QRegion: re-add rects() and port setRects() to QSpanHEADdev

In Qt 5, we had QVector<QRect> QRegion::rects(), but it was
deprecated, because just iterating over the QRegion as a container of
QRects was more efficient (QRegion has a SSO for the case of one
rectangle). With QSpan, we can now bring it back with the same
efficiency as iteration, supporting Qt 5 code that never made the move
away from rects() and new code that wishes to make the conversion into
rectangles more explicit. Re-add the Qt 5 tests, which show that the
function is nearly a drop-in replacement for the Qt 5 rects() (QSpan,
at the time of this commit, doesn't have relational operators, yet).

Also add a QSpan overload of setRects(). The old (ptr, n) function
(now obsoleted, but not deprecated) allowed nullptr + n != 0, which
QSpan doesn't accept, so print a warning in that case. Also, QSpan can
hold more than INT_MAX elements on 64-bit platforms, but QRegion's API
was never ported from int to qsizetype, so we need to catch oversized
spans used as inputs, too.

[ChangeLog][QtGui][QRegion] Added QSpan overload of setRects();
re-added Qt5's rects(), but returning QSpan instead of QVector now.

Fixes: QTBUG-124712
Change-Id: I24570c886cbf77abd8d1f4a3f42ae53c892cd9ff
Reviewed-by: Volker Hilsheimer <volker.hilsheimer@qt.io>
Reviewed-by: Edward Welbourne <edward.welbourne@qt.io>

0 files changed, 0 insertions, 0 deletions