App: Use 'fusion' style only on fractional dpi on Windows

On 200% on 4k screens there is no reason to use the 'fusion' style since
the 'vista' native one works perfectly fine.

Task-number: QTCREATORBUG-16095
Change-Id: I1ffd02891aa5ef30c0172edd949d63d4270400c4
Reviewed-by: Alessandro Portale <alessandro.portale@qt.io>
Reviewed-by: <github-actions-qt-creator@cristianadam.eu>
Reviewed-by: Cristian Adam <cristian.adam@qt.io>

1 files changed, 5 insertions, 3 deletions

diff --git a/src/app/main.cpp b/src/app/main.cpp
index 4105b4cca0..9851078e72 100644
--- a/src/app/main.cpp
+++ b/src/app/main.cpp
@@ -679,10 +679,12 @@ int main(int argc, char **argv)
     setPixmapCacheLimit();
     loadFonts();
 
-    if (Utils::HostOsInfo::isWindowsHost() && !qFuzzyCompare(qApp->devicePixelRatio(), 1.0)
-        && !hasStyleOption) {
+    // On 100% or 200% scaling we can use the default 'Vista' style on Windows
+    qreal tmp;
+    const bool fractionalDpi = !qFuzzyIsNull(std::modf(qApp->devicePixelRatio(), &tmp));
+    if (Utils::HostOsInfo::isWindowsHost() && fractionalDpi && !hasStyleOption)
         QApplication::setStyle(QLatin1String("fusion"));
-    }
+
     const int threadCount = QThreadPool::globalInstance()->maxThreadCount();
     QThreadPool::globalInstance()->setMaxThreadCount(qMax(4, 2 * threadCount));