Update.

Signed-off-by: Yuhang Zhao <2546789017@qq.com>

examples/QMainWindow/TitleBar.ui

@@ -11,11 +11,7 @@
    </rect>
   </property>
   <property name="styleSheet">
-   <string notr="true">#TitleBar {
-  border-top: 1px solid rgb(255, 255, 255);
-}
-
-#iconButton, #minimizeButton, #maximizeButton, #closeButton {
+   <string notr="true">#iconButton, #minimizeButton, #maximizeButton, #closeButton {
   background-color: transparent;
   border-radius: 0px;
 }

examples/QMainWindow/main.cpp

@@ -25,6 +25,7 @@
 #include "ui_MainWindow.h"
 #include "ui_TitleBar.h"
 #include <QApplication>
+#include <QStyleOption>
 #include <QWidget>
 #ifdef Q_OS_WINDOWS
 #include "../../winnativeeventfilter.h"
@@ -35,10 +36,22 @@
 int main(int argc, char *argv[])
 {
     QCoreApplication::setAttribute(Qt::AA_DontCreateNativeWidgetSiblings);
+    // High DPI scaling is enabled by default from Qt 6
 #if (QT_VERSION < QT_VERSION_CHECK(6, 0, 0))
+    // Windows: we are using the manifest file to get maximum compatibility
+    // because some APIs are not supprted on old systems such as Windows 7
+    // and Windows 8. And once we have set the DPI awareness level in the
+    // manifest file, any attemptation to try to change it through API will
+    // fail. In other words, Qt won't be able to enable or disable high DPI
+    // scaling or change the DPI awareness level once we have set it in the
+    // manifest file. So the following two lines are uesless actually (However,
+    // they are still useful on other platforms).
     QGuiApplication::setAttribute(Qt::AA_EnableHighDpiScaling);
     QGuiApplication::setAttribute(Qt::AA_UseHighDpiPixmaps);
 #if (QT_VERSION >= QT_VERSION_CHECK(5, 14, 0))
+    // Don't round the scale factor.
+    // This will break QWidget applications because they can't render correctly.
+    // Qt Quick applications won't have this issue.
     QGuiApplication::setHighDpiScaleFactorRoundingPolicy(
         Qt::HighDpiScaleFactorRoundingPolicy::PassThrough);
 #endif
@@ -62,9 +75,6 @@ int main(int argc, char *argv[])
     titleBarWidget.horizontalLayout->insertWidget(1, menuBar);
     menuBar->setMaximumHeight(20);
 
-    titleBarWidget.iconButton->setIcon(mainWindow->windowIcon());
-    titleBarWidget.titleLabel->setText(mainWindow->windowTitle());
-
     mainWindow->setMenuWidget(widget);
 
     QObject::connect(mainWindow,
@@ -95,6 +105,12 @@ int main(int argc, char *argv[])
                          }
                      });
 
+    QStyleOption option;
+    option.initFrom(mainWindow);
+    const QIcon icon = mainWindow->style()->standardIcon(QStyle::SP_ComputerIcon, &option);
+    mainWindow->setWindowIcon(icon);
+    mainWindow->setWindowTitle(QObject::tr("Hello, World!"));
+
 #ifdef Q_OS_WINDOWS
     WinNativeEventFilter::addFramelessWindow(mainWindow);
     const auto data = WinNativeEventFilter::windowData(mainWindow);

winnativeeventfilter.cpp

@@ -184,7 +184,7 @@ bool isWin10OrGreater(const int ver)
 
 bool shouldHaveWindowFrame()
 {
-#if 1
+#if 0
 #if (QT_VERSION >= QT_VERSION_CHECK(5, 9, 0))
     return QOperatingSystemVersion::current() >= QOperatingSystemVersion::Windows10;
 #else