Fix drawing of rulers with multipage layouts

python/core/layout/qgslayoutpagecollection.sip

@@ -137,6 +137,13 @@ Size of page shadow, in layout coordinates
  :rtype: float
 %End
 
+  signals:
+
+    void changed();
+%Docstring
+ Emitted when pages are added or removed from the collection.
+%End
+
 };
 
 /************************************************************************

python/gui/layout/qgslayoutview.sip

@@ -186,6 +186,8 @@ class QgsLayoutView: QGraphicsView
 
     virtual void resizeEvent( QResizeEvent *event );
 
+    virtual void scrollContentsBy( int dx, int dy );
+
 
 };
 

src/app/layout/qgslayoutdesignerdialog.cpp

@@ -257,15 +257,10 @@ void QgsLayoutDesignerDialog::open()
 {
   show();
   activate();
-  mView->zoomFull(); // zoomFull() does not work properly until we have called show()
-
-#if 0 // TODO
-
   if ( mView )
   {
-    mView->updateRulers();
+    mView->zoomFull(); // zoomFull() does not work properly until we have called show()
   }
-#endif
 }
 
 void QgsLayoutDesignerDialog::activate()

src/core/layout/qgslayoutpagecollection.cpp

@@ -52,6 +52,7 @@ void QgsLayoutPageCollection::reflow()
     p.setY( currentY );
   }
   mLayout->updateBounds();
+  emit changed();
 }
 
 double QgsLayoutPageCollection::maximumPageWidth() const

src/core/layout/qgslayoutpagecollection.h

@@ -145,6 +145,13 @@ class CORE_EXPORT QgsLayoutPageCollection : public QObject
      */
     double maximumPageWidth() const;
 
+  signals:
+
+    /**
+     * Emitted when pages are added or removed from the collection.
+     */
+    void changed();
+
   private:
 
     QgsLayout *mLayout = nullptr;

src/gui/layout/qgslayoutruler.cpp

@@ -66,9 +66,8 @@ void QgsLayoutRuler::paintEvent( QPaintEvent *event )
   {
     return;
   }
-#if 0
+
   QgsLayout *layout = mView->currentLayout();
-#endif
   QPainter p( this );
 
   QTransform t = mTransform.inverted();
@@ -137,14 +136,23 @@ void QgsLayoutRuler::paintEvent( QPaintEvent *event )
       double startY = t.map( QPointF( 0, 0 ) ).y(); //start position in mm (total including space between pages)
       double endY = t.map( QPointF( 0, height() ) ).y(); //stop position in mm (total including space between pages)
 
-#if 0 // TODO
-      int startPage = ( int )( startY / ( layout->paperHeight() + layout->spaceBetweenPages() ) );
-#endif
-
+      // work out start page
       int startPage = 0;
-      if ( startPage < 0 )
+      int endPage = 0;
+      double currentY = 0;
+      double currentPageY = 0;
+      for ( int page = 0; page < layout->pageCollection()->pageCount(); ++page )
       {
-        startPage = 0;
+        if ( currentY < startY )
+        {
+          startPage = page;
+          currentPageY = currentY;
+        }
+        endPage = page;
+
+        currentY += layout->pageCollection()->page( startPage )->rect().height() + layout->pageCollection()->SPACE_BETWEEN_PAGES;
+        if ( currentY > endY )
+          break;
       }
 
       if ( startY < 0 )
@@ -177,15 +185,6 @@ void QgsLayoutRuler::paintEvent( QPaintEvent *event )
         drawSmallDivisions( &p, beforePageCoord + mmDisplay, numSmallDivisions, -mmDisplay, startY );
       }
 
-#if 0 //TODO
-      int endPage = ( int )( endY / ( layout->paperHeight() + layout->spaceBetweenPages() ) );
-      if ( endPage > ( mLayout->numPages() - 1 ) )
-      {
-        endPage = mLayout->numPages() - 1;
-      }
-#endif
-      int endPage = 0;
-
       double nextPageStartPos = 0;
       int nextPageStartPixel = 0;
 
@@ -193,14 +192,14 @@ void QgsLayoutRuler::paintEvent( QPaintEvent *event )
       {
         double pageCoord = 0; //page coordinate in mm
         //total (composition) coordinate in mm, including space between pages
-#if 0 //TODO
-        double totalCoord = i * ( layout->paperHeight() + layout->spaceBetweenPages() );
+
+        double totalCoord = currentPageY;
 
         //position of next page
         if ( i < endPage )
         {
           //not the last page
-          nextPageStartPos = ( i + 1 ) * ( layout->paperHeight() + layout->spaceBetweenPages() );
+          nextPageStartPos = currentPageY + layout->pageCollection()->page( i )->rect().height() + layout->pageCollection()->SPACE_BETWEEN_PAGES;
           nextPageStartPixel = mTransform.map( QPointF( 0, nextPageStartPos ) ).y();
         }
         else
@@ -209,8 +208,7 @@ void QgsLayoutRuler::paintEvent( QPaintEvent *event )
           nextPageStartPos = 0;
           nextPageStartPixel = 0;
         }
-#endif
-        double totalCoord = 0;
+
         while ( ( totalCoord < nextPageStartPos ) || ( ( nextPageStartPos == 0 ) && ( totalCoord <= endY ) ) )
         {
           double pixelCoord = mTransform.map( QPointF( 0, totalCoord ) ).y();
@@ -232,6 +230,7 @@ void QgsLayoutRuler::paintEvent( QPaintEvent *event )
           pageCoord += mmDisplay;
           totalCoord += mmDisplay;
         }
+        currentPageY += layout->pageCollection()->page( i )->rect().height() + layout->pageCollection()->SPACE_BETWEEN_PAGES;
       }
       break;
     }
@@ -407,10 +406,6 @@ int QgsLayoutRuler::optimumNumberDivisions( double rulerScale, int scaleMultiple
 
 void QgsLayoutRuler::setSceneTransform( const QTransform &transform )
 {
-#if 0
-  QString debug = QString::number( transform.dx() ) + ',' + QString::number( transform.dy() ) + ','
-                  + QString::number( transform.m11() ) + ',' + QString::number( transform.m22() );
-#endif
   mTransform = transform;
   update();
 }

src/gui/layout/qgslayoutview.cpp

@@ -53,6 +53,9 @@ void QgsLayoutView::setCurrentLayout( QgsLayout *layout )
 {
   setScene( layout );
 
+  connect( layout->pageCollection(), &QgsLayoutPageCollection::changed, this, &QgsLayoutView::updateRulers );
+  updateRulers();
+
   //emit layoutSet, so that designer dialogs can update for the new layout
   emit layoutSet( layout );
 }
@@ -131,6 +134,7 @@ void QgsLayoutView::setVerticalRuler( QgsLayoutRuler *ruler )
 void QgsLayoutView::zoomFull()
 {
   fitInView( scene()->sceneRect(), Qt::KeepAspectRatio );
+  updateRulers();
   emit zoomLevelChanged();
 }
 
@@ -305,6 +309,12 @@ void QgsLayoutView::resizeEvent( QResizeEvent *event )
   emit zoomLevelChanged();
 }
 
+void QgsLayoutView::scrollContentsBy( int dx, int dy )
+{
+  QGraphicsView::scrollContentsBy( dx, dy );
+  updateRulers();
+}
+
 void QgsLayoutView::updateRulers()
 {
   if ( mHorizontalRuler )

src/gui/layout/qgslayoutview.h

@@ -209,6 +209,7 @@ class GUI_EXPORT QgsLayoutView: public QGraphicsView
     void keyPressEvent( QKeyEvent *event ) override;
     void keyReleaseEvent( QKeyEvent *event ) override;
     void resizeEvent( QResizeEvent *event ) override;
+    void scrollContentsBy( int dx, int dy ) override;
 
   private slots: