Fixed grabWidget sometimes returning uninitialized memory.

Use a QImage initialized with transparent to prevent any translucent
parts of the widget to end up as garbage, and to ensure that the
resulting QPixmap ends up with an alpha format only when needed.

Task-number: QTBUG-14945
Reviewed-by: Kim

2 files changed, 4 insertions, 3 deletions

diff --git a/src/gui/image/qpixmap.cpp b/src/gui/image/qpixmap.cpp
index 64d8ed2..290c0f0 100644
--- a/src/gui/image/qpixmap.cpp
+++ b/src/gui/image/qpixmap.cpp
@@ -1101,10 +1101,11 @@ QPixmap QPixmap::grabWidget(QWidget * widget, const QRect &rect)
     if (!r.intersects(widget->rect()))
         return QPixmap();
 
-    QPixmap res(r.size());
+    QImage res(r.size(), QImage::Format_ARGB32_Premultiplied);
+    res.fill(0);
     widget->d_func()->render(&res, QPoint(), r, QWidget::DrawWindowBackground
                              | QWidget::DrawChildren | QWidget::IgnoreMask, true);
-    return res;
+    return QPixmap::fromImage(res);
 }
 
 /*!
diff --git a/tests/auto/qpixmap/tst_qpixmap.cpp b/tests/auto/qpixmap/tst_qpixmap.cpp
index fdf8311..a733d56 100644
--- a/tests/auto/qpixmap/tst_qpixmap.cpp
+++ b/tests/auto/qpixmap/tst_qpixmap.cpp
@@ -817,7 +817,7 @@ void tst_QPixmap::grabWidget()
     for (int row = 0; row < image.height(); ++row) {
         QRgb *line = reinterpret_cast<QRgb *>(image.scanLine(row));
         for (int col = 0; col < image.width(); ++col)
-            line[col] = qRgb(rand() & 255, row, col);
+            line[col] = qRgba(rand() & 255, row, col, 127);
     }
 
     QPalette pal = widget.palette();