[FEATURE] Add a dock widget showing snap guides for current page

Allows creation of snap lines at specific locations, and
adjusting position of existing guides to exact coordinates

python/core/layout/qgslayoutguidecollection.sip

@@ -145,6 +145,7 @@ class QgsLayoutGuideCollection : QAbstractListModel
       PositionRole,
       UnitsRole,
       PageRole,
+      LayoutPositionRole,
     };
 
     QgsLayoutGuideCollection( QgsLayout *layout );
@@ -203,6 +204,11 @@ class QgsLayoutGuideProxyModel : QSortFilterProxyModel
  Page numbers begin at 0.
 %End
 
+    void setPage( int page );
+%Docstring
+ Sets the current ``page`` for filtering matching guides. Page numbers begin at 0.
+%End
+
     virtual bool filterAcceptsRow( int sourceRow, const QModelIndex &sourceParent ) const;
 
     virtual bool lessThan( const QModelIndex &left, const QModelIndex &right ) const;

python/core/layout/qgslayoutsnapper.sip

@@ -78,6 +78,20 @@ class QgsLayoutSnapper
  :rtype: QPointF
 %End
 
+    double snapPointToGuides( double original, QgsLayoutGuide::Orientation orientation, double scaleFactor, bool &snapped /Out/ ) const;
+%Docstring
+ Snaps a layout coordinate ``point`` to the grid. If ``point``
+ was snapped, ``snapped`` will be set to true.
+
+ The ``scaleFactor`` argument should be set to the transformation from
+ scalar transform from layout coordinates to pixels, i.e. the
+ graphics view transform().m11() value.
+
+ If snapToGrid() is disabled, this method will return the point
+ unchanged.
+ :rtype: float
+%End
+
 };
 
 /************************************************************************

python/gui/layout/qgslayoutview.sip

@@ -103,6 +103,15 @@ class QgsLayoutView: QGraphicsView
  :rtype: QgsLayoutViewMenuProvider
 %End
 
+    int currentPage() const;
+%Docstring
+ Returns the page visible in the view. This method
+ considers the page at the center of the view as the current visible
+ page.
+.. seealso:: pageChanged()
+ :rtype: int
+%End
+
   public slots:
 
     void zoomFull();
@@ -147,9 +156,9 @@ class QgsLayoutView: QGraphicsView
 
     void emitZoomLevelChanged();
 
-    void updateRulers();
+    void viewChanged();
 %Docstring
- Updates associated rulers after view extent or zoom has changed.
+ Updates associated rulers and other widgets after view extent or zoom has changed.
  This should be called after calling any of the QGraphicsView
  base class methods which alter the view's zoom level or extent,
  i.e. QGraphicsView.fitInView().
@@ -182,6 +191,14 @@ class QgsLayoutView: QGraphicsView
  the layout coordinate system.
 %End
 
+    void pageChanged( int page );
+%Docstring
+ Emitted when the page visible in the view is changed. This signal
+ considers the page at the center of the view as the current visible
+ page.
+.. seealso:: currentPage()
+%End
+
   protected:
     virtual void mousePressEvent( QMouseEvent *event );
 

src/app/CMakeLists.txt

@@ -157,6 +157,7 @@ SET(QGIS_APP_SRCS
 
   layout/qgslayoutaddpagesdialog.cpp
   layout/qgslayoutdesignerdialog.cpp
+  layout/qgslayoutguidewidget.cpp
   layout/qgslayoutappmenuprovider.cpp
   layout/qgslayoutpagepropertieswidget.cpp
   layout/qgslayoutpropertieswidget.cpp
@@ -339,6 +340,7 @@ SET (QGIS_APP_MOC_HDRS
   layout/qgslayoutaddpagesdialog.h
   layout/qgslayoutappmenuprovider.h
   layout/qgslayoutdesignerdialog.h
+  layout/qgslayoutguidewidget.h
   layout/qgslayoutpagepropertieswidget.h
   layout/qgslayoutpropertieswidget.h
 

src/app/layout/qgslayoutdesignerdialog.cpp

@@ -37,6 +37,7 @@
 #include "qgspanelwidget.h"
 #include "qgsdockwidget.h"
 #include "qgslayoutpagepropertieswidget.h"
+#include "qgslayoutguidewidget.h"
 #include <QShortcut>
 #include <QComboBox>
 #include <QLineEdit>
@@ -257,8 +258,20 @@ QgsLayoutDesignerDialog::QgsLayoutDesignerDialog( QWidget *parent, Qt::WindowFla
   mItemDock->setWidget( mItemPropertiesStack );
   mPanelsMenu->addAction( mItemDock->toggleViewAction() );
 
+  mGuideDock = new QgsDockWidget( tr( "Guides" ), this );
+  mGuideDock->setObjectName( QStringLiteral( "GuideDock" ) );
+  mGuideDock->setMinimumWidth( minDockWidth );
+  mGuideStack = new QgsPanelWidgetStack();
+  mGuideDock->setWidget( mGuideStack );
+  mPanelsMenu->addAction( mGuideDock->toggleViewAction() );
+  connect( mActionManageGuides, &QAction::triggered, this, [ = ]
+  {
+    mGuideDock->setUserVisible( true );
+  } );
+
   addDockWidget( Qt::RightDockWidgetArea, mItemDock );
   addDockWidget( Qt::RightDockWidgetArea, mGeneralDock );
+  addDockWidget( Qt::RightDockWidgetArea, mGuideDock );
 
   createLayoutPropertiesWidget();
 
@@ -317,6 +330,7 @@ void QgsLayoutDesignerDialog::showItemOptions( QgsLayoutItem *item )
   delete mItemPropertiesStack->takeMainPanel();
   widget->setDockMode( true );
   mItemPropertiesStack->setMainPanel( widget.release() );
+  mItemDock->setUserVisible( true );
 }
 
 void QgsLayoutDesignerDialog::open()
@@ -615,13 +629,19 @@ void QgsLayoutDesignerDialog::createLayoutPropertiesWidget()
     return;
   }
 
-  // update composition widget
+  // update layout based widgets
   QgsLayoutPropertiesWidget *oldCompositionWidget = qobject_cast<QgsLayoutPropertiesWidget *>( mGeneralPropertiesStack->takeMainPanel() );
   delete oldCompositionWidget;
+  QgsLayoutGuideWidget *oldGuideWidget = qobject_cast<QgsLayoutGuideWidget *>( mGuideStack->takeMainPanel() );
+  delete oldGuideWidget;
 
   QgsLayoutPropertiesWidget *widget = new QgsLayoutPropertiesWidget( mGeneralDock, mLayout );
   widget->setDockMode( true );
   mGeneralPropertiesStack->setMainPanel( widget );
+
+  QgsLayoutGuideWidget *guideWidget = new QgsLayoutGuideWidget( mGuideDock, mLayout, mView );
+  guideWidget->setDockMode( true );
+  mGuideStack->setMainPanel( guideWidget );
 }
 
 void QgsLayoutDesignerDialog::initializeRegistry()

src/app/layout/qgslayoutdesignerdialog.h

@@ -193,6 +193,8 @@ class QgsLayoutDesignerDialog: public QMainWindow, private Ui::QgsLayoutDesigner
     QgsPanelWidgetStack *mItemPropertiesStack = nullptr;
     QgsDockWidget *mGeneralDock = nullptr;
     QgsPanelWidgetStack *mGeneralPropertiesStack = nullptr;
+    QgsDockWidget *mGuideDock = nullptr;
+    QgsPanelWidgetStack *mGuideStack = nullptr;
 
     //! Save window state
     void saveWindowState();

src/core/layout/qgslayoutguidecollection.cpp

@@ -286,6 +286,12 @@ QgsLayoutGuideProxyModel::QgsLayoutGuideProxyModel( QObject *parent, QgsLayoutGu
   sort( 0 );
 }
 
+void QgsLayoutGuideProxyModel::setPage( int page )
+{
+  mPage = page;
+  invalidateFilter();
+}
+
 bool QgsLayoutGuideProxyModel::filterAcceptsRow( int source_row, const QModelIndex &source_parent ) const
 {
   QModelIndex index = sourceModel()->index( source_row, 0, source_parent );

src/core/layout/qgslayoutguidecollection.h

@@ -175,6 +175,7 @@ class CORE_EXPORT QgsLayoutGuideCollection : public QAbstractListModel
       PositionRole, //!< Guide position role
       UnitsRole, //!< Guide position units role
       PageRole, //!< Guide page role
+      LayoutPositionRole, //!< Guide position in layout coordinates
     };
 
     /**
@@ -234,6 +235,11 @@ class CORE_EXPORT QgsLayoutGuideProxyModel : public QSortFilterProxyModel
      */
     explicit QgsLayoutGuideProxyModel( QObject *parent SIP_TRANSFERTHIS, QgsLayoutGuide::Orientation orientation, int page );
 
+    /**
+     * Sets the current \a page for filtering matching guides. Page numbers begin at 0.
+     */
+    void setPage( int page );
+
     bool filterAcceptsRow( int sourceRow, const QModelIndex &sourceParent ) const override;
     bool lessThan( const QModelIndex &left, const QModelIndex &right ) const override;
 

src/core/layout/qgslayoutsnapper.cpp

@@ -35,6 +35,21 @@ QPointF QgsLayoutSnapper::snapPoint( QPointF point, double scaleFactor, bool &sn
     return res;
   }
 
+  bool snappedToHozGuides = false;
+  double newX = snapPointToGuides( point.x(), QgsLayoutGuide::Vertical, scaleFactor, snappedToHozGuides );
+  if ( snappedToHozGuides )
+  {
+    snapped = true;
+    point.setX( newX );
+  }
+  bool snappedToVertGuides = false;
+  double newY = snapPointToGuides( point.y(), QgsLayoutGuide::Horizontal, scaleFactor, snappedToVertGuides );
+  if ( snappedToVertGuides )
+  {
+    snapped = true;
+    point.setY( newY );
+  }
+
   return point;
 }
 
@@ -88,3 +103,35 @@ QPointF QgsLayoutSnapper::snapPointToGrid( QPointF point, double scaleFactor, bo
 
   return QPointF( xSnapped, ySnapped );
 }
+
+double QgsLayoutSnapper::snapPointToGuides( double original, QgsLayoutGuide::Orientation orientation, double scaleFactor, bool &snapped ) const
+{
+  snapped = false;
+
+  //convert snap tolerance from pixels to layout units
+  double alignThreshold = mTolerance / scaleFactor;
+
+  double bestPos = original;
+  double smallestDiff = DBL_MAX;
+
+  Q_FOREACH ( QgsLayoutGuide *guide, mLayout->guides().guides( orientation ) )
+  {
+    double guidePos = guide->layoutPosition();
+    double diff = qAbs( original - guidePos );
+    if ( diff < smallestDiff )
+    {
+      smallestDiff = diff;
+      bestPos = guidePos;
+    }
+  }
+
+  if ( smallestDiff <= alignThreshold )
+  {
+    snapped = true;
+    return bestPos;
+  }
+  else
+  {
+    return original;
+  }
+}

src/core/layout/qgslayoutsnapper.h

@@ -19,6 +19,7 @@
 #include "qgis_core.h"
 #include "qgslayoutmeasurement.h"
 #include "qgslayoutpoint.h"
+#include "qgslayoutguidecollection.h"
 #include <QPen>
 
 class QgsLayout;
@@ -88,6 +89,19 @@ class CORE_EXPORT QgsLayoutSnapper
      */
     QPointF snapPointToGrid( QPointF point, double scaleFactor, bool &snapped SIP_OUT ) const;
 
+    /**
+     * Snaps a layout coordinate \a point to the grid. If \a point
+     * was snapped, \a snapped will be set to true.
+     *
+     * The \a scaleFactor argument should be set to the transformation from
+     * scalar transform from layout coordinates to pixels, i.e. the
+     * graphics view transform().m11() value.
+     *
+     * If snapToGrid() is disabled, this method will return the point
+     * unchanged.
+     */
+    double snapPointToGuides( double original, QgsLayoutGuide::Orientation orientation, double scaleFactor, bool &snapped SIP_OUT ) const;
+
   private:
 
     QgsLayout *mLayout = nullptr;

src/gui/layout/qgslayoutview.cpp

@@ -61,8 +61,8 @@ void QgsLayoutView::setCurrentLayout( QgsLayout *layout )
 {
   setScene( layout );
 
-  connect( layout->pageCollection(), &QgsLayoutPageCollection::changed, this, &QgsLayoutView::updateRulers );
-  updateRulers();
+  connect( layout->pageCollection(), &QgsLayoutPageCollection::changed, this, &QgsLayoutView::viewChanged );
+  viewChanged();
 
   mSnapMarker.reset( new QgsLayoutViewSnapMarker() );
   mSnapMarker->hide();
@@ -114,7 +114,7 @@ void QgsLayoutView::scaleSafe( double scale )
   scale = qBound( MIN_VIEW_SCALE, scale, MAX_VIEW_SCALE );
   setTransform( QTransform::fromScale( scale, scale ) );
   emit zoomLevelChanged();
-  updateRulers();
+  viewChanged();
 }
 
 void QgsLayoutView::setZoomLevel( double level )
@@ -136,21 +136,21 @@ void QgsLayoutView::setZoomLevel( double level )
     setTransform( QTransform::fromScale( mmLevel, mmLevel ) );
   }
   emit zoomLevelChanged();
-  updateRulers();
+  viewChanged();
 }
 
 void QgsLayoutView::setHorizontalRuler( QgsLayoutRuler *ruler )
 {
   mHorizontalRuler = ruler;
   ruler->setLayoutView( this );
-  updateRulers();
+  viewChanged();
 }
 
 void QgsLayoutView::setVerticalRuler( QgsLayoutRuler *ruler )
 {
   mVerticalRuler = ruler;
   ruler->setLayoutView( this );
-  updateRulers();
+  viewChanged();
 }
 
 void QgsLayoutView::setMenuProvider( QgsLayoutViewMenuProvider *provider )
@@ -166,7 +166,7 @@ QgsLayoutViewMenuProvider *QgsLayoutView::menuProvider() const
 void QgsLayoutView::zoomFull()
 {
   fitInView( scene()->sceneRect(), Qt::KeepAspectRatio );
-  updateRulers();
+  viewChanged();
   emit zoomLevelChanged();
 }
 
@@ -189,7 +189,7 @@ void QgsLayoutView::zoomWidth()
 
   fitInView( targetRect, Qt::KeepAspectRatio );
   emit zoomLevelChanged();
-  updateRulers();
+  viewChanged();
 }
 
 void QgsLayoutView::zoomIn()
@@ -363,15 +363,16 @@ void QgsLayoutView::resizeEvent( QResizeEvent *event )
 {
   QGraphicsView::resizeEvent( event );
   emit zoomLevelChanged();
+  viewChanged();
 }
 
 void QgsLayoutView::scrollContentsBy( int dx, int dy )
 {
   QGraphicsView::scrollContentsBy( dx, dy );
-  updateRulers();
+  viewChanged();
 }
 
-void QgsLayoutView::updateRulers()
+void QgsLayoutView::viewChanged()
 {
   if ( mHorizontalRuler )
   {
@@ -381,6 +382,21 @@ void QgsLayoutView::updateRulers()
   {
     mVerticalRuler->setSceneTransform( viewportTransform() );
   }
+
+  // determine page at center of view
+  QRect viewportRect( 0, 0, viewport()->width(), viewport()->height() );
+  QRectF visibleRect = mapToScene( viewportRect ).boundingRect();
+  QPointF centerVisible = visibleRect.center();
+
+  if ( currentLayout() && currentLayout()->pageCollection() )
+  {
+    int newPage = currentLayout()->pageCollection()->pageNumberForPoint( centerVisible );
+    if ( newPage != mCurrentPage )
+    {
+      mCurrentPage = newPage;
+      emit pageChanged( mCurrentPage );
+    }
+  }
 }
 
 void QgsLayoutView::wheelZoom( QWheelEvent *event )