Revert "Revert "Fix (implement!) hfw/wfh in QGridLayoutEngine""

This reverts commit 5bd6f7eb5c7d87c08539b6c2df416990cc417ec7.

This is a revert of the revert.
It is required apply the merge-request 847, which itself revert back
part of this commit but fixing it the (hopefuly) right way

5 files changed, 678 insertions, 17 deletions

diff --git a/src/gui/graphicsview/qgraphicslayoutitem.cpp b/src/gui/graphicsview/qgraphicslayoutitem.cpp
index ad4b2b5..634f68c 100644
--- a/src/gui/graphicsview/qgraphicslayoutitem.cpp
+++ b/src/gui/graphicsview/qgraphicslayoutitem.cpp
@@ -48,6 +48,7 @@
 #include "qgraphicslayoutitem.h"
 #include "qgraphicslayoutitem_p.h"
 #include "qwidget.h"
+#include "qgraphicswidget.h"
 
 #include <QtDebug>
 
@@ -139,9 +140,11 @@ QSizeF *QGraphicsLayoutItemPrivate::effectiveSizeHints(const QSizeF &constraint)
     if (!sizeHintCacheDirty && cachedConstraint == constraint)
         return cachedSizeHints;
 
+    const bool hasConstraint = constraint.width() >= 0 || constraint.height() >= 0;
+
     for (int i = 0; i < Qt::NSizeHints; ++i) {
         cachedSizeHints[i] = constraint;
-        if (userSizeHints)
+        if (userSizeHints && !hasConstraint)
             combineSize(cachedSizeHints[i], userSizeHints[i]);
     }
 
@@ -259,6 +262,52 @@ void QGraphicsLayoutItemPrivate::setSizeComponent(
     q->updateGeometry();
 }
 
+
+bool QGraphicsLayoutItemPrivate::hasHeightForWidth() const
+{
+    Q_Q(const QGraphicsLayoutItem);
+    if (isLayout) {
+        const QGraphicsLayout *l = static_cast<const QGraphicsLayout *>(q);
+        for (int i = l->count() - 1; i >= 0; --i) {
+            if (QGraphicsLayoutItemPrivate::get(l->itemAt(i))->hasHeightForWidth())
+                return true;
+        }
+    } else if (QGraphicsItem *item = q->graphicsItem()) {
+        if (item->isWidget()) {
+            QGraphicsWidget *w = static_cast<QGraphicsWidget *>(item);
+            if (w->layout()) {
+                return QGraphicsLayoutItemPrivate::get(w->layout())->hasHeightForWidth();
+            }
+        }
+    }
+    return q->sizePolicy().hasHeightForWidth();
+}
+
+bool QGraphicsLayoutItemPrivate::hasWidthForHeight() const
+{
+    // enable this code when we add QSizePolicy::hasWidthForHeight() (For 4.8)
+#if 1
+    return false;
+#else
+    Q_Q(const QGraphicsLayoutItem);
+    if (isLayout) {
+        const QGraphicsLayout *l = static_cast<const QGraphicsLayout *>(q);
+        for (int i = l->count() - 1; i >= 0; --i) {
+            if (QGraphicsLayoutItemPrivate::get(l->itemAt(i))->hasWidthForHeight())
+                return true;
+        }
+    } else if (QGraphicsItem *item = q->graphicsItem()) {
+        if (item->isWidget()) {
+            QGraphicsWidget *w = static_cast<QGraphicsWidget *>(item);
+            if (w->layout()) {
+                return QGraphicsLayoutItemPrivate::get(w->layout())->hasWidthForHeight();
+            }
+        }
+    }
+    return q->sizePolicy().hasWidthForHeight();
+#endif
+}
+
 /*!
     \class QGraphicsLayoutItem
     \brief The QGraphicsLayoutItem class can be inherited to allow your custom
diff --git a/src/gui/graphicsview/qgraphicslayoutitem_p.h b/src/gui/graphicsview/qgraphicslayoutitem_p.h
index 15cc7a5..b752e03 100644
--- a/src/gui/graphicsview/qgraphicslayoutitem_p.h
+++ b/src/gui/graphicsview/qgraphicslayoutitem_p.h
@@ -65,6 +65,9 @@ class Q_AUTOTEST_EXPORT QGraphicsLayoutItemPrivate
 public:
     virtual ~QGraphicsLayoutItemPrivate();
     QGraphicsLayoutItemPrivate(QGraphicsLayoutItem *parent, bool isLayout);
+    static QGraphicsLayoutItemPrivate *get(QGraphicsLayoutItem *q) { return q->d_func();}
+    static const QGraphicsLayoutItemPrivate *get(const QGraphicsLayoutItem *q) { return q->d_func();}
+
     void init();
     QSizeF *effectiveSizeHints(const QSizeF &constraint) const;
     QGraphicsItem *parentItem() const;
@@ -73,6 +76,9 @@ public:
     enum SizeComponent { Width, Height };
     void setSizeComponent(Qt::SizeHint which, SizeComponent component, qreal value);
 
+    bool hasHeightForWidth() const;
+    bool hasWidthForHeight() const;
+
     QSizePolicy sizePolicy;
     QGraphicsLayoutItem *parent;
 
diff --git a/src/gui/graphicsview/qgridlayoutengine.cpp b/src/gui/graphicsview/qgridlayoutengine.cpp
index ae5bf90..1e3addc 100644
--- a/src/gui/graphicsview/qgridlayoutengine.cpp
+++ b/src/gui/graphicsview/qgridlayoutengine.cpp
@@ -545,6 +545,24 @@ QSizePolicy::Policy QGridLayoutItem::sizePolicy(Qt::Orientation orientation) con
                                            : sizePolicy.verticalPolicy();
 }
 
+/*
+  returns true if the size policy returns true for either hasHeightForWidth()
+  or hasWidthForHeight()
+ */
+bool QGridLayoutItem::hasDynamicConstraint() const
+{
+    return QGraphicsLayoutItemPrivate::get(q_layoutItem)->hasHeightForWidth()
+        || QGraphicsLayoutItemPrivate::get(q_layoutItem)->hasWidthForHeight();
+}
+
+Qt::Orientation QGridLayoutItem::dynamicConstraintOrientation() const
+{
+    if (QGraphicsLayoutItemPrivate::get(q_layoutItem)->hasHeightForWidth())
+        return Qt::Vertical;
+    else //if (QGraphicsLayoutItemPrivate::get(q_layoutItem)->hasWidthForHeight())
+        return Qt::Horizontal;
+}
+
 QSizePolicy::ControlTypes QGridLayoutItem::controlTypes(LayoutSide /* side */) const
 {
     return q_layoutItem->sizePolicy().controlType();
@@ -613,7 +631,14 @@ QRectF QGridLayoutItem::geometryWithin(qreal x, qreal y, qreal width, qreal heig
         qreal cellWidth = width;
         qreal cellHeight = height;
 
-        QSizeF size = effectiveMaxSize().boundedTo(QSizeF(cellWidth, cellHeight));
+        QSize constraint;
+        if (hasDynamicConstraint()) {
+            if (dynamicConstraintOrientation() == Qt::Vertical)
+                constraint.setWidth(cellWidth);
+            else
+                constraint.setHeight(cellHeight);
+        }
+        QSizeF size = effectiveMaxSize(constraint).boundedTo(QSizeF(cellWidth, cellHeight));
         width = size.width();
         height = size.height();
 
@@ -675,13 +700,13 @@ void QGridLayoutItem::insertOrRemoveRows(int row, int delta, Qt::Orientation ori
     Note that effectiveSizeHint does not take sizePolicy into consideration,
     (since it only evaluates the hints, as the name implies)
 */
-QSizeF QGridLayoutItem::effectiveMaxSize() const
+QSizeF QGridLayoutItem::effectiveMaxSize(const QSizeF &constraint) const
 {
-    QSizeF size;
+    QSizeF size = constraint;
     bool vGrow = (sizePolicy(Qt::Vertical) & QSizePolicy::GrowFlag) == QSizePolicy::GrowFlag;
     bool hGrow = (sizePolicy(Qt::Horizontal) & QSizePolicy::GrowFlag) == QSizePolicy::GrowFlag;
     if (!vGrow || !hGrow) {
-        QSizeF pref = layoutItem()->effectiveSizeHint(Qt::PreferredSize);
+        QSizeF pref = layoutItem()->effectiveSizeHint(Qt::PreferredSize, constraint);
         if (!vGrow)
             size.setHeight(pref.height());
         if (!hGrow)
@@ -689,7 +714,7 @@ QSizeF QGridLayoutItem::effectiveMaxSize() const
     }
 
     if (!size.isValid()) {
-        QSizeF maxSize = layoutItem()->effectiveSizeHint(Qt::MaximumSize);
+        QSizeF maxSize = layoutItem()->effectiveSizeHint(Qt::MaximumSize, constraint);
         if (size.width() == -1)
             size.setWidth(maxSize.width());
         if (size.height() == -1)
@@ -1010,6 +1035,7 @@ void QGridLayoutEngine::invalidate()
     q_cachedEffectiveLastRows[Ver] = -1;
     q_cachedDataForStyleInfo.invalidate();
     q_cachedSize = QSizeF();
+    q_cachedConstraintOrientation = UnknownConstraint;
 }
 
 static void visualRect(QRectF *geom, Qt::LayoutDirection dir, const QRectF &contentsRect)
@@ -1074,10 +1100,13 @@ QRectF QGridLayoutEngine::cellRect(const QLayoutStyleInfo &styleInfo,
 }
 
 QSizeF QGridLayoutEngine::sizeHint(const QLayoutStyleInfo &styleInfo, Qt::SizeHint which,
-                                   const QSizeF & /* constraint */) const
+                                   const QSizeF &constraint) const
 {
     ensureColumnAndRowData(styleInfo);
 
+    if (hasDynamicConstraint())
+        return dynamicallyConstrainedSizeHint(which, constraint);
+
     switch (which) {
     case Qt::MinimumSize:
         return QSizeF(q_totalBoxes[Hor].q_minimumSize, q_totalBoxes[Ver].q_minimumSize);
@@ -1375,7 +1404,11 @@ void QGridLayoutEngine::fillRowData(QGridLayoutRowData *rowData, const QLayoutSt
                         box = &multiCell.q_box;
                         multiCell.q_stretch = itemStretch;
                     }
-                    box->combine(item->box(orientation));
+                    // Items with constraints are not included in the orientation that
+                    // they are constrained (since it depends on the hfw/constraint function).
+                    // They must be combined at a later stage.
+                    if (!item->hasDynamicConstraint() || orientation != item->dynamicConstraintOrientation())
+                        box->combine(item->box(orientation));
 
                     if (effectiveRowSpan == 1) {
                         QSizePolicy::ControlTypes controls = item->controlTypes(top);
@@ -1532,6 +1565,138 @@ void QGridLayoutEngine::ensureColumnAndRowData(const QLayoutStyleInfo &styleInfo
     q_cachedDataForStyleInfo = styleInfo;
 }
 
+QSizeF QGridLayoutEngine::dynamicallyConstrainedSizeHint(Qt::SizeHint which,
+                                                         const QSizeF &constraint) const
+{
+    Q_ASSERT(hasDynamicConstraint());
+    if (constraint.width() < 0 && constraint.height() < 0) {
+        // Process the hfw / wfh items that we did not process in fillRowData()
+        const Qt::Orientation constraintOrient = constraintOrientation();
+
+        QGridLayoutRowData rowData = constraintOrient == Qt::Vertical ? q_rowData : q_columnData;
+        for (int i = q_items.count() - 1; i >= 0; --i) {
+            QGridLayoutItem *item = q_items.at(i);
+            if (item->hasDynamicConstraint()) {
+                QGridLayoutBox box = item->box(constraintOrient);
+                QGridLayoutBox &rowBox = rowData.boxes[item->firstRow(constraintOrient)];
+                rowBox.combine(box);
+            }
+        }
+
+        QGridLayoutBox totalBoxes[2];
+        if (constraintOrient == Qt::Vertical) {
+            totalBoxes[Hor] = q_columnData.totalBox(0, columnCount());
+            totalBoxes[Ver] = rowData.totalBox(0, rowCount());
+        } else {
+            totalBoxes[Hor] = rowData.totalBox(0, columnCount());
+            totalBoxes[Ver] = q_rowData.totalBox(0, rowCount());
+        }
+        return QSizeF(totalBoxes[Hor].q_sizes(which), totalBoxes[Ver].q_sizes(which));
+    }
+
+
+    Q_ASSERT(constraint.width() >= 0 || constraint.height() >= 0);
+    q_xx.resize(columnCount());
+    q_yy.resize(rowCount());
+    q_widths.resize(columnCount());
+    q_heights.resize(rowCount());
+    q_descents.resize(rowCount());
+
+
+    const Qt::Orientation orientation = constraintOrientation();
+    QGridLayoutRowData *colData;
+    QGridLayoutRowData constrainedRowData;
+    QGridLayoutBox *totalBox;
+    qreal *sizes;
+    qreal *pos;
+    qreal *descents;
+    qreal targetSize;
+    qreal cCount;
+    qreal rCount;
+
+    if (orientation == Qt::Vertical) {
+        // height for width
+        colData = &q_columnData;
+        totalBox = &q_totalBoxes[Hor];
+        sizes = q_widths.data();
+        pos = q_xx.data();
+        descents = 0;
+        targetSize = constraint.width();
+        cCount = columnCount();
+        rCount = rowCount();
+        constrainedRowData = q_rowData;
+    } else {
+        // width for height
+        colData = &q_rowData;
+        totalBox = &q_totalBoxes[Ver];
+        sizes = q_heights.data();
+        pos = q_yy.data();
+        descents = q_descents.data();
+        targetSize = constraint.height();
+        cCount = rowCount();
+        rCount = columnCount();
+        constrainedRowData = q_columnData;
+    }
+    colData->calculateGeometries(0, cCount, targetSize, pos, sizes, descents, *totalBox);
+    for (int i = q_items.count() - 1; i >= 0; --i) {
+        QGridLayoutItem *item = q_items.at(i);
+
+        if (item->hasDynamicConstraint()) {
+            const qreal size = sizes[item->firstColumn(orientation)];
+            QGridLayoutBox box = item->box(orientation, size);
+            QGridLayoutBox &rowBox = constrainedRowData.boxes[item->firstRow(orientation)];
+            rowBox.combine(box);
+        }
+    }
+    const qreal newSize = constrainedRowData.totalBox(0, rCount).q_sizes(which);
+
+    return (orientation == Qt::Vertical) ? QSizeF(targetSize, newSize) : QSizeF(newSize, targetSize);
+}
+
+
+/**
+   returns false if the layout has contradicting constraints (i.e. some items with a horizontal
+   constraint and other items with a vertical constraint)
+ */
+bool QGridLayoutEngine::ensureDynamicConstraint() const
+{
+    if (q_cachedConstraintOrientation == UnknownConstraint) {
+        for (int i = q_items.count() - 1; i >= 0; --i) {
+            QGridLayoutItem *item = q_items.at(i);
+            if (item->hasDynamicConstraint()) {
+                Qt::Orientation itemConstraintOrientation = item->dynamicConstraintOrientation();
+                if (q_cachedConstraintOrientation == UnknownConstraint) {
+                    q_cachedConstraintOrientation = itemConstraintOrientation;
+                } else if (q_cachedConstraintOrientation != itemConstraintOrientation) {
+                    q_cachedConstraintOrientation = UnfeasibleConstraint;
+                    qWarning("QGridLayoutEngine: Unfeasible, cannot mix horizontal and"
+                             " vertical constraint in the same layout");
+                    return false;
+                }
+            }
+        }
+        if (q_cachedConstraintOrientation == UnknownConstraint)
+            q_cachedConstraintOrientation = NoConstraint;
+    }
+    return true;
+}
+
+bool QGridLayoutEngine::hasDynamicConstraint() const
+{
+    if (!ensureDynamicConstraint())
+        return false;
+    return q_cachedConstraintOrientation != NoConstraint;
+}
+
+/*
+ * return value is only valid if hasConstraint() returns true
+ */
+Qt::Orientation QGridLayoutEngine::constraintOrientation() const
+{
+    (void)ensureDynamicConstraint();
+    return (Qt::Orientation)q_cachedConstraintOrientation;
+}
+
 void QGridLayoutEngine::ensureGeometries(const QLayoutStyleInfo &styleInfo,
                                          const QSizeF &size) const
 {
@@ -1544,10 +1709,74 @@ void QGridLayoutEngine::ensureGeometries(const QLayoutStyleInfo &styleInfo,
     q_widths.resize(columnCount());
     q_heights.resize(rowCount());
     q_descents.resize(rowCount());
-    q_columnData.calculateGeometries(0, columnCount(), size.width(), q_xx.data(), q_widths.data(),
-                                     0, q_totalBoxes[Hor]);
-    q_rowData.calculateGeometries(0, rowCount(), size.height(), q_yy.data(), q_heights.data(),
-                                  q_descents.data(), q_totalBoxes[Ver]);
+
+
+    Qt::Orientation orientation = Qt::Vertical;
+    if (hasDynamicConstraint())
+        orientation = constraintOrientation();
+
+    /*
+      In order to do hfw we need to first distribute the columns, then the rows.
+      In order to do wfh we need to first distribute the rows, then the columns.
+
+      If there is no constraint, the order of distributing the rows or columns first is irrelevant.
+      We choose horizontal just to keep the same behaviour as before (however, there shouldn't
+      be any behaviour difference).
+ */
+
+    QGridLayoutRowData *colData;
+    QGridLayoutRowData rowData;
+    qreal *widths;
+    qreal *heights;
+    qreal *xx;
+    qreal *yy;
+    qreal *xdescents = 0;
+    qreal *ydescents = 0;
+    qreal cCount;
+    qreal rCount;
+    QSizeF oSize = size;
+    if (orientation == Qt::Vertical) {
+        // height for width
+        colData = &q_columnData;
+        rowData = q_rowData;
+        widths = q_widths.data();
+        heights = q_heights.data();
+        xx = q_xx.data();
+        yy = q_yy.data();
+        cCount = columnCount();
+        rCount = rowCount();
+        ydescents = q_descents.data();
+    } else {
+        // width for height
+        colData = &q_rowData;
+        rowData = q_columnData;
+        widths = q_heights.data();
+        heights = q_widths.data();
+        xx = q_yy.data();
+        yy = q_xx.data();
+        cCount = rowCount();
+        rCount = columnCount();
+        xdescents = q_descents.data();
+        oSize.transpose();
+    }
+
+    colData->calculateGeometries(0, cCount, oSize.width(), xx, widths,
+                                 xdescents, q_totalBoxes[orientation == Qt::Horizontal]);
+    for (int i = q_items.count() - 1; i >= 0; --i) {
+        QGridLayoutItem *item = q_items.at(i);
+        const int col = item->firstColumn(orientation);
+        const int row = item->firstRow(orientation);
+        if (item->hasDynamicConstraint()) {
+            const qreal sz = widths[col];
+            QGridLayoutBox box = item->box(orientation, sz);
+            rowData.boxes[row].combine(box);
+        }
+    }
+
+    QGridLayoutBox &totalBox = q_totalBoxes[orientation == Qt::Vertical];
+    totalBox = rowData.totalBox(0, rCount);
+    rowData.calculateGeometries(0, rCount, oSize.height(), yy, heights,
+                                 ydescents, totalBox);
 
     q_cachedSize = size;
 }
diff --git a/src/gui/graphicsview/qgridlayoutengine_p.h b/src/gui/graphicsview/qgridlayoutengine_p.h
index 9ac9a8e..580af7e 100644
--- a/src/gui/graphicsview/qgridlayoutengine_p.h
+++ b/src/gui/graphicsview/qgridlayoutengine_p.h
@@ -91,6 +91,14 @@ enum LayoutSide {
     Bottom
 };
 
+enum {
+    NoConstraint,
+    HorizontalConstraint,
+    VerticalConstraint,
+    UnknownConstraint,      // need to update cache
+    UnfeasibleConstraint    // not feasible, it be has some items with Vertical and others with Horizontal constraints
+};
+
 template <typename T>
 class QLayoutParameter
 {
@@ -270,6 +278,10 @@ public:
     inline void setAlignment(Qt::Alignment alignment) { q_alignment = alignment; }
 
     QSizePolicy::Policy sizePolicy(Qt::Orientation orientation) const;
+
+    bool hasDynamicConstraint() const;
+    Qt::Orientation dynamicConstraintOrientation() const;
+
     QSizePolicy::ControlTypes controlTypes(LayoutSide side) const;
     QSizeF sizeHint(Qt::SizeHint which, const QSizeF &constraint = QSizeF()) const;
     QGridLayoutBox box(Qt::Orientation orientation, qreal constraint = -1.0) const;
@@ -280,7 +292,7 @@ public:
     void setGeometry(const QRectF &rect);
     void transpose();
     void insertOrRemoveRows(int row, int delta, Qt::Orientation orientation = Qt::Vertical);
-    QSizeF effectiveMaxSize() const;
+    QSizeF effectiveMaxSize(const QSizeF &constraint) const;
 
 #ifdef QT_DEBUG
     void dump(int indent = 0) const;
@@ -372,6 +384,14 @@ public:
                     int column, int rowSpan, int columnSpan) const;
     QSizeF sizeHint(const QLayoutStyleInfo &styleInfo, Qt::SizeHint which,
                     const QSizeF &constraint) const;
+
+    // heightForWidth / widthForHeight support
+    QSizeF dynamicallyConstrainedSizeHint(Qt::SizeHint which, const QSizeF &constraint) const;
+    bool ensureDynamicConstraint() const;
+    bool hasDynamicConstraint() const;
+    Qt::Orientation constraintOrientation() const;
+
+
     QSizePolicy::ControlTypes controlTypes(LayoutSide side) const;
     void transpose();
     void setVisualDirection(Qt::LayoutDirection direction);
@@ -405,6 +425,7 @@ private:
     // Lazily computed from the above user input
     mutable int q_cachedEffectiveFirstRows[NOrientations];
     mutable int q_cachedEffectiveLastRows[NOrientations];
+    mutable quint8 q_cachedConstraintOrientation : 2;
 
     // Layout item input
     mutable QLayoutStyleInfo q_cachedDataForStyleInfo;
diff --git a/tests/auto/qgraphicsgridlayout/tst_qgraphicsgridlayout.cpp b/tests/auto/qgraphicsgridlayout/tst_qgraphicsgridlayout.cpp
index 5b03767..03c1d5b 100644
--- a/tests/auto/qgraphicsgridlayout/tst_qgraphicsgridlayout.cpp
+++ b/tests/auto/qgraphicsgridlayout/tst_qgraphicsgridlayout.cpp
@@ -107,12 +107,13 @@ private slots:
     void avoidRecursionInInsertItem();
     void styleInfoLeak();
     void task236367_maxSizeHint();
+    void heightForWidth();
 };
 
 class RectWidget : public QGraphicsWidget
 {
 public:
-    RectWidget(QGraphicsItem *parent = 0) : QGraphicsWidget(parent){}
+    RectWidget(QGraphicsItem *parent = 0) : QGraphicsWidget(parent), m_fnConstraint(0) {}
 
     void paint(QPainter *painter, const QStyleOptionGraphicsItem *option, QWidget *widget)
     {
@@ -125,9 +126,12 @@ public:
 
     QSizeF sizeHint(Qt::SizeHint which, const QSizeF &constraint = QSizeF()) const
     {
-        if (m_sizeHints[which].isValid()) {
+        if (constraint.width() < 0 && constraint.height() < 0 && m_sizeHints[which].isValid()) {
             return m_sizeHints[which];
         }
+        if (m_fnConstraint) {
+            return m_fnConstraint(which, constraint);
+        }
         return QGraphicsWidget::sizeHint(which, constraint);
     }
 
@@ -136,7 +140,13 @@ public:
         updateGeometry();
     }
 
+    void setConstraintFunction(QSizeF (*fnConstraint)(Qt::SizeHint, const QSizeF &)) {
+        m_fnConstraint = fnConstraint;
+    }
+
     QSizeF m_sizeHints[Qt::NSizeHints];
+    QSizeF (*m_fnConstraint)(Qt::SizeHint, const QSizeF &);
+
 };
 
 struct ItemDesc
@@ -146,7 +156,8 @@ struct ItemDesc
       m_rowSpan(1),
       m_colSpan(1),
       m_sizePolicy(QSizePolicy(QSizePolicy::Preferred, QSizePolicy::Preferred)),
-      m_align(0)
+      m_align(0),
+      m_fnConstraint(0)
     {
     }
 
@@ -213,8 +224,20 @@ struct ItemDesc
         return (*this);
     }
 
+    ItemDesc &heightForWidth(QSizeF (*fnConstraint)(Qt::SizeHint, const QSizeF &)) {
+        m_fnConstraint = fnConstraint;
+        m_constraintOrientation = Qt::Vertical;
+        return (*this);
+    }
+
     void apply(QGraphicsGridLayout *layout, QGraphicsWidget *item) {
-        item->setSizePolicy(m_sizePolicy);
+        QSizePolicy sp = m_sizePolicy;
+        if (m_fnConstraint) {
+            sp.setHeightForWidth(m_constraintOrientation == Qt::Vertical);
+            //sp.setWidthForHeight(m_constraintOrientation == Qt::Horizontal);
+        }
+
+        item->setSizePolicy(sp);
         for (int i = 0; i < Qt::NSizeHints; ++i) {
             if (!m_sizes[i].isValid())
                 continue;
@@ -233,6 +256,7 @@ struct ItemDesc
                 break;
             }
         }
+
         layout->addItem(item, m_pos.first, m_pos.second, m_rowSpan, m_colSpan);
         layout->setAlignment(item, m_align);
     }
@@ -240,6 +264,7 @@ struct ItemDesc
     void apply(QGraphicsGridLayout *layout, RectWidget *item) {
         for (int i = 0; i < Qt::NSizeHints; ++i)
             item->setSizeHint((Qt::SizeHint)i, m_sizeHints[i]);
+        item->setConstraintFunction(m_fnConstraint);
         apply(layout, static_cast<QGraphicsWidget*>(item));
     }
 
@@ -251,6 +276,9 @@ struct ItemDesc
     QSizeF m_sizeHints[Qt::NSizeHints];
     QSizeF m_sizes[Qt::NSizeHints];
     Qt::Alignment m_align;
+
+    Qt::Orientation m_constraintOrientation;
+    QSizeF (*m_fnConstraint)(Qt::SizeHint, const QSizeF &);
 };
 
 typedef QList<ItemDesc> ItemList;
@@ -2116,6 +2144,17 @@ void tst_QGraphicsGridLayout::alignment2()
     delete widget;
 }
 
+static QSizeF hfw1(Qt::SizeHint, const QSizeF &constraint)
+{
+    QSizeF result(constraint);
+    if (constraint.width() < 0 && constraint.height() < 0) {
+        return QSizeF(50, 400);
+    } else if (constraint.width() >= 0) {
+        result.setHeight(20000./constraint.width());
+    }
+    return result;
+}
+
 void tst_QGraphicsGridLayout::geometries_data()
 {
 
@@ -2145,6 +2184,186 @@ void tst_QGraphicsGridLayout::geometries_data()
                                 << QRectF(0, 0, 60,10) << QRectF(0, 10, 60,10)
                             );
 
+    // change layout height and verify
+    QTest::newRow("hfw-h401") << (ItemList()
+                                    << ItemDesc(0,0)
+                                        .minSize(QSizeF(1,1))
+                                        .preferredSize(QSizeF(50,10))
+                                        .maxSize(QSizeF(100, 100))
+                                    << ItemDesc(0,1)
+                                        .minSize(QSizeF(1,1))
+                                        .preferredSize(QSizeF(50,10))
+                                        .maxSize(QSizeF(100, 100))
+                                    << ItemDesc(1,0)
+                                        .minSize(QSizeF(1,1))
+                                        .preferredSize(QSizeF(50,10))
+                                        .maxSize(QSizeF(100, 100))
+                                    << ItemDesc(1,1)
+                                        .minSize(QSizeF(40,40))
+                                        .preferredSize(QSizeF(50,400))
+                                        .maxSize(QSizeF(500, 500))
+                                        .heightForWidth(hfw1)
+                                )
+                            << QSizeF(100, 401)
+                            << (RectList()
+                                << QRectF(0, 0, 50,  1) << QRectF(50, 0, 50,  1)
+                                << QRectF(0, 1, 50,100) << QRectF(50, 1, 50,400)
+                            );
+
+
+    QTest::newRow("hfw-h408") << (ItemList()
+                                    << ItemDesc(0,0)
+                                        .minSize(QSizeF(1,1))
+                                        .preferredSize(QSizeF(50,10))
+                                        .maxSize(QSizeF(100, 100))
+                                    << ItemDesc(0,1)
+                                        .minSize(QSizeF(1,1))
+                                        .preferredSize(QSizeF(50,10))
+                                        .maxSize(QSizeF(100, 100))
+                                    << ItemDesc(1,0)
+                                        .minSize(QSizeF(1,1))
+                                        .preferredSize(QSizeF(50,10))
+                                        .maxSize(QSizeF(100, 100))
+                                    << ItemDesc(1,1)
+                                        .minSize(QSizeF(40,40))
+                                        .preferredSize(QSizeF(50,400))
+                                        .maxSize(QSizeF(500, 500))
+                                        .heightForWidth(hfw1)
+                                )
+                            << QSizeF(100, 408)
+                            << (RectList()
+                                << QRectF(0, 0, 50,  8) << QRectF(50,  0, 50,  8)
+                                << QRectF(0, 8, 50,100) << QRectF(50,  8, 50,400)
+                            );
+
+    QTest::newRow("hfw-h410") << (ItemList()
+                                    << ItemDesc(0,0)
+                                        .minSize(QSizeF(1,1))
+                                        .preferredSize(QSizeF(50,10))
+                                        .maxSize(QSizeF(100, 100))
+                                    << ItemDesc(0,1)
+                                        .minSize(QSizeF(1,1))
+                                        .preferredSize(QSizeF(50,10))
+                                        .maxSize(QSizeF(100, 100))
+                                    << ItemDesc(1,0)
+                                        .minSize(QSizeF(1,1))
+                                        .preferredSize(QSizeF(50,10))
+                                        .maxSize(QSizeF(100, 100))
+                                    << ItemDesc(1,1)
+                                        .minSize(QSizeF(40,40))
+                                        .preferredSize(QSizeF(50,400))
+                                        .maxSize(QSizeF(500, 500))
+                                        .heightForWidth(hfw1)
+                                )
+                            << QSizeF(100, 410)
+                            << (RectList()
+                                << QRectF(0, 0, 50,10) << QRectF(50, 0, 50,10)
+                                << QRectF(0, 10, 50,100) << QRectF(50, 10, 50,400)
+                            );
+
+    QTest::newRow("hfw-h470") << (ItemList()
+                                    << ItemDesc(0,0)
+                                        .minSize(QSizeF(1,1))
+                                        .preferredSize(QSizeF(50,10))
+                                        .maxSize(QSizeF(100, 100))
+                                    << ItemDesc(0,1)
+                                        .minSize(QSizeF(1,1))
+                                        .preferredSize(QSizeF(50,10))
+                                        .maxSize(QSizeF(100, 100))
+                                    << ItemDesc(1,0)
+                                        .minSize(QSizeF(1,1))
+                                        .preferredSize(QSizeF(50,10))
+                                        .maxSize(QSizeF(100, 100))
+                                    << ItemDesc(1,1)
+                                        .minSize(QSizeF(40,40))
+                                        .preferredSize(QSizeF(50,400))
+                                        .maxSize(QSizeF(500, 500))
+                                        .heightForWidth(hfw1)
+                                )
+                            << QSizeF(100, 470)
+                            << (RectList()
+                                << QRectF(0, 0, 50,70) << QRectF(50, 0, 50,70)
+                                << QRectF(0, 70, 50,100) << QRectF(50, 70, 50,400)
+                            );
+
+
+    // change layout width and verify
+    QTest::newRow("hfw-w100") << (ItemList()
+                                    << ItemDesc(0,0)
+                                        .minSize(QSizeF(1,1))
+                                        .preferredSize(QSizeF(50,10))
+                                        .maxSize(QSizeF(100, 100))
+                                    << ItemDesc(0,1)
+                                        .minSize(QSizeF(1,1))
+                                        .preferredSize(QSizeF(50,10))
+                                        .maxSize(QSizeF(100, 100))
+                                    << ItemDesc(1,0)
+                                        .minSize(QSizeF(1,1))
+                                        .preferredSize(QSizeF(50,10))
+                                        .maxSize(QSizeF(100, 100))
+                                    << ItemDesc(1,1)
+                                        .minSize(QSizeF(40,40))
+                                        .preferredSize(QSizeF(50,400))
+                                        .maxSize(QSizeF(5000, 5000))
+                                        .heightForWidth(hfw1)
+                                )
+                            << QSizeF(100, 401)
+                            << (RectList()
+                                << QRectF( 0, 0,  50,   1) << QRectF( 50,  0,  50,   1)
+                                << QRectF( 0, 1,  50, 100) << QRectF( 50,  1,  50, 400)
+                            );
+
+    QTest::newRow("hfw-w160") << (ItemList()
+                                    << ItemDesc(0,0)
+                                        .minSize(QSizeF(1,1))
+                                        .preferredSize(QSizeF(50,10))
+                                        .maxSize(QSizeF(100, 100))
+                                    << ItemDesc(0,1)
+                                        .minSize(QSizeF(1,1))
+                                        .preferredSize(QSizeF(50,10))
+                                        .maxSize(QSizeF(100, 100))
+                                    << ItemDesc(1,0)
+                                        .minSize(QSizeF(1,1))
+                                        .preferredSize(QSizeF(50,10))
+                                        .maxSize(QSizeF(100, 100))
+                                    << ItemDesc(1,1)
+                                        .minSize(QSizeF(40,40))
+                                        .preferredSize(QSizeF(50,400))
+                                        .maxSize(QSizeF(5000, 5000))
+                                        .heightForWidth(hfw1)
+                                )
+                            << QSizeF(160, 401)
+                            << (RectList()
+                                << QRectF( 0,   0,  80, 100) << QRectF( 80,   0,  80, 100)
+                                << QRectF( 0, 100,  80, 100) << QRectF( 80, 100,  80, 250)
+                            );
+
+
+    QTest::newRow("hfw-w500") << (ItemList()
+                                    << ItemDesc(0,0)
+                                        .minSize(QSizeF(1,1))
+                                        .preferredSize(QSizeF(50,10))
+                                        .maxSize(QSizeF(100, 100))
+                                    << ItemDesc(0,1)
+                                        .minSize(QSizeF(1,1))
+                                        .preferredSize(QSizeF(50,10))
+                                        .maxSize(QSizeF(100, 100))
+                                    << ItemDesc(1,0)
+                                        .minSize(QSizeF(1,1))
+                                        .preferredSize(QSizeF(50,10))
+                                        .maxSize(QSizeF(100, 100))
+                                    << ItemDesc(1,1)
+                                        .minSize(QSizeF(40,40))
+                                        .preferredSize(QSizeF(50,400))
+                                        .maxSize(QSizeF(5000, 5000))
+                                        .heightForWidth(hfw1)
+                                )
+                            << QSizeF(500, 401)
+                            << (RectList()
+                                << QRectF( 0,   0, 100, 100) << QRectF(100,   0, 100, 100)
+                                << QRectF( 0, 100, 100, 100) << QRectF(100, 100, 400,  50)
+                            );
+
 }
 
 void tst_QGraphicsGridLayout::geometries()
@@ -2215,6 +2434,143 @@ void tst_QGraphicsGridLayout::task236367_maxSizeHint()
     QCOMPARE(widget->size(), QSizeF(w, h));
 }
 
+/*
+static qreal hfw(qreal w)
+{
+    if (w == 0)
+        return 20000;
+    return 20000/w;
+}
+*/
+static QSizeF hfw(Qt::SizeHint /*which*/, const QSizeF &constraint)
+{
+    QSizeF result(constraint);
+    const qreal cw = constraint.width();
+    const qreal ch = constraint.height();
+    if (cw < 0 && ch < 0) {
+        return QSizeF(200, 100);
+    } else if (cw >= 0) {
+        result.setHeight(20000./cw);
+    } else if (cw == 0) {
+        result.setHeight(20000);
+    } else if (ch >= 0) {
+        result.setWidth(20000./ch);
+    } else if (ch == 0) {
+        result.setWidth(20000);
+    }
+
+    return result;
+}
+
+static qreal growthFactorBelowPreferredSize(qreal desired, qreal sumAvailable, qreal sumDesired)
+{
+    Q_ASSERT(sumDesired != 0.0);
+    return desired * qPow(sumAvailable / sumDesired, desired / sumDesired);
+}
+
+static void expectedWidth(qreal minSize1, qreal prefSize1,
+                          qreal minSize2, qreal prefSize2,
+                          qreal targetSize, qreal *width1, qreal *width2)
+{
+    qreal sumAvail,factor1,factor2;
+    // stretch behaviour is different below and above preferred size...
+    if (targetSize < prefSize1 + prefSize2) {
+        sumAvail = targetSize - minSize1 - minSize2;
+        const qreal desired1 = prefSize1 - minSize1;
+        const qreal desired2 = prefSize2 - minSize2;
+        const qreal sumDesired = desired1 + desired2;
+        factor1 = growthFactorBelowPreferredSize(desired1, sumAvail, sumDesired);
+        factor2 = growthFactorBelowPreferredSize(desired2, sumAvail, sumDesired);
+        const qreal sumFactors = factor1 + factor2;
+        *width1 = sumAvail*factor1/sumFactors + minSize1;
+        *width2 = sumAvail*factor2/sumFactors + minSize2;
+    } else {
+        sumAvail = targetSize - prefSize1 - prefSize2;
+        factor1 = prefSize1;
+        factor2 = prefSize2;
+        const qreal sumFactors = factor1 + factor2;
+        *width1 = sumAvail*factor1/sumFactors + prefSize1;
+        *width2 = sumAvail*factor2/sumFactors + prefSize2;
+    }
+}
+
+
+bool qFuzzyCompare(const QSizeF &a, const QSizeF &b)
+{
+    return qFuzzyCompare(a.width(), b.width()) && qFuzzyCompare(a.height(), b.height());
+}
+
+void tst_QGraphicsGridLayout::heightForWidth()
+{
+    QGraphicsWidget *widget = new QGraphicsWidget;
+    QGraphicsGridLayout *layout = new QGraphicsGridLayout;
+    widget->setLayout(layout);
+    layout->setContentsMargins(0, 0, 0, 0);
+    layout->setSpacing(0);
+    RectWidget *w00 = new RectWidget;
+    w00->setSizeHint(Qt::MinimumSize, QSizeF(1,1));
+    w00->setSizeHint(Qt::PreferredSize, QSizeF(10,10));
+    w00->setSizeHint(Qt::MaximumSize, QSizeF(100,100));
+    layout->addItem(w00, 0, 0);
+
+    RectWidget *w01 = new RectWidget;
+    w01->setSizeHint(Qt::MinimumSize, QSizeF(1,1));
+    w01->setSizeHint(Qt::PreferredSize, QSizeF(10,10));
+    w01->setSizeHint(Qt::MaximumSize, QSizeF(100,100));
+    layout->addItem(w01, 0, 1);
+
+    RectWidget *w10 = new RectWidget;
+    w10->setSizeHint(Qt::MinimumSize, QSizeF(1,1));
+    w10->setSizeHint(Qt::PreferredSize, QSizeF(10,10));
+    w10->setSizeHint(Qt::MaximumSize, QSizeF(100,100));
+    layout->addItem(w10, 1, 0);
+
+    RectWidget *w11 = new RectWidget;
+    w11->setSizeHint(Qt::MinimumSize, QSizeF(1,1));
+    w11->setSizeHint(Qt::MaximumSize, QSizeF(30000,30000));
+    w11->setConstraintFunction(hfw);
+    QSizePolicy sp(QSizePolicy::Preferred, QSizePolicy::Preferred);
+    sp.setHeightForWidth(true);
+    w11->setSizePolicy(sp);
+    layout->addItem(w11, 1, 1);
+
+    QSizeF prefSize = layout->effectiveSizeHint(Qt::PreferredSize, QSizeF(-1, -1));
+    QCOMPARE(prefSize, QSizeF(10+200, 10+100));
+
+    QCOMPARE(layout->effectiveSizeHint(Qt::MinimumSize, QSizeF(2, -1)), QSizeF(2, 20001));
+    QCOMPARE(layout->effectiveSizeHint(Qt::PreferredSize, QSizeF(2, -1)), QSizeF(2, 20010));
+    QCOMPARE(layout->effectiveSizeHint(Qt::MaximumSize, QSizeF(2, -1)), QSizeF(2, 20100));
+    qreal width1;
+    qreal width2;
+    expectedWidth(1, 10, 1, 200, 20, &width1, &width2);
+    QSizeF expectedSize = hfw(Qt::MinimumSize, QSizeF(width2, -1)) + QSizeF(width1, 1);
+    QCOMPARE(layout->effectiveSizeHint(Qt::MinimumSize, QSizeF(20, -1)), expectedSize);
+    expectedSize.rheight()+=9;
+    QCOMPARE(layout->effectiveSizeHint(Qt::PreferredSize, QSizeF(20, -1)), expectedSize);
+    expectedSize.rheight()+=90;
+    QCOMPARE(layout->effectiveSizeHint(Qt::MaximumSize, QSizeF(20, -1)), expectedSize);
+
+    expectedWidth(1, 10, 1, 200, 300, &width1, &width2);
+    expectedSize = hfw(Qt::MinimumSize, QSizeF(width2, -1)) + QSizeF(width1, 1);
+    QCOMPARE(layout->effectiveSizeHint(Qt::MinimumSize, QSizeF(300, -1)), expectedSize);
+    expectedSize.rheight()+=9;
+    QCOMPARE(layout->effectiveSizeHint(Qt::PreferredSize, QSizeF(300, -1)), expectedSize);
+    // the height of the hfw widget is shorter than the one to the left, which is 100, so
+    // the total height of the last row is 100 (which leaves the layout height to be 200)
+    QCOMPARE(layout->effectiveSizeHint(Qt::MaximumSize, QSizeF(300, -1)), QSizeF(300, 200));
+
+    // the hfw item is shorter than the item to the left
+    expectedWidth(1, 10, 1, 200, 500, &width1, &width2);
+    expectedSize = hfw(Qt::MinimumSize, QSizeF(width2, -1)) + QSizeF(width1, 1);
+    QCOMPARE(layout->effectiveSizeHint(Qt::MinimumSize, QSizeF(500, -1)), expectedSize);
+    expectedSize.rheight()+=9;
+    QCOMPARE(layout->effectiveSizeHint(Qt::PreferredSize, QSizeF(500, -1)), expectedSize);
+    // the height of the hfw widget is shorter than the one to the left, which is 100, so
+    // the total height of the last row is 100 (which leaves the layout height to be 200)
+    QCOMPARE(layout->effectiveSizeHint(Qt::MaximumSize, QSizeF(500, -1)), QSizeF(500, 200));
+
+}
+
 QTEST_MAIN(tst_QGraphicsGridLayout)
 #include "tst_qgraphicsgridlayout.moc"