Implement heightForWidth support for QTabWidget and QStackedWidget.

The problem was simply that QTabWidget does not have a layout (it
does manual layouting, and since that the heightForWidth implementation
it inherits from QWidget require that the widget has a layout it will
not work and it always returned -1 for QTabWidget). The solution is then
to reimplement heightForWidth().

Unfortunately the patch has several workarounds for BIC:
1. QWidget::hasHeightForWidth() should really have been virtual. Instead
   we add the virtual QWidgetPrivate::hasHeightForWidth().
   Since this is a workaround/bugfix for QTabWidget we decided to keep
   QWidget::hasHeightForWidth() internal for now.

2. We cannot reimplement a virtual function in QStackedLayout.
   We therefore fix QStackedWidget by subclassing QStackedLayout and
   reimplement the virtual functions in the subclass.

This is not an ideal fix, but improves QTabWidget and QStackedWidget
wrt height for width.

Task-number: QTBUG-7792
Reviewed-by: Paul
Reviewed-by: Olivier

4 files changed, 103 insertions, 15 deletions

diff --git a/src/gui/widgets/qsizegrip.cpp b/src/gui/widgets/qsizegrip.cpp
index c9d613a..b5b611c 100644
--- a/src/gui/widgets/qsizegrip.cpp
+++ b/src/gui/widgets/qsizegrip.cpp
@@ -78,15 +78,6 @@ static QWidget *qt_sizegrip_topLevelWidget(QWidget* w)
     return w;
 }
 
-static inline bool hasHeightForWidth(QWidget *widget)
-{
-    if (!widget)
-        return false;
-    if (QLayout *layout = widget->layout())
-        return layout->hasHeightForWidth();
-    return widget->sizePolicy().hasHeightForWidth();
-}
-
 class QSizeGripPrivate : public QWidgetPrivate
 {
     Q_DECLARE_PUBLIC(QSizeGrip)
@@ -318,7 +309,7 @@ void QSizeGrip::mousePressEvent(QMouseEvent * e)
 #ifdef Q_WS_X11
     // Use a native X11 sizegrip for "real" top-level windows if supported.
     if (tlw->isWindow() && X11->isSupportedByWM(ATOM(_NET_WM_MOVERESIZE))
-        && !tlw->testAttribute(Qt::WA_DontShowOnScreen) && !hasHeightForWidth(tlw)) {
+        && !tlw->testAttribute(Qt::WA_DontShowOnScreen) && !qt_widget_private(tlw)->hasHeightForWidth()) {
         XEvent xev;
         xev.xclient.type = ClientMessage;
         xev.xclient.message_type = ATOM(_NET_WM_MOVERESIZE);
@@ -340,7 +331,7 @@ void QSizeGrip::mousePressEvent(QMouseEvent * e)
     }
 #endif // Q_WS_X11
 #ifdef Q_WS_WIN
-    if (tlw->isWindow() && !tlw->testAttribute(Qt::WA_DontShowOnScreen) && !hasHeightForWidth(tlw)) {
+    if (tlw->isWindow() && !tlw->testAttribute(Qt::WA_DontShowOnScreen) && !qt_widget_private(tlw)->hasHeightForWidth()) {
         uint orientation = 0;
         if (d->atBottom())
             orientation = d->atLeft() ? SZ_SIZEBOTTOMLEFT : SZ_SIZEBOTTOMRIGHT;
@@ -429,12 +420,12 @@ void QSizeGrip::mouseMoveEvent(QMouseEvent * e)
 
 #ifdef Q_WS_X11
     if (tlw->isWindow() && X11->isSupportedByWM(ATOM(_NET_WM_MOVERESIZE))
-        && tlw->isTopLevel() && !tlw->testAttribute(Qt::WA_DontShowOnScreen) && !hasHeightForWidth(tlw))
+        && tlw->isTopLevel() && !tlw->testAttribute(Qt::WA_DontShowOnScreen) && !qt_widget_private(tlw)->hasHeightForWidth())
         return;
 #endif
 #ifdef Q_WS_WIN
     if (tlw->isWindow() && GetSystemMenu(tlw->winId(), FALSE) != 0 && internalWinId()
-        && !tlw->testAttribute(Qt::WA_DontShowOnScreen) && !hasHeightForWidth(tlw)) {
+        && !tlw->testAttribute(Qt::WA_DontShowOnScreen) && !qt_widget_private(tlw)->hasHeightForWidth()) {
         MSG msg;
         while(PeekMessage(&msg, winId(), WM_MOUSEMOVE, WM_MOUSEMOVE, PM_REMOVE));
         return;
diff --git a/src/gui/widgets/qstackedwidget.cpp b/src/gui/widgets/qstackedwidget.cpp
index 2509a21..6c4061c 100644
--- a/src/gui/widgets/qstackedwidget.cpp
+++ b/src/gui/widgets/qstackedwidget.cpp
@@ -49,12 +49,54 @@
 
 QT_BEGIN_NAMESPACE
 
+/**
+   QStackedLayout does not support height for width (simply because it does not reimplement
+   heightForWidth() and hasHeightForWidth()). That is not possible to fix without breaking
+   binary compatibility. (QLayout is subject to multiple inheritance).
+   However, we can fix QStackedWidget by simply using a modified version of QStackedLayout
+   that reimplements the hfw-related functions:
+ */
+class QStackedLayoutHFW : public QStackedLayout 
+{ 
+public: 
+    QStackedLayoutHFW(QWidget *parent = 0) : QStackedLayout(parent) {} 
+    bool hasHeightForWidth() const; 
+    int heightForWidth(int width) const; 
+}; 
+ 
+bool QStackedLayoutHFW::hasHeightForWidth() const 
+{ 
+    const int n = count(); 
+ 
+    for (int i = 0; i < n; ++i) { 
+        if (QLayoutItem *item = itemAt(i)) { 
+            if (item->hasHeightForWidth()) 
+                return true; 
+        } 
+    } 
+    return false; 
+} 
+ 
+int QStackedLayoutHFW::heightForWidth(int width) const 
+{ 
+    const int n = count(); 
+ 
+    int hfw = 0; 
+    for (int i = 0; i < n; ++i) { 
+        if (QLayoutItem *item = itemAt(i)) { 
+            hfw = qMax(hfw, item->heightForWidth(width)); 
+        } 
+    } 
+    return hfw; 
+} 
+ 
+
 class QStackedWidgetPrivate : public QFramePrivate
 {
     Q_DECLARE_PUBLIC(QStackedWidget)
 public:
     QStackedWidgetPrivate():layout(0){}
-    QStackedLayout *layout;
+    QStackedLayoutHFW *layout;
     bool blockChildAdd;
 };
 
@@ -138,7 +180,7 @@ QStackedWidget::QStackedWidget(QWidget *parent)
     : QFrame(*new QStackedWidgetPrivate, parent)
 {
     Q_D(QStackedWidget);
-    d->layout = new QStackedLayout(this);
+    d->layout = new QStackedLayoutHFW(this);
     connect(d->layout, SIGNAL(widgetRemoved(int)), this, SIGNAL(widgetRemoved(int)));
     connect(d->layout, SIGNAL(currentChanged(int)), this, SIGNAL(currentChanged(int)));
 }
diff --git a/src/gui/widgets/qtabwidget.cpp b/src/gui/widgets/qtabwidget.cpp
index 583c112..01e9d40 100644
--- a/src/gui/widgets/qtabwidget.cpp
+++ b/src/gui/widgets/qtabwidget.cpp
@@ -195,6 +195,7 @@ public:
     void _q_removeTab(int);
     void _q_tabMoved(int from, int to);
     void init();
+    bool hasHeightForWidth() const;
 
     QTabBar *tabs;
     QStackedWidget *stack;
@@ -246,6 +247,15 @@ void QTabWidgetPrivate::init()
 
 }
 
+bool QTabWidgetPrivate::hasHeightForWidth() const
+{
+    bool has = size_policy.hasHeightForWidth();
+    if (!has && stack)
+        has = qt_widget_private(stack)->hasHeightForWidth();
+    return has;
+}
+
+
 /*!
     Initialize \a option with the values from this QTabWidget. This method is useful
     for subclasses when they need a QStyleOptionTabWidgetFrame, but don't want to fill
@@ -871,6 +881,50 @@ QSize QTabWidget::minimumSizeHint() const
                     .expandedTo(QApplication::globalStrut());
 }
 
+/*
+    \reimp
+*/
+int QTabWidget::heightForWidth(int width) const
+{
+    Q_D(const QTabWidget);
+    QStyleOptionTabWidgetFrameV2 opt;
+    initStyleOption(&opt);
+    opt.state = QStyle::State_None;
+
+    QSize zero(0,0);
+    const QSize padding = style()->sizeFromContents(QStyle::CT_TabWidget, &opt, zero, this)
+                                  .expandedTo(QApplication::globalStrut());
+
+    QSize lc(0, 0), rc(0, 0);
+    if (d->leftCornerWidget)
+        lc = d->leftCornerWidget->sizeHint();
+    if(d->rightCornerWidget)
+        rc = d->rightCornerWidget->sizeHint();
+    if (!d->dirty) {
+        QTabWidget *that = (QTabWidget*)this;
+        that->setUpLayout(true);
+    }
+    QSize t(d->tabs->sizeHint());
+
+    if(usesScrollButtons())
+        t = t.boundedTo(QSize(200,200));
+    else
+        t = t.boundedTo(QApplication::desktop()->size());
+
+    const bool tabIsHorizontal = (d->pos == North || d->pos == South);
+    const int contentsWidth = width - padding.width();
+    int stackWidth = contentsWidth;
+    if (!tabIsHorizontal)
+        stackWidth -= qMax(t.width(), qMax(lc.width(), rc.width()));
+
+    int stackHeight = d->stack->heightForWidth(stackWidth);
+    QSize s(stackWidth, stackHeight);
+
+    QSize contentSize = basicSize(tabIsHorizontal, lc, rc, s, t);
+    return (contentSize + padding).expandedTo(QApplication::globalStrut()).height();
+}
+
+
 /*!
     \reimp
  */
diff --git a/src/gui/widgets/qtabwidget.h b/src/gui/widgets/qtabwidget.h
index 68200c8..ee50655 100644
--- a/src/gui/widgets/qtabwidget.h
+++ b/src/gui/widgets/qtabwidget.h
@@ -129,6 +129,7 @@ public:
 
     QSize sizeHint() const;
     QSize minimumSizeHint() const;
+    int heightForWidth(int width) const;
 
     void setCornerWidget(QWidget * w, Qt::Corner corner = Qt::TopRightCorner);
     QWidget * cornerWidget(Qt::Corner corner = Qt::TopRightCorner) const;