Reduced memory footprint of QGraphicsWidget.

This commit reduces the memory footprint of QGraphicsWidget by
around 40% (from around 663 bytes to around 409 bytes - measured
using /proc/<pid>/statm on Linux - see 'man 5 proc').

The technique used is to lazily allocate (on the heap) certain
data structures (i.e. not allocate them unless they are needed):

  - QGraphicsLayoutItemPrivate::userSizeHints
    => used only if the size, width, or height is explicitly set

  - QGraphicsWidgetPrivate::margins
    => used only if the contents margins are accessed

  - QGraphicsWidgetPrivate::windowFrameMargins
    => used only if the window frame margins are accessed

  - QGraphicsWidgetPrivate::windowData
    => used only if the graphics widget is a window

In addition, a few unused data members (and related code) were removed:

  - QGraphicsWidgetPrivate::contentsRect
  - QGraphicsWidgetPrivate::mouseDelta
  - QGraphicsWidgetPrivate::*LayoutItemMargin

Reviewed-by: andreas
Task-number: 251592

1 files changed, 6 insertions, 2 deletions

diff --git a/src/gui/graphicsview/qgraphicslayoutitem_p.h b/src/gui/graphicsview/qgraphicslayoutitem_p.h
index fab0f39..dc044e6 100644
--- a/src/gui/graphicsview/qgraphicslayoutitem_p.h
+++ b/src/gui/graphicsview/qgraphicslayoutitem_p.h
@@ -63,16 +63,20 @@ class Q_AUTOTEST_EXPORT QGraphicsLayoutItemPrivate
 {
     Q_DECLARE_PUBLIC(QGraphicsLayoutItem)
 public:
-    virtual ~QGraphicsLayoutItemPrivate() {}
+    virtual ~QGraphicsLayoutItemPrivate();
     QGraphicsLayoutItemPrivate(QGraphicsLayoutItem *parent, bool isLayout);
     void init();
     QSizeF *effectiveSizeHints(const QSizeF &constraint) const;
     QGraphicsItem *parentItem() const;
+    void ensureUserSizeHints();
+    void setSize(Qt::SizeHint which, const QSizeF &size);
+    enum SizeComponent { Width, Height };
+    void setSizeComponent(Qt::SizeHint which, SizeComponent component, qreal value);
 
     QSizePolicy sizePolicy;
     QGraphicsLayoutItem *parent;
 
-    QSizeF userSizeHints[Qt::NSizeHints];
+    QSizeF *userSizeHints;
     mutable QSizeF cachedSizeHints[Qt::NSizeHints];
     mutable QSizeF cachedConstraint;