Introduce QGraphicsLayoutItem::isEmpty()

This change does basically two things:
* Renames QGraphicsGridLayoutEngineItem::isIgnored() to
  QGraphicsGridLayoutEngineItem::isEmpty() to be consistent with
  QLayoutItem::isEmpty()

* Creates a new public API function QGraphicsLayoutItem::isEmpty() so
  that there is a public method of overriding the behavior.

Change-Id: I771a8fb429f9764a75e220f0ff9d07f578f981d3
Reviewed-by: Paul Olav Tvete <paul.tvete@qt.io>

src/gui/util/qgridlayoutengine.cpp

@@ -1336,7 +1336,7 @@ void QGridLayoutEngine::fillRowData(QGridLayoutRowData *rowData,
             if (rowIsIdenticalToPrevious && item != itemAt(row - 1, column, orientation))
                 rowIsIdenticalToPrevious = false;
 
-            if (item && !item->isIgnored())
+            if (item && !item->isEmpty())
                 rowIsEmpty = false;
         }
 

src/gui/util/qgridlayoutengine_p.h

@@ -303,7 +303,7 @@ public:
 
     virtual QLayoutPolicy::Policy sizePolicy(Qt::Orientation orientation) const = 0;
     virtual QSizeF sizeHint(Qt::SizeHint which, const QSizeF &constraint) const = 0;
-    virtual bool isIgnored() const { return false; }
+    virtual bool isEmpty() const { return false; }
 
     virtual void setGeometry(const QRectF &rect) = 0;
     /*

src/widgets/graphicsview/qgraphicsgridlayoutengine.cpp

@@ -42,29 +42,9 @@
 #include "qgraphicslayoutitem_p.h"
 #include "qgraphicslayout_p.h"
 #include "qgraphicswidget.h"
-#include <private/qgraphicswidget_p.h>
 
 QT_BEGIN_NAMESPACE
 
-bool QGraphicsGridLayoutEngineItem::isHidden() const
-{
-    if (QGraphicsItem *item = q_layoutItem->graphicsItem())
-        return QGraphicsItemPrivate::get(item)->explicitlyHidden;
-    return false;
-}
-
-/*!
-  \internal
-
-  If this returns true, the layout will arrange just as if the item was never added to the layout.
-  (Note that this shouldn't lead to a "double spacing" where the item was hidden)
-  ### Qt6: Move to QGraphicsLayoutItem and make virtual
-*/
-bool QGraphicsGridLayoutEngineItem::isIgnored() const
-{
-    return isHidden() && !q_layoutItem->sizePolicy().retainSizeWhenHidden();
-}
-
 /*
   returns \c true if the size policy returns \c true for either hasHeightForWidth()
   or hasWidthForHeight()
@@ -83,6 +63,16 @@ Qt::Orientation QGraphicsGridLayoutEngineItem::dynamicConstraintOrientation() co
         return Qt::Horizontal;
 }
 
+/*!
+  \internal
+
+  If this returns true, the layout will arrange just as if the item was never added to the layout.
+  (Note that this shouldn't lead to a "double spacing" where the item was hidden)
+*/
+bool QGraphicsGridLayoutEngineItem::isEmpty() const
+{
+    return q_layoutItem->isEmpty();
+}
 
 void QGraphicsGridLayoutEngine::setAlignment(QGraphicsLayoutItem *graphicsLayoutItem, Qt::Alignment alignment)
 {

src/widgets/graphicsview/qgraphicsgridlayoutengine_p.h

@@ -89,10 +89,6 @@ public:
         return q_layoutItem->effectiveSizeHint(which, constraint);
     }
 
-    bool isHidden() const;
-
-    virtual bool isIgnored() const override;
-
     virtual void setGeometry(const QRectF &rect) override
     {
          q_layoutItem->setGeometry(rect);
@@ -101,6 +97,8 @@ public:
     virtual bool hasDynamicConstraint() const override;
     virtual Qt::Orientation dynamicConstraintOrientation() const override;
 
+    virtual bool isEmpty() const override;
+
     QGraphicsLayoutItem *layoutItem() const { return q_layoutItem; }
 
 protected:

src/widgets/graphicsview/qgraphicslayoutitem.cpp

@@ -45,6 +45,7 @@
 #include "qgraphicslayoutitem_p.h"
 #include "qwidget.h"
 #include "qgraphicswidget.h"
+#include "qgraphicsitem_p.h"
 
 #include <QtDebug>
 
@@ -825,6 +826,22 @@ void QGraphicsLayoutItem::updateGeometry()
     d->sizeHintWithConstraintCacheDirty = true;
 }
 
+/*!
+ * returns \c true if this item is empty, i.e whether it has no content and
+ * should not occupy any space.
+ *
+ * The default implementation returns true if the item has been hidden unless
+ * its size policy has retainSizeWhenHidden set to \c true
+ */
+bool QGraphicsLayoutItem::isEmpty() const
+{
+    bool isHidden = false;
+    if (QGraphicsItem *item = graphicsItem())
+        isHidden = QGraphicsItemPrivate::get(item)->explicitlyHidden;
+
+    return isHidden && !sizePolicy().retainSizeWhenHidden();
+}
+
 /*!
     Returns the parent of this QGraphicsLayoutItem, or \nullptr if there is
     no parent, or if the parent does not inherit from QGraphicsLayoutItem

src/widgets/graphicsview/qgraphicslayoutitem.h

@@ -94,6 +94,7 @@ public:
 
     virtual void updateGeometry();
 
+    virtual bool isEmpty() const;
     QGraphicsLayoutItem *parentLayoutItem() const;
     void setParentLayoutItem(QGraphicsLayoutItem *parent);