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, 78 insertions, 56 deletions

diff --git a/src/gui/graphicsview/qgraphicslayoutitem.cpp b/src/gui/graphicsview/qgraphicslayoutitem.cpp
index eaa97ff..e058292 100644
--- a/src/gui/graphicsview/qgraphicslayoutitem.cpp
+++ b/src/gui/graphicsview/qgraphicslayoutitem.cpp
@@ -108,13 +108,22 @@ static void normalizeHints(qreal &minimum, qreal &preferred, qreal &maximum, qre
     \internal
 */
 QGraphicsLayoutItemPrivate::QGraphicsLayoutItemPrivate(QGraphicsLayoutItem *par, bool layout)
-    : parent(par), isLayout(layout), ownedByLayout(false), graphicsItem(0)
+    : parent(par), userSizeHints(0), isLayout(layout), ownedByLayout(false), graphicsItem(0)
 {
 }
 
 /*!
     \internal
 */
+QGraphicsLayoutItemPrivate::~QGraphicsLayoutItemPrivate()
+{
+    // Remove any lazily allocated data
+    delete[] userSizeHints;
+}
+
+/*!
+    \internal
+*/
 void QGraphicsLayoutItemPrivate::init()
 {
     sizeHintCacheDirty = true;
@@ -132,7 +141,8 @@ QSizeF *QGraphicsLayoutItemPrivate::effectiveSizeHints(const QSizeF &constraint)
 
     for (int i = 0; i < Qt::NSizeHints; ++i) {
         cachedSizeHints[i] = constraint;
-        combineSize(cachedSizeHints[i], userSizeHints[i]);
+        if (userSizeHints)
+            combineSize(cachedSizeHints[i], userSizeHints[i]);
     }
 
     QSizeF &minS = cachedSizeHints[Qt::MinimumSize];
@@ -198,6 +208,58 @@ QGraphicsItem *QGraphicsLayoutItemPrivate::parentItem() const
 }
 
 /*!
+    \internal
+
+     Ensures that userSizeHints is allocated.
+     This function must be called before any dereferencing.
+*/
+void QGraphicsLayoutItemPrivate::ensureUserSizeHints()
+{
+    if (!userSizeHints)
+        userSizeHints = new QSizeF[Qt::NSizeHints];
+}
+
+/*!
+    \internal
+
+    Sets the user size hint \a which to \a size. Use an invalid size to unset the size hint.
+ */
+void QGraphicsLayoutItemPrivate::setSize(Qt::SizeHint which, const QSizeF &size)
+{
+    Q_Q(QGraphicsLayoutItem);
+
+    if (userSizeHints) {
+        if (size == userSizeHints[which])
+            return;
+    } else if (!size.isValid()) {
+        return;
+    }
+
+    ensureUserSizeHints();
+    userSizeHints[which] = size;
+    q->updateGeometry();
+}
+
+/*!
+    \internal
+
+    Sets the width of the user size hint \a which to \a width.
+ */
+void QGraphicsLayoutItemPrivate::setSizeComponent(
+    Qt::SizeHint which, SizeComponent component, qreal value)
+{
+    Q_Q(QGraphicsLayoutItem);
+    ensureUserSizeHints();
+    qreal &userValue = (component == Width)
+        ? userSizeHints[which].rwidth()
+        : userSizeHints[which].rheight();
+    if (value == userValue)
+        return;
+    userValue = value;
+    q->updateGeometry();
+}
+
+/*!
     \class QGraphicsLayoutItem
     \brief The QGraphicsLayoutItem class can be inherited to allow your custom
     items to be managed by layouts.
@@ -381,12 +443,7 @@ QSizePolicy QGraphicsLayoutItem::sizePolicy() const
 */
 void QGraphicsLayoutItem::setMinimumSize(const QSizeF &size)
 {
-    Q_D(QGraphicsLayoutItem);
-    if (size == d->userSizeHints[Qt::MinimumSize])
-        return;
-
-    d->userSizeHints[Qt::MinimumSize] = size;
-    updateGeometry();
+    d_ptr->setSize(Qt::MinimumSize, size);
 }
 
 /*!
@@ -416,12 +473,7 @@ QSizeF QGraphicsLayoutItem::minimumSize() const
 */
 void QGraphicsLayoutItem::setMinimumWidth(qreal width)
 {
-    Q_D(QGraphicsLayoutItem);
-    qreal &userSizeHint = d->userSizeHints[Qt::MinimumSize].rwidth();
-    if (width == userSizeHint)
-        return;
-    userSizeHint = width;
-    updateGeometry();
+    d_ptr->setSizeComponent(Qt::MinimumSize, d_ptr->Width, width);
 }
 
 /*!
@@ -431,12 +483,7 @@ void QGraphicsLayoutItem::setMinimumWidth(qreal width)
 */
 void QGraphicsLayoutItem::setMinimumHeight(qreal height)
 {
-    Q_D(QGraphicsLayoutItem);
-    qreal &userSizeHint = d->userSizeHints[Qt::MinimumSize].rheight();
-    if (height == userSizeHint)
-        return;
-    userSizeHint = height;
-    updateGeometry();
+    d_ptr->setSizeComponent(Qt::MinimumSize, d_ptr->Height, height);
 }
 
 
@@ -450,12 +497,7 @@ void QGraphicsLayoutItem::setMinimumHeight(qreal height)
 */
 void QGraphicsLayoutItem::setPreferredSize(const QSizeF &size)
 {
-    Q_D(QGraphicsLayoutItem);
-    if (size == d->userSizeHints[Qt::PreferredSize])
-        return;
-
-    d->userSizeHints[Qt::PreferredSize] = size;
-    updateGeometry();
+    d_ptr->setSize(Qt::PreferredSize, size);
 }
 
 /*!
@@ -485,12 +527,7 @@ QSizeF QGraphicsLayoutItem::preferredSize() const
 */
 void QGraphicsLayoutItem::setPreferredHeight(qreal height)
 {
-    Q_D(QGraphicsLayoutItem);
-    qreal &userSizeHint = d->userSizeHints[Qt::PreferredSize].rheight();
-    if (height == userSizeHint)
-        return;
-    userSizeHint = height;
-    updateGeometry();
+    d_ptr->setSizeComponent(Qt::PreferredSize, d_ptr->Height, height);
 }
 
 /*!
@@ -500,12 +537,7 @@ void QGraphicsLayoutItem::setPreferredHeight(qreal height)
 */
 void QGraphicsLayoutItem::setPreferredWidth(qreal width)
 {
-    Q_D(QGraphicsLayoutItem);
-    qreal &userSizeHint = d->userSizeHints[Qt::PreferredSize].rwidth();
-    if (width == userSizeHint)
-        return;
-    userSizeHint = width;
-    updateGeometry();
+    d_ptr->setSizeComponent(Qt::PreferredSize, d_ptr->Width, width);
 }
 
 /*!
@@ -519,12 +551,7 @@ void QGraphicsLayoutItem::setPreferredWidth(qreal width)
 */
 void QGraphicsLayoutItem::setMaximumSize(const QSizeF &size)
 {
-    Q_D(QGraphicsLayoutItem);
-    if (size == d->userSizeHints[Qt::MaximumSize])
-        return;
-
-    d->userSizeHints[Qt::MaximumSize] = size;
-    updateGeometry();
+    d_ptr->setSize(Qt::MaximumSize, size);
 }
 
 /*!
@@ -554,12 +581,7 @@ QSizeF QGraphicsLayoutItem::maximumSize() const
 */
 void QGraphicsLayoutItem::setMaximumWidth(qreal width)
 {
-    Q_D(QGraphicsLayoutItem);
-    qreal &userSizeHint = d->userSizeHints[Qt::MaximumSize].rwidth();
-    if (width == userSizeHint)
-        return;
-    userSizeHint = width;
-    updateGeometry();
+    d_ptr->setSizeComponent(Qt::MaximumSize, d_ptr->Width, width);
 }
 
 /*!
@@ -569,12 +591,7 @@ void QGraphicsLayoutItem::setMaximumWidth(qreal width)
 */
 void QGraphicsLayoutItem::setMaximumHeight(qreal height)
 {
-    Q_D(QGraphicsLayoutItem);
-    qreal &userSizeHint = d->userSizeHints[Qt::MaximumSize].rheight();
-    if (height == userSizeHint)
-        return;
-    userSizeHint = height;
-    updateGeometry();
+    d_ptr->setSizeComponent(Qt::MaximumSize, d_ptr->Height, height);
 }
 
 /*!
@@ -732,6 +749,11 @@ QRectF QGraphicsLayoutItem::contentsRect() const
 */
 QSizeF QGraphicsLayoutItem::effectiveSizeHint(Qt::SizeHint which, const QSizeF &constraint) const
 {
+    Q_D(const QGraphicsLayoutItem);
+
+    if (!d->userSizeHints && constraint.isValid())
+        return constraint;
+
     // ### should respect size policy???
     return d_ptr->effectiveSizeHints(constraint)[which];
 }