Call updateHighDpiScaling() on screenAdded()

QHighDpiScaling has two init/update functions:
 - initHighDpiScaling(): called once during QGuiApplication construction
 - updateHighDpiScaling(): called whenever (relevant) screen configuration changes

Currently the calls to updateHighDpiScaling() are made from
multiple places including platform code. Simplify by calling
it from two locations:
	- QWindowSystemInterface::handleScreenAdded()
	- QGuiApplicationPrivate::processScreenLogicalDotsPerInchChange()

Replace comment about early calls to qt_defaultDpi with a
test which calls qt_defaultDpiX/Y with no screens attached.
(Looking at the qt_defaultDpiX() implementation, it is unlikely
that there will be a problem as long as updateHighDpiScaling()
is called before QGuiApplication::primaryScreen() starts returning
a non-null value.)

Change-Id: I447db42894617495843a5cb531a1322b000fed62
Reviewed-by: Tor Arne Vestbø <tor.arne.vestbo@qt.io>

1 files changed, 0 insertions, 1 deletions

diff --git a/src/plugins/platforms/windows/qwindowsscreen.cpp b/src/plugins/platforms/windows/qwindowsscreen.cpp
index 19557bfcd0..2544dd6200 100644
--- a/src/plugins/platforms/windows/qwindowsscreen.cpp
+++ b/src/plugins/platforms/windows/qwindowsscreen.cpp
@@ -641,7 +641,6 @@ bool QWindowsScreenManager::handleScreenChanges()
         if (auto theme = QWindowsTheme::instance()) // QTBUG-85734/Wine
             theme->refreshFonts();
     }
-    QHighDpiScaling::updateHighDpiScaling();
     return true;
 }