 
 void QgsLayoutPageCollection::insertPage( QgsLayoutItemPage *page, int beforePage )
@@ -81,6 +107,7 @@ void QgsLayoutPageCollection::insertPage( QgsLayoutItemPage *page, int beforePag
     mPages.insert( beforePage, page );
   }
   mLayout->addItem( page );
+  reflow();
 }
 
 void QgsLayoutPageCollection::deletePage( int pageNumber )
@@ -91,6 +118,7 @@ void QgsLayoutPageCollection::deletePage( int pageNumber )
   QgsLayoutItemPage *page = mPages.takeAt( pageNumber );
   mLayout->removeItem( page );
   page->deleteLater();
+  reflow();
 }
 
 void QgsLayoutPageCollection::createDefaultPageStyleSymbol()

src/core/layout/qgslayoutpagecollection.h

@@ -78,6 +78,9 @@ class CORE_EXPORT QgsLayoutPageCollection : public QObject
      * to the collection, and the page will automatically be added to the collection's
      * layout() (there is no need to manually add the page item to the layout).
      * The page will be added after all pages currently contained in the collection.
+     *
+     * Calling addPage() automatically triggers a reflow() of pages.
+     *
      * \see insertPage()
      */
     void addPage( QgsLayoutItemPage *page SIP_TRANSFER );
@@ -93,6 +96,8 @@ class CORE_EXPORT QgsLayoutPageCollection : public QObject
      * (Page numbers in collections begin at 0 - so a \a beforePage of 0 will insert
      * the page before all existing pages).
      *
+     * Calling insertPage() automatically triggers a reflow() of pages.
+     *
      * \see addPage()
      */
     void insertPage( QgsLayoutItemPage *page SIP_TRANSFER, int beforePage );
@@ -103,6 +108,8 @@ class CORE_EXPORT QgsLayoutPageCollection : public QObject
      *
      * Page numbers in collections begin at 0 - so a \a pageNumber of 0 will delete
      * the first page in the collection.
+     *
+     * Calling deletePage() automatically triggers a reflow() of pages.
      */
     void deletePage( int pageNumber );
 
@@ -120,6 +127,18 @@ class CORE_EXPORT QgsLayoutPageCollection : public QObject
      */
     const QgsFillSymbol *pageStyleSymbol() const { return mPageStyleSymbol.get(); }
 
+    /**
+     * Forces the page collection to reflow the arrangement of pages, e.g. to account
+     * for page size/orientation change.
+     */
+    void reflow();
+
+    /**
+     * Returns the maximum width of pages in the collection. The returned value is
+     * in layout units.
+     */
+    double maximumPageWidth() const;
+
   private:
 
     QgsLayout *mLayout = nullptr;

src/gui/layout/qgslayoutviewtooladditem.cpp

@@ -115,7 +115,7 @@ void QgsLayoutViewToolAddItem::layoutReleaseEvent( QgsLayoutViewMouseEvent *even
   settings.setValue( QStringLiteral( "LayoutDesigner/lastItemHeight" ), item->sizeWithUnits().height() );
   settings.setValue( QStringLiteral( "LayoutDesigner/lastSizeUnit" ), static_cast< int >( item->sizeWithUnits().units() ) );
 
-  layout()->addItem( item );
+  layout()->addLayoutItem( item );
 }
 
 void QgsLayoutViewToolAddItem::deactivate()