QQuickPane: calculate content size in C++ unless explicitly defined

No more need for the clumsy and slow contentWidth and contentHeight
bindings in Pane and its derivatives.

QmlBench on TX1:

    Pane: 26.4 -> 32.8 frames (~24%)
    Frame: 25.4 -> 31 frames (~22%)
    GroupBox: 28.6 -> 32 frames (~12%)

Change-Id: I4ba1d46ba6328de2ee0955c241d4b090127f6b85
Reviewed-by: Mitch Curtis <mitch.curtis@qt.io>

3 files changed, 173 insertions, 8 deletions

diff --git a/src/quicktemplates2/qquickpane.cpp b/src/quicktemplates2/qquickpane.cpp
index 4c3e1422..7de0e1c5 100644
--- a/src/quicktemplates2/qquickpane.cpp
+++ b/src/quicktemplates2/qquickpane.cpp
@@ -104,8 +104,12 @@ QT_BEGIN_NAMESPACE
     \sa {Customizing Pane}, {Container Controls}
 */
 
+static const QQuickItemPrivate::ChangeTypes ImplicitSizeChanges = QQuickItemPrivate::ImplicitWidth | QQuickItemPrivate::ImplicitHeight | QQuickItemPrivate::Destroyed;
+
 QQuickPanePrivate::QQuickPanePrivate()
-    : contentWidth(0),
+    : hasContentWidth(false),
+      hasContentHeight(false),
+      contentWidth(0),
       contentHeight(0)
 {
 }
@@ -118,6 +122,112 @@ QQuickItem *QQuickPanePrivate::getContentItem()
     return new QQuickItem(q);
 }
 
+void QQuickPanePrivate::addImplicitSizeListener(QQuickItem *item)
+{
+    if (!item)
+        return;
+
+    QQuickItemPrivate::get(item)->addItemChangeListener(this, ImplicitSizeChanges);
+}
+
+void QQuickPanePrivate::removeImplicitSizeListener(QQuickItem *item)
+{
+    if (!item)
+        return;
+
+    QQuickItemPrivate::get(item)->removeItemChangeListener(this, ImplicitSizeChanges);
+}
+
+void QQuickPanePrivate::itemImplicitWidthChanged(QQuickItem *item)
+{
+    Q_Q(QQuickPane);
+    if (item == contentItem && updateContentWidth(item))
+        emit q->contentWidthChanged();
+}
+
+void QQuickPanePrivate::itemImplicitHeightChanged(QQuickItem *item)
+{
+    Q_Q(QQuickPane);
+    if (item == contentItem && updateContentHeight(item))
+        emit q->contentHeightChanged();
+}
+
+void QQuickPanePrivate::itemDestroyed(QQuickItem *item)
+{
+    if (item == contentItem)
+        updateContentSize(nullptr);
+}
+
+void QQuickPanePrivate::contentChildrenChange()
+{
+    Q_Q(QQuickPane);
+    updateContentSize(contentItem);
+    emit q->contentChildrenChanged();
+}
+
+static qreal getContentWidth(QQuickItem *item)
+{
+    if (!item)
+        return 0;
+
+    const qreal cw = item->implicitWidth();
+    if (!qFuzzyIsNull(cw))
+        return cw;
+
+    const auto contentChildren = item->childItems();
+    if (contentChildren.count() == 1)
+        return contentChildren.first()->implicitWidth();
+
+    return 0;
+}
+
+static qreal getContentHeight(QQuickItem *item)
+{
+    if (!item)
+        return 0;
+
+    const qreal ch = item->implicitHeight();
+    if (!qFuzzyIsNull(ch))
+        return ch;
+
+    const auto contentChildren = item->childItems();
+    if (contentChildren.count() == 1)
+        return contentChildren.first()->implicitHeight();
+
+    return 0;
+}
+
+bool QQuickPanePrivate::updateContentWidth(QQuickItem *item)
+{
+    if (hasContentWidth)
+        return false;
+
+    qreal oldContentWidth = contentWidth;
+    contentWidth = getContentWidth(item);
+    return !qFuzzyCompare(contentWidth, oldContentWidth);
+}
+
+bool QQuickPanePrivate::updateContentHeight(QQuickItem *item)
+{
+    if (hasContentHeight)
+        return false;
+
+    qreal oldContentHeight = contentHeight;
+    contentHeight = getContentHeight(item);
+    return !qFuzzyCompare(contentHeight, oldContentHeight);
+}
+
+void QQuickPanePrivate::updateContentSize(QQuickItem *item)
+{
+    Q_Q(QQuickPane);
+    bool widthChanged = updateContentWidth(item);
+    bool heightChanged = updateContentHeight(item);
+    if (widthChanged)
+        emit q->contentWidthChanged();
+    if (heightChanged)
+        emit q->contentHeightChanged();
+}
+
 QQuickPane::QQuickPane(QQuickItem *parent)
     : QQuickControl(*(new QQuickPanePrivate), parent)
 {
@@ -128,6 +238,12 @@ QQuickPane::QQuickPane(QQuickItem *parent)
 #endif
 }
 
+QQuickPane::~QQuickPane()
+{
+    Q_D(QQuickPane);
+    d->removeImplicitSizeListener(d->contentItem);
+}
+
 QQuickPane::QQuickPane(QQuickPanePrivate &dd, QQuickItem *parent)
     : QQuickControl(dd, parent)
 {
@@ -157,6 +273,7 @@ qreal QQuickPane::contentWidth() const
 void QQuickPane::setContentWidth(qreal width)
 {
     Q_D(QQuickPane);
+    d->hasContentWidth = true;
     if (qFuzzyCompare(d->contentWidth, width))
         return;
 
@@ -164,6 +281,17 @@ void QQuickPane::setContentWidth(qreal width)
     emit contentWidthChanged();
 }
 
+void QQuickPane::resetContentWidth()
+{
+    Q_D(QQuickPane);
+    if (!d->hasContentWidth)
+        return;
+
+    d->hasContentHeight = false;
+    if (d->updateContentWidth(d->contentItem))
+        emit contentWidthChanged();
+}
+
 /*!
     \qmlproperty real QtQuick.Controls::Pane::contentHeight
 
@@ -183,6 +311,7 @@ qreal QQuickPane::contentHeight() const
 void QQuickPane::setContentHeight(qreal height)
 {
     Q_D(QQuickPane);
+    d->hasContentHeight = true;
     if (qFuzzyCompare(d->contentHeight, height))
         return;
 
@@ -190,6 +319,17 @@ void QQuickPane::setContentHeight(qreal height)
     emit contentHeightChanged();
 }
 
+void QQuickPane::resetContentHeight()
+{
+    Q_D(QQuickPane);
+    if (!d->hasContentHeight)
+        return;
+
+    d->hasContentHeight = false;
+    if (d->updateContentHeight(d->contentItem))
+        emit contentHeightChanged();
+}
+
 /*!
     \qmlproperty list<Object> QtQuick.Controls::Pane::contentData
     \default
@@ -237,11 +377,17 @@ QQmlListProperty<QQuickItem> QQuickPane::contentChildren()
 
 void QQuickPane::contentItemChange(QQuickItem *newItem, QQuickItem *oldItem)
 {
+    Q_D(QQuickPane);
     QQuickControl::contentItemChange(newItem, oldItem);
-    if (oldItem)
-        disconnect(oldItem, &QQuickItem::childrenChanged, this, &QQuickPane::contentChildrenChanged);
-    if (newItem)
-        connect(newItem, &QQuickItem::childrenChanged, this, &QQuickPane::contentChildrenChanged);
+    if (oldItem) {
+        d->removeImplicitSizeListener(oldItem);
+        QObjectPrivate::disconnect(oldItem, &QQuickItem::childrenChanged, d, &QQuickPanePrivate::contentChildrenChange);
+    }
+    if (newItem) {
+        d->addImplicitSizeListener(newItem);
+        QObjectPrivate::connect(newItem, &QQuickItem::childrenChanged, d, &QQuickPanePrivate::contentChildrenChange);
+    }
+    d->updateContentSize(newItem);
     emit contentChildrenChanged();
 }
 
diff --git a/src/quicktemplates2/qquickpane_p.h b/src/quicktemplates2/qquickpane_p.h
index 759c59d8..53bf7067 100644
--- a/src/quicktemplates2/qquickpane_p.h
+++ b/src/quicktemplates2/qquickpane_p.h
@@ -58,20 +58,23 @@ class QQuickPanePrivate;
 class Q_QUICKTEMPLATES2_PRIVATE_EXPORT QQuickPane : public QQuickControl
 {
     Q_OBJECT
-    Q_PROPERTY(qreal contentWidth READ contentWidth WRITE setContentWidth NOTIFY contentWidthChanged FINAL)
-    Q_PROPERTY(qreal contentHeight READ contentHeight WRITE setContentHeight NOTIFY contentHeightChanged FINAL)
+    Q_PROPERTY(qreal contentWidth READ contentWidth WRITE setContentWidth RESET resetContentWidth NOTIFY contentWidthChanged FINAL)
+    Q_PROPERTY(qreal contentHeight READ contentHeight WRITE setContentHeight RESET resetContentHeight NOTIFY contentHeightChanged FINAL)
     Q_PROPERTY(QQmlListProperty<QObject> contentData READ contentData FINAL)
     Q_PROPERTY(QQmlListProperty<QQuickItem> contentChildren READ contentChildren NOTIFY contentChildrenChanged FINAL)
     Q_CLASSINFO("DefaultProperty", "contentData")
 
 public:
     explicit QQuickPane(QQuickItem *parent = nullptr);
+    ~QQuickPane();
 
     qreal contentWidth() const;
     void setContentWidth(qreal width);
+    void resetContentWidth();
 
     qreal contentHeight() const;
     void setContentHeight(qreal height);
+    void resetContentHeight();
 
     QQmlListProperty<QObject> contentData();
     QQmlListProperty<QQuickItem> contentChildren();
diff --git a/src/quicktemplates2/qquickpane_p_p.h b/src/quicktemplates2/qquickpane_p_p.h
index 16a07f08..4d9a1747 100644
--- a/src/quicktemplates2/qquickpane_p_p.h
+++ b/src/quicktemplates2/qquickpane_p_p.h
@@ -49,12 +49,13 @@
 //
 
 #include <QtQuickTemplates2/private/qquickcontrol_p_p.h>
+#include <QtQuick/private/qquickitemchangelistener_p.h>
 
 QT_BEGIN_NAMESPACE
 
 class QQuickPane;
 
-class Q_QUICKTEMPLATES2_PRIVATE_EXPORT QQuickPanePrivate : public QQuickControlPrivate
+class Q_QUICKTEMPLATES2_PRIVATE_EXPORT QQuickPanePrivate : public QQuickControlPrivate, public QQuickItemChangeListener
 {
     Q_DECLARE_PUBLIC(QQuickPane)
 
@@ -63,6 +64,21 @@ public:
 
     QQuickItem *getContentItem() override;
 
+    void addImplicitSizeListener(QQuickItem *item);
+    void removeImplicitSizeListener(QQuickItem *item);
+
+    void itemImplicitWidthChanged(QQuickItem *item) override;
+    void itemImplicitHeightChanged(QQuickItem *item) override;
+    void itemDestroyed(QQuickItem *item) override;
+
+    void contentChildrenChange();
+
+    bool updateContentWidth(QQuickItem *item);
+    bool updateContentHeight(QQuickItem *item);
+    void updateContentSize(QQuickItem *item);
+
+    bool hasContentWidth;
+    bool hasContentHeight;
     qreal contentWidth;
     qreal contentHeight;
 };