QHeaderView - add parameter to control sizeHint precision

Currently Qt looks at 1000 rows when scaling a column.
That can be slow in some situations and too inaccurate in others.

With this patch we leave it up to the user to decide how precise
e.g resizeToContents should be.

Change-Id: I6ef60f9a3bb40fc331ce1a1544fdc77488d20ca3
Reviewed-by: Stephen Kelly <stephen.kelly@kdab.com>

5 files changed, 87 insertions, 9 deletions

diff --git a/src/widgets/itemviews/qheaderview.cpp b/src/widgets/itemviews/qheaderview.cpp
index d95e693126..c9a845fc7b 100644
--- a/src/widgets/itemviews/qheaderview.cpp
+++ b/src/widgets/itemviews/qheaderview.cpp
@@ -1253,7 +1253,7 @@ void QHeaderView::setSectionResizeMode(ResizeMode mode)
     property is set to true. This is the default for the horizontal headers provided
     by QTreeView.
 
-    \sa setStretchLastSection()
+    \sa setStretchLastSection(), resizeContentsPrecision()
 */
 
 void QHeaderView::setSectionResizeMode(int logicalIndex, ResizeMode mode)
@@ -1316,6 +1316,53 @@ QHeaderView::ResizeMode QHeaderView::sectionResizeMode(int logicalIndex) const
     return d->headerSectionResizeMode(visual);
 }
 
+/*!
+   \since 5.2
+   Sets how precise QHeaderView should calculate the size when ResizeToContents is used.
+   A low value will provide a less accurate but fast auto resize while a higher
+   value will provide a more accurate resize that however can be slow.
+
+   The number \a precision specifies how many sections that should be consider
+   when calculating the preferred size.
+
+   The default value is 1000 meaning that a horizontal column with auto-resize will look
+   at maximum 1000 rows on calculating when doing an auto resize.
+
+   Special value 0 means that it will look at only the visible area.
+   Special value -1 will imply looking at all elements.
+
+   This value is used in QTableView::sizeHintForColumn(), QTableView::sizeHintForRow()
+   and QTreeView::sizeHintForColumn(). Reimplementing these functions can make this
+   function not having an effect.
+
+   If \a resizeSectionsNow is set to true (default) it will do adjustment of sections by calling
+   resizeSections().  (regardless if the precision was changed).
+
+    \sa resizeContentsPrecision(), setSectionResizeMode(), resizeSections(), QTableView::sizeHintForColumn(), QTableView::sizeHintForRow(), QTreeView::sizeHintForColumn()
+*/
+
+void QHeaderView::setResizeContentsPrecision(int precision, bool resizeSectionsNow)
+{
+    Q_D(QHeaderView);
+    d->resizeContentsPrecision = precision;
+    if (resizeSectionsNow)
+        resizeSections();
+}
+
+/*!
+  \since 5.2
+  Returns how precise QHeaderView will calculate on ResizeToContents.
+
+  \sa setResizeContentsPrecision(), setSectionResizeMode()
+
+*/
+
+int QHeaderView::resizeContentsPrecision() const
+{
+    Q_D(const QHeaderView);
+    return d->resizeContentsPrecision;
+}
+
 // ### Qt 6 - remove this obsolete function
 /*!
     \obsolete
@@ -3583,6 +3630,8 @@ void QHeaderViewPrivate::write(QDataStream &out) const
     out << int(globalResizeMode);
 
     out << sectionItems;
+    if (out.version() >= QDataStream::Qt_5_2)
+        out << resizeContentsPrecision;
 }
 
 bool QHeaderViewPrivate::read(QDataStream &in)
@@ -3634,6 +3683,10 @@ bool QHeaderViewPrivate::read(QDataStream &in)
     }
     sectionItems = newSectionItems;
     recalcSectionStartPos();
+
+    if (in.version() >= QDataStream::Qt_5_2)
+        in >> resizeContentsPrecision;
+
     return true;
 }
 
diff --git a/src/widgets/itemviews/qheaderview.h b/src/widgets/itemviews/qheaderview.h
index 0b94eedf78..3de3d320bf 100644
--- a/src/widgets/itemviews/qheaderview.h
+++ b/src/widgets/itemviews/qheaderview.h
@@ -133,6 +133,10 @@ public:
     ResizeMode sectionResizeMode(int logicalIndex) const;
     void setSectionResizeMode(ResizeMode mode);
     void setSectionResizeMode(int logicalIndex, ResizeMode mode);
+
+    void setResizeContentsPrecision(int precision, bool resizeNow = true);
+    int  resizeContentsPrecision() const;
+
 #if QT_DEPRECATED_SINCE(5, 0)
     inline QT_DEPRECATED void setResizeMode(ResizeMode mode)
         { setSectionResizeMode(mode); }
diff --git a/src/widgets/itemviews/qheaderview_p.h b/src/widgets/itemviews/qheaderview_p.h
index de9321530c..c56e0d6196 100644
--- a/src/widgets/itemviews/qheaderview_p.h
+++ b/src/widgets/itemviews/qheaderview_p.h
@@ -99,7 +99,8 @@ public:
           sectionIndicatorOffset(0),
           sectionIndicator(0),
           globalResizeMode(QHeaderView::Interactive),
-          sectionStartposRecalc(true)
+          sectionStartposRecalc(true),
+          resizeContentsPrecision(1000)
     {}
 
 
@@ -291,6 +292,7 @@ public:
     QHeaderView::ResizeMode globalResizeMode;
     QList<QPersistentModelIndex> persistentHiddenSections;
     mutable bool sectionStartposRecalc;
+    int resizeContentsPrecision;
     // header sections
 
     struct SectionItem {
diff --git a/src/widgets/itemviews/qtableview.cpp b/src/widgets/itemviews/qtableview.cpp
index d72e19114d..41ecd3b48f 100644
--- a/src/widgets/itemviews/qtableview.cpp
+++ b/src/widgets/itemviews/qtableview.cpp
@@ -2208,7 +2208,7 @@ void QTableView::updateGeometries()
     if a larger row height is required by either the vertical header or
     the item delegate, that width will be used instead.
 
-    \sa QWidget::sizeHint, verticalHeader()
+    \sa QWidget::sizeHint, verticalHeader(), QHeaderView::resizeContentsPrecision()
 */
 int QTableView::sizeHintForRow(int row) const
 {
@@ -2218,7 +2218,8 @@ int QTableView::sizeHintForRow(int row) const
         return -1;
 
     ensurePolished();
-    const int maximumProcessCols = 1000; // To avoid this to take forever.
+    const int maximumProcessCols = d->verticalHeader->resizeContentsPrecision();
+
 
     int left = qMax(0, d->horizontalHeader->visualIndexAt(0));
     int right = d->horizontalHeader->visualIndexAt(d->viewport->width());
@@ -2253,6 +2254,9 @@ int QTableView::sizeHintForRow(int row) const
     int idxLeft = left;
     int idxRight = column - 1;
 
+    if (maximumProcessCols == 0)
+        columnsProcessed = 0; // skip the while loop
+
     while (columnsProcessed != maximumProcessCols && (idxLeft > 0 || idxRight < actualRight)) {
         int logicalIdx  = -1;
 
@@ -2306,7 +2310,7 @@ int QTableView::sizeHintForRow(int row) const
     required by either the horizontal header or the item delegate, the larger
     width will be used instead.
 
-    \sa QWidget::sizeHint, horizontalHeader()
+    \sa QWidget::sizeHint, horizontalHeader(), QHeaderView::resizeContentsPrecision()
 */
 int QTableView::sizeHintForColumn(int column) const
 {
@@ -2316,7 +2320,7 @@ int QTableView::sizeHintForColumn(int column) const
         return -1;
 
     ensurePolished();
-    const int maximumProcessRows = 1000; // To avoid this to take forever.
+    const int maximumProcessRows = d->horizontalHeader->resizeContentsPrecision();
 
     int top = qMax(0, d->verticalHeader->visualIndexAt(0));
     int bottom = d->verticalHeader->visualIndexAt(d->viewport->height());
@@ -2345,6 +2349,9 @@ int QTableView::sizeHintForColumn(int column) const
     int idxTop = top;
     int idxBottom = row - 1;
 
+    if (maximumProcessRows == 0)
+        rowsProcessed = 0;  // skip the while loop
+
     while (rowsProcessed != maximumProcessRows && (idxTop > 0 || idxBottom < actualBottom)) {
         int logicalIdx  = -1;
 
@@ -3038,6 +3045,8 @@ void QTableView::showColumn(int column)
 /*!
     Resizes the given \a row based on the size hints of the delegate
     used to render each item in the row.
+
+    \sa resizeRowsToContents(), sizeHintForRow(), QHeaderView::resizeContentsPrecision()
 */
 void QTableView::resizeRowToContents(int row)
 {
@@ -3050,6 +3059,8 @@ void QTableView::resizeRowToContents(int row)
 /*!
     Resizes all rows based on the size hints of the delegate
     used to render each item in the rows.
+
+    \sa resizeRowToContents(), sizeHintForRow(), QHeaderView::resizeContentsPrecision()
 */
 void QTableView::resizeRowsToContents()
 {
@@ -3063,6 +3074,8 @@ void QTableView::resizeRowsToContents()
 
     \note Only visible columns will be resized. Reimplement sizeHintForColumn()
     to resize hidden columns as well.
+
+    \sa resizeColumnsToContents(), sizeHintForColumn(), QHeaderView::resizeContentsPrecision()
 */
 void QTableView::resizeColumnToContents(int column)
 {
@@ -3075,6 +3088,8 @@ void QTableView::resizeColumnToContents(int column)
 /*!
     Resizes all columns based on the size hints of the delegate
     used to render each item in the columns.
+
+    \sa resizeColumnToContents(), sizeHintForColumn(), QHeaderView::resizeContentsPrecision()
 */
 void QTableView::resizeColumnsToContents()
 {
diff --git a/src/widgets/itemviews/qtreeview.cpp b/src/widgets/itemviews/qtreeview.cpp
index 21a408d6f1..38f0aa6a9e 100644
--- a/src/widgets/itemviews/qtreeview.cpp
+++ b/src/widgets/itemviews/qtreeview.cpp
@@ -2565,7 +2565,7 @@ void QTreeView::columnCountChanged(int oldCount, int newCount)
 /*!
   Resizes the \a column given to the size of its contents.
 
-  \sa columnWidth(), setColumnWidth()
+  \sa columnWidth(), setColumnWidth(), sizeHintForColumn(), QHeaderView::resizeContentsPrecision()
 */
 void QTreeView::resizeColumnToContents(int column)
 {
@@ -2801,7 +2801,7 @@ void QTreeView::updateGeometries()
   if a larger column width is required by either the view's header or
   the item delegate, that width will be used instead.
 
-  \sa QWidget::sizeHint, header()
+  \sa QWidget::sizeHint, header(), QHeaderView::resizeContentsPrecision()
 */
 int QTreeView::sizeHintForColumn(int column) const
 {
@@ -2814,7 +2814,7 @@ int QTreeView::sizeHintForColumn(int column) const
     QStyleOptionViewItem option = d->viewOptions();
     const QVector<QTreeViewItem> viewItems = d->viewItems;
 
-    const int maximumProcessRows = 1000; // To avoid this to take forever.
+    const int maximumProcessRows = d->header->resizeContentsPrecision(); // To avoid this to take forever.
 
     int offset = 0;
     int start = d->firstVisibleItem(&offset);
@@ -2835,6 +2835,10 @@ int QTreeView::sizeHintForColumn(int column) const
 
     --end;
     int actualBottom = viewItems.size() - 1;
+
+    if (maximumProcessRows == 0)
+        rowsProcessed = 0; // skip the while loop
+
     while (rowsProcessed != maximumProcessRows && (start > 0 || end < actualBottom)) {
         int idx  = -1;