QRegion: make iterable

Virtually all code in Qt that inspects a QRegion does
so by calling rects(), which returns a QVector<QRect>.

But rects() has a problem: A QRegion that contains just
one rectangle internally is not represented by a QVector,
and the mere act of calling rects() makes QRegion create
one.

So, expose the fact that QRegion is a container of QRects
to users by providing iterators and begin()/end(), which
can be nothrow, since for the one-rectangle case, instead
of vectorize()ing the region, we just return pointers to
(and one past) the 'extent' rectangle.

As a consequence, the iterator type is just const QRect*,
but I think that whatever containers QRegion may use under
the hood in the future, it will be certainly one that is
layout-compatible with a C array.

No mutable iterators are provided, since QRegion maintains
a running bounding-rect, so a mutable iterator would have
to call into QRegion for every change, which doesn't make
sense.

[ChangeLog][QtGui][QRegion] Is now iterable as a container
of QRects: added {c,}{r,}{begin,end}().

Change-Id: I2fa565fac0c1d26e2c0937604b23763cd4e23604
Reviewed-by: Olivier Goffart (Woboq GmbH) <ogoffart@woboq.com>

1 files changed, 12 insertions, 0 deletions

diff --git a/src/gui/painting/qregion.h b/src/gui/painting/qregion.h
index d66f80fcde..f00b1fd284 100644
--- a/src/gui/painting/qregion.h
+++ b/src/gui/painting/qregion.h
@@ -81,6 +81,18 @@ public:
     bool isEmpty() const;
     bool isNull() const;
 
+    typedef const QRect *const_iterator;
+    typedef std::reverse_iterator<const_iterator> const_reverse_iterator;
+
+    const_iterator begin()  const Q_DECL_NOTHROW;
+    const_iterator cbegin() const Q_DECL_NOTHROW { return begin(); }
+    const_iterator end()    const Q_DECL_NOTHROW;
+    const_iterator cend()   const Q_DECL_NOTHROW { return end(); }
+    const_reverse_iterator rbegin()  const Q_DECL_NOTHROW { return const_reverse_iterator(end()); }
+    const_reverse_iterator crbegin() const Q_DECL_NOTHROW { return rbegin(); }
+    const_reverse_iterator rend()    const Q_DECL_NOTHROW { return const_reverse_iterator(begin()); }
+    const_reverse_iterator crend()   const Q_DECL_NOTHROW { return rend(); }
+
     bool contains(const QPoint &p) const;
     bool contains(const QRect &r) const;