QPageLayout: do not calculate an invalid margin

A default constructed QPageLayout has an invalid QPageSize. When
asking for its size, an invalid QSize is returned (-1, -1). This
size is then used to calculate the maximum margins the page layout
can have, resulting in negative margins.

I'm not sure if that makes sense for QPageLayout (in principle, a
negative margin is acceptable, meaning to "grow" the size), but then
this margin is passed as an upper bound to a series of qBound calls in
QPageLayoutPrivate::clampMargins.

To fix this, change the calculations of the maximum margins by using
a lower bound of 0.

Change-Id: I429104acfb2296d9eb1ee54c113e9d7e22d9b6ab
Reviewed-by: Volker Hilsheimer <volker.hilsheimer@qt.io>

1 files changed, 4 insertions, 4 deletions

diff --git a/src/gui/painting/qpagelayout.cpp b/src/gui/painting/qpagelayout.cpp
index def9751aa6..ddd5c9a15b 100644
--- a/src/gui/painting/qpagelayout.cpp
+++ b/src/gui/painting/qpagelayout.cpp
@@ -231,10 +231,10 @@ QMargins QPageLayoutPrivate::marginsPixels(int resolution) const
 void QPageLayoutPrivate::setDefaultMargins(const QMarginsF &minMargins)
 {
     m_minMargins = minMargins;
-    m_maxMargins = QMarginsF(m_fullSize.width() - m_minMargins.right(),
-                             m_fullSize.height() - m_minMargins.bottom(),
-                             m_fullSize.width() - m_minMargins.left(),
-                             m_fullSize.height() - m_minMargins.top());
+    m_maxMargins = QMarginsF(qMax(m_fullSize.width() - m_minMargins.right(), qreal(0)),
+                             qMax(m_fullSize.height() - m_minMargins.bottom(), qreal(0)),
+                             qMax(m_fullSize.width() - m_minMargins.left(), qreal(0)),
+                             qMax(m_fullSize.height() - m_minMargins.top(), qreal(0)));
     if (m_mode == QPageLayout::StandardMode)
         clampMargins(m_margins);
 }