QStylesheetStyle: don't lose precision when drawing a progress bar

When qreal is float, it cannot represent all values an int can take,
so we may lose precision in the expression

  qreal(a) / b

as opposed to the double result

  double(a) / b

For lack of trying, I do not know of a value where this would change
the resulting 'fillWidth' value, but better be safe than sorry, and
use double instead of qreal arithmetic.

Also, when calculating fillRatio, we were converting values back and
forth between qreal and double. Using double everywhere avoids that.

Found while reviewing integer arithmetic in QProgressBar as part of
the fix for QTBUG-57857.

Change-Id: I054cb11d35e3ecf5bf79b5c8ee39029bd23bcf49
Reviewed-by: David Faure <david.faure@kdab.com>

1 files changed, 2 insertions, 2 deletions

diff --git a/src/widgets/styles/qstylesheetstyle.cpp b/src/widgets/styles/qstylesheetstyle.cpp
index d63c96bf0e..68ee8c22d3 100644
--- a/src/widgets/styles/qstylesheetstyle.cpp
+++ b/src/widgets/styles/qstylesheetstyle.cpp
@@ -3903,8 +3903,8 @@ void QStyleSheetStyle::drawControl(ControlElement ce, const QStyleOption *opt, Q
                 if (inverted)
                     reverse = !reverse;
                 const bool indeterminate = pb->minimum == pb->maximum;
-                qreal fillRatio = indeterminate ? 0.50 : qreal(progress - minimum)/(maximum - minimum);
-                int fillWidth = int(rect.width() * fillRatio);
+                const auto fillRatio = indeterminate ? 0.50 : double(progress - minimum) / (maximum - minimum);
+                const auto fillWidth = static_cast<int>(rect.width() * fillRatio);
                 int chunkWidth = fillWidth;
                 if (subRule.hasContentsSize()) {
                     QSize sz = subRule.size();