QskViewportChange events added ( using the QQuickItem::ItemObservesViewport

concept )

examples/thumbnails/main.cpp

@@ -26,8 +26,6 @@
 
 #include <cstdlib>
 
-#define HIDE_NODES 1
-
 const int gridSize = 20;
 const int thumbnailSize = 150;
 
@@ -81,18 +79,6 @@ class Thumbnail : public QskPushButton
         setStrutSizeHint( QskPushButton::Icon, -1, -1 );
     }
 
-#if 0
-    void mousePressEvent( QMouseEvent* event ) override
-    {
-        /*
-            ignore events: to check if the pan gesture recoognizer of the scroll
-            area works, when the event arrives as regular event
-            ( not via childMouseEventFilter )
-         */
-        event->setAccepted( false );
-    }
-#endif
-
   private:
     QskGraphic thumbnailGraphic( const QColor& color,
         int shape, const QSizeF& size ) const
@@ -124,54 +110,67 @@ class IconGrid : public QskLinearBox
     IconGrid( QQuickItem* parentItem = nullptr )
         : QskLinearBox( Qt::Horizontal, gridSize, parentItem )
     {
+#if QT_VERSION >= QT_VERSION_CHECK( 6, 3, 0 )
+        setFlag( QQuickItem::ItemObservesViewport, true );
+#endif
+
         setMargins( 20 );
         setSpacing( 20 );
 
         for ( int col = 0; col < gridSize; col++ )
         {
             for ( int row = 0; row < gridSize; row++ )
-                ( void ) new Thumbnail( randomColor(), randomShape(), this );
+            {
+                auto thumbnail = new Thumbnail( randomColor(), randomShape(), this );
+                thumbnail->setPlacementPolicy( Qsk::Hidden, QskPlacementPolicy::Reserve );
+                thumbnail->setVisible( false );
+            }
         }
 
-#if HIDE_NODES
+        setSize( sizeConstraint() );
+    }
+
+  protected:
+    void viewportChangeEvent( QskViewportChangeEvent* ) override
+    {
+        if ( isEmpty() )
+            return;
+
         /*
             When having too many nodes, the scene graph becomes horribly slow.
             So we explicitely hide all items outside the visible area
             ( see updateVisibilities below ) and make use of the DeferredUpdate and
             CleanupOnVisibility features of QskItem.
          */
-        setSize( sizeConstraint() );
-        updateLayout(); // so that every item has its initial geometry
 
-        for ( int i = 0; i < elementCount(); i++ )
-        {
-            if ( auto control = qskControlCast( itemAtIndex( i ) ) )
-            {
-                // to support the optimizations in ScrollArea::updateVisibilities
-                control->setPlacementPolicy( Qsk::Hidden, QskPlacementPolicy::Reserve );
-                control->setVisible( false );
-            }
-        }
+        QQuickItem* item;
+
+#if QT_VERSION >= QT_VERSION_CHECK( 6, 3, 0 )
+        item = viewportItem();
+#else
+        for ( item = parentItem(); item && !item->clip(); item = item->parentItem() );
 #endif
-    }
 
-#if HIDE_NODES
-    void updateVisibilities( const QRectF& viewPort )
-    {
-        if ( !isEmpty() && viewPort != m_viewPort )
+        if ( item )
         {
-            setItemsVisible( m_viewPort, false );
-            setItemsVisible( viewPort, true );
+            auto r = item->clipRect();
+            r.moveTo( mapFromItem( item, r.topLeft() ) );
 
-            m_viewPort = viewPort;
+            const auto viewPort = this->viewPort( r );
+
+            if ( m_viewPort != viewPort )
+            {
+                setItemsVisible( m_viewPort, false );
+                setItemsVisible( viewPort, true );
+
+                m_viewPort = viewPort;
+            }
         }
     }
 
   private:
-    void setItemsVisible( const QRectF& rect, bool on )
+    QRect viewPort( const QRectF& rect ) const
     {
-        const auto dim = dimension();
-
         // we know, that all items have the same size
         const auto itemSize = itemAtIndex( 0 )->size();
 
@@ -181,9 +180,16 @@ class IconGrid : public QskLinearBox
         const int colMin = rect.left() / ( itemSize.width() + spacing() );
         const int colMax = rect.right() / ( itemSize.height() + spacing() );
 
-        for ( int row = rowMin; row <= rowMax; row++ )
+        return QRect( colMin, rowMin, colMax - colMin + 1, rowMax - rowMin + 1 );
+    }
+
+    void setItemsVisible( const QRect& viewPort, bool on )
+    {
+        const auto dim = dimension();
+
+        for ( int row = viewPort.top(); row <= viewPort.bottom(); row++ )
         {
-            for ( int col = colMin; col <= colMax; col++ )
+            for ( int col = viewPort.left(); col <= viewPort.right(); col++ )
             {
                 if ( auto item = itemAtIndex( row * dim + col ) )
                     item->setVisible( on );
@@ -191,8 +197,7 @@ class IconGrid : public QskLinearBox
         }
     }
 
-    QRectF m_viewPort;
-#endif
+    QRect m_viewPort;
 };
 
 class ScrollArea : public QskScrollArea
@@ -218,29 +223,6 @@ class ScrollArea : public QskScrollArea
         setBoxShapeHint( HorizontalScrollHandle, 8 );
 
         setFlickRecognizerTimeout( 300 );
-
-        connect( this, &QskScrollView::scrollPosChanged,
-            this, &ScrollArea::updateVisibilities );
-    }
-
-  protected:
-    void geometryChangeEvent( QskGeometryChangeEvent* event ) override
-    {
-        QskScrollArea::geometryChangeEvent( event );
-        updateVisibilities();
-    }
-
-  private:
-    void updateVisibilities()
-    {
-#if HIDE_NODES
-        const auto box = static_cast< IconGrid* >( scrolledItem() );
-        if ( box )
-        {
-            const QRectF viewPort( scrollPos(), viewContentsRect().size() );
-            box->updateVisibilities( viewPort );
-        }
-#endif
     }
 };
 
@@ -291,7 +273,7 @@ int main( int argc, char* argv[] )
     scrollArea->setScrolledItem( iconGrid );
 
 #if 0
-    // for testing nested gestures 
+    // for testing nested gestures
     auto swipeView = new QskSwipeView();
 
     swipeView->addItem( scrollArea );

src/controls/QskEvent.cpp

@@ -189,6 +189,7 @@ QskEvent* QskEvent::clone() const
 }
 
 #endif
+
 // -- QskGeometryChangeEvent
 
 QskGeometryChangeEvent::QskGeometryChangeEvent(
@@ -216,6 +217,19 @@ bool QskGeometryChangeEvent::isMoved() const
         ( m_rect.y() != m_oldRect.y() );
 }
 
+// -- QskViewportChangeEvent
+
+QskViewportChangeEvent::QskViewportChangeEvent( QQuickItem* modifiedParent )
+    : QskEvent( QskEvent::ViewportChange )
+    , m_modifiedParent( modifiedParent )
+{
+}
+
+QskViewportChangeEvent* QskViewportChangeEvent::clone() const
+{
+    return new QskViewportChangeEvent( *this );
+}
+
 // -- QskWindowChangeEvent
 
 QskWindowChangeEvent::QskWindowChangeEvent(

src/controls/QskEvent.h

@@ -37,6 +37,7 @@ class QSK_EXPORT QskEvent : public QEvent
         NoEvent = 53800,
 
         GeometryChange,
+        ViewportChange,
         WindowChange,
 
         /*
@@ -85,6 +86,22 @@ class QSK_EXPORT QskGeometryChangeEvent : public QskEvent
     QRectF m_oldRect;
 };
 
+class QSK_EXPORT QskViewportChangeEvent : public QskEvent
+{
+  public:
+    QskViewportChangeEvent( QQuickItem* );
+
+    inline QQuickItem* modifiedParent() const { return m_modifiedParent; }
+
+    QskViewportChangeEvent* clone() const override;
+
+  protected:
+    QSK_EVENT_DISABLE_COPY( QskViewportChangeEvent )
+
+  private:
+    QQuickItem* m_modifiedParent;
+};
+
 class QSK_EXPORT QskWindowChangeEvent : public QskEvent
 {
   public:

src/controls/QskItem.cpp

@@ -781,6 +781,11 @@ bool QskItem::event( QEvent* event )
             changeEvent( event );
             return true;
         }
+        case QskEvent::ViewportChange:
+        {
+            viewportChangeEvent( static_cast< QskViewportChangeEvent* >( event ) );
+            return true;
+        }
         case QskEvent::GeometryChange:
         {
             geometryChangeEvent( static_cast< QskGeometryChangeEvent* >( event ) );
@@ -858,6 +863,11 @@ void QskItem::windowChangeEvent( QskWindowChangeEvent* )
 {
 }
 
+void QskItem::viewportChangeEvent( QskViewportChangeEvent* event )
+{
+    event->ignore();
+}
+
 void QskItem::geometryChangeEvent( QskGeometryChangeEvent* )
 {
 }

src/controls/QskItem.h

@@ -11,6 +11,7 @@
 
 class QskItemPrivate;
 class QskGeometryChangeEvent;
+class QskViewportChangeEvent;
 class QskWindowChangeEvent;
 
 class QSK_EXPORT QskItem : public QQuickItem
@@ -154,6 +155,7 @@ class QSK_EXPORT QskItem : public QQuickItem
 
     virtual void changeEvent( QEvent* );
     virtual void geometryChangeEvent( QskGeometryChangeEvent* );
+    virtual void viewportChangeEvent( QskViewportChangeEvent* );
     virtual void windowChangeEvent( QskWindowChangeEvent* );
 
     void mouseUngrabEvent() override;

src/controls/QskItemPrivate.cpp

@@ -6,6 +6,7 @@
 #include "QskItemPrivate.h"
 #include "QskTreeNode.h"
 #include "QskSetup.h"
+#include "QskEvent.h"
 
 static inline void qskSendEventTo( QObject* object, QEvent::Type type )
 {
@@ -251,8 +252,24 @@ QSGTransformNode* QskItemPrivate::createTransformNode()
     return new QskItemNode();
 }
 
-/*
-    Can we do something useful with overloading:
+#if QT_VERSION >= QT_VERSION_CHECK( 6, 3, 0 )
 
-        - QQuickItemPrivate::transformChanged
- */
+bool QskItemPrivate::transformChanged( QQuickItem* transformedItem )
+{
+    bool accepted = false;
+
+    if ( q_func()->flags() & QQuickItem::ItemObservesViewport )
+    {
+        QskViewportChangeEvent event( transformedItem );
+        QCoreApplication::sendEvent( q_func(), &event );
+
+        accepted = event.isAccepted();
+    }
+
+    accepted |= Inherited::transformChanged( transformedItem );
+
+
+    return accepted;
+}
+
+#endif

src/controls/QskItemPrivate.h

@@ -45,6 +45,10 @@ class QskItemPrivate : public QQuickItemPrivate
     void setImplicitSize( qreal width, qreal height, bool doNotify );
     virtual QSizeF implicitSizeHint() const = 0;
 
+#if QT_VERSION >= QT_VERSION_CHECK( 6, 3, 0 )
+    bool transformChanged( QQuickItem* ) override final;
+#endif
+
   private:
     Q_DECLARE_PUBLIC( QskItem )
 

src/controls/QskScrollArea.cpp

@@ -245,6 +245,8 @@ namespace
         {
             if ( change.sizeChange() )
                 scrolledItemGeometryChange();
+
+            viewportChanged();
         }
 
         void updateNode( QSGNode* ) override;
@@ -287,6 +289,17 @@ namespace
 
         const QSGClipNode* viewPortClipNode() const;
 
+        void viewportChanged()
+        {
+#if QT_VERSION < QT_VERSION_CHECK( 6, 3, 0 )
+            if ( auto item = scrollArea()->scrolledItem() )
+            {
+                QskViewportChangeEvent ev( this );
+                QCoreApplication::sendEvent( item, &ev );
+            }
+#endif
+        }
+
         bool m_isSizeChangedEnabled = true;
     };
 
@@ -422,6 +435,7 @@ namespace
             {
                 // we need to restore the clip node
                 update();
+                viewportChanged();
             }
         }