Teach QPlatformWindow about safe area margins and implement for iOS

The safe area margins of a window represent the area that is safe to
place content within, without intersecting areas of the screen where
system UI is placed, or where a screen bezel may cover the content.

QWidget will incorporate the safe area margins into its contents margins,
so that they are are never smaller than the safe area margins. This can be
disabled by unsetting the Qt::WA_ContentsMarginsRespectsSafeArea widget
attribute, which is set by default.

QLayouts will automatically use the contents area of a widget for their
layout, unless the Qt::WA_LayoutOnEntireRect attribute has been set. This
can be used, along with a contents margin of 0 on the actual layout,
to allow e.g. a background image to underlay the status bar and other
system areas on an iOS device, while still allowing child widgets of
that background to be inset based on the safe area.

[ChangeLog][iOS/tvOS] Qt will now take the safe area margins of the
device into account when computing layouts for QtWidgets.

Change-Id: Ife3827ab663f0625c1451e75b14fb8eeffb00754
Reviewed-by: Richard Moe Gustavsen <richard.gustavsen@qt.io>

1 files changed, 3 insertions, 0 deletions

diff --git a/src/widgets/kernel/qwidget_p.h b/src/widgets/kernel/qwidget_p.h
index a24d13e0e1..0c012d1932 100644
--- a/src/widgets/kernel/qwidget_p.h
+++ b/src/widgets/kernel/qwidget_p.h
@@ -513,6 +513,9 @@ public:
     void setLayoutItemMargins(int left, int top, int right, int bottom);
     void setLayoutItemMargins(QStyle::SubElement element, const QStyleOption *opt = 0);
 
+    void updateContentsRect();
+    QMargins safeAreaMargins() const;
+
     // aboutToDestroy() is called just before the contents of
     // QWidget::destroy() is executed. It's used to signal QWidget
     // sub-classes that their internals are about to be released.