[needs-docs] Partial WIP of dragging rulers to create guide lines

Unlike in 2.x, Layouts in 3.0 adopt the standard UX of dragging
out rulers to create guide lines (instead of clicking on a ruler
position to create a guide)

python/gui/layout/qgslayoutruler.sip

@@ -72,6 +72,10 @@ class QgsLayoutRuler: QWidget
 
     virtual void mouseMoveEvent( QMouseEvent *event );
 
+    virtual void mousePressEvent( QMouseEvent *event );
+
+    virtual void mouseReleaseEvent( QMouseEvent *event );
+
 
   signals:
     void cursorPosChanged( QPointF );

src/core/layout/qgslayoutguidecollection.cpp

@@ -80,7 +80,7 @@ void QgsLayoutGuide::update()
   switch ( mOrientation )
   {
     case Horizontal:
-      if ( layoutPos > page->rect().width() )
+      if ( layoutPos > page->rect().height() )
       {
         mLineItem->hide();
       }
@@ -93,7 +93,7 @@ void QgsLayoutGuide::update()
       break;
 
     case Vertical:
-      if ( layoutPos > page->rect().height() )
+      if ( layoutPos > page->rect().width() )
       {
         mLineItem->hide();
       }

src/gui/layout/qgslayoutruler.cpp

@@ -428,22 +428,118 @@ void QgsLayoutRuler::mouseMoveEvent( QMouseEvent *event )
   mMarkerPos = event->posF();
   update();
 
-  //update cursor position in status bar
-  QPointF displayPos = mTransform.inverted().map( event->posF() );
-  switch ( mOrientation )
+  QPointF displayPos;
+  if ( mCreatingGuide )
   {
-    case Qt::Horizontal:
+    // event -> layout coordinates
+    QgsLayout *layout = mView->currentLayout();
+    QPoint viewPoint  = mView->mapFromGlobal( mapToGlobal( event->pos() ) );
+    displayPos = mView->mapToScene( viewPoint );
+    int pageNo = layout->pageCollection()->pageNumberForPoint( displayPos );
+    QgsLayoutItemPage *page = layout->pageCollection()->page( pageNo );
+
+    switch ( mOrientation )
     {
-      //mouse is over a horizontal ruler, so don't show a y coordinate
-      displayPos.setY( 0 );
-      break;
+      case Qt::Horizontal:
+      {
+        //mouse is creating a horizontal ruler, so don't show x coordinate
+        mGuideItem->setLine( 0, displayPos.y(), page->rect().width(), displayPos.y() );
+        displayPos.setX( 0 );
+        break;
+      }
+      case Qt::Vertical:
+      {
+        //mouse is creating a vertical ruler, so don't show a y coordinate
+        mGuideItem->setLine( displayPos.x(), 0, displayPos.x(), page->rect().height() );
+        displayPos.setY( 0 );
+        break;
+      }
     }
-    case Qt::Vertical:
+  }
+  else
+  {
+    //update cursor position in status bar
+    displayPos = mTransform.inverted().map( event->posF() );
+    switch ( mOrientation )
     {
-      //mouse is over a vertical ruler, so don't show an x coordinate
-      displayPos.setX( 0 );
-      break;
+      case Qt::Horizontal:
+      {
+        //mouse is over a horizontal ruler, so don't show a y coordinate
+        displayPos.setY( 0 );
+        break;
+      }
+      case Qt::Vertical:
+      {
+        //mouse is over a vertical ruler, so don't show an x coordinate
+        displayPos.setX( 0 );
+        break;
+      }
     }
   }
   emit cursorPosChanged( displayPos );
 }
+
+void QgsLayoutRuler::mousePressEvent( QMouseEvent *event )
+{
+  if ( event->button() == Qt::LeftButton )
+  {
+    mCreatingGuide = true;
+    mGuideItem.reset( new QGraphicsLineItem() );
+
+    mGuideItem->setZValue( QgsLayout::ZGuide );
+    QPen linePen( Qt::DashLine );
+    linePen.setColor( Qt::red );
+    linePen.setWidthF( 0 );
+    mGuideItem->setPen( linePen );
+
+    mView->currentLayout()->addItem( mGuideItem.get() );
+
+    switch ( mOrientation )
+    {
+      case Qt::Horizontal:
+      {
+        QApplication::setOverrideCursor( Qt::SplitVCursor );
+        break;
+      }
+      case Qt::Vertical:
+        QApplication::setOverrideCursor( Qt::SplitHCursor );
+        break;
+    }
+  }
+}
+
+void QgsLayoutRuler::mouseReleaseEvent( QMouseEvent *event )
+{
+  if ( event->button() == Qt::LeftButton )
+  {
+    mCreatingGuide = false;
+    QApplication::restoreOverrideCursor();
+    mGuideItem.reset();
+
+    QgsLayout *layout = mView->currentLayout();
+
+    // create guide
+    QPoint viewPoint  = mView->mapFromGlobal( mapToGlobal( event->pos() ) );
+    QPointF scenePos = mView->mapToScene( viewPoint );
+    int page = layout->pageCollection()->pageNumberForPoint( scenePos );
+    std::unique_ptr< QgsLayoutGuide > guide;
+    switch ( mOrientation )
+    {
+      case Qt::Horizontal:
+      {
+        //mouse is creating a horizontal guide
+        double posOnPage = layout->pageCollection()->positionOnPage( scenePos ).y();
+        guide.reset( new QgsLayoutGuide( QgsLayoutGuide::Horizontal, QgsLayoutMeasurement( posOnPage, layout->units() ) ) );
+        break;
+      }
+      case Qt::Vertical:
+      {
+        //mouse is creating a vertical guide
+        guide.reset( new QgsLayoutGuide( QgsLayoutGuide::Vertical, QgsLayoutMeasurement( scenePos.x(), layout->units() ) ) );
+        break;
+      }
+    }
+    guide->setPage( page );
+    mView->currentLayout()->guides().addGuide( guide.release() );
+  }
+}

src/gui/layout/qgslayoutruler.h

@@ -81,6 +81,8 @@ class GUI_EXPORT QgsLayoutRuler: public QWidget
   protected:
     void paintEvent( QPaintEvent *event ) override;
     void mouseMoveEvent( QMouseEvent *event ) override;
+    void mousePressEvent( QMouseEvent *event ) override;
+    void mouseReleaseEvent( QMouseEvent *event ) override;
 
   private:
     static const int VALID_SCALE_MULTIPLES[];
@@ -102,6 +104,9 @@ class GUI_EXPORT QgsLayoutRuler: public QWidget
     int mTextBaseline;
     int mMinSpacingVerticalLabels;
 
+    bool mCreatingGuide = false;
+    std::unique_ptr< QGraphicsLineItem > mGuideItem;
+
     //! Calculates the optimum labeled units for ruler so that labels are a good distance apart
     int optimumScale( double minPixelDiff, int &magnitude, int &multiple );