Qt6.8: Ensure Mixxx uses "windowsvista" Qt style on Windows

src/main.cpp

@@ -3,6 +3,7 @@
 #include <QPixmapCache>
 #include <QString>
 #include <QStringList>
+#include <QStyle>
 #include <QTextCodec>
 #include <QThread>
 #include <QtDebug>
@@ -142,6 +143,26 @@ void adjustScaleFactor(CmdlineArgs* pArgs) {
     }
 }
 
+void applyStyleOverride(CmdlineArgs* pArgs) {
+    if (!pArgs->getStyle().isEmpty()) {
+        qDebug() << "Default style is overwritten by command line argument "
+                    "-style"
+                 << pArgs->getStyle();
+        QApplication::setStyle(pArgs->getStyle());
+        return;
+    }
+    if (qEnvironmentVariableIsSet("QT_STYLE_OVERRIDE")) {
+        QString styleOverride = QString::fromLocal8Bit(qgetenv("QT_STYLE_OVERRIDE"));
+        if (!styleOverride.isEmpty()) {
+            // The environment variable overrides the command line option
+            qDebug() << "Default style is overwritten by env variable "
+                        "QT_STYLE_OVERRIDE"
+                     << styleOverride;
+            QApplication::setStyle(styleOverride);
+        }
+    }
+}
+
 } // anonymous namespace
 
 int main(int argc, char * argv[]) {
@@ -208,6 +229,21 @@ int main(int argc, char * argv[]) {
 
     MixxxApplication app(argc, argv);
 
+#if defined(Q_OS_WIN)
+    // The Mixxx style is based on Qt's WindowsVista style
+    QApplication::setStyle("windowsvista");
+#endif
+
+    applyStyleOverride(&args);
+
+    qInfo() << "Selected Qt style:" << QApplication::style()->objectName();
+
+#if defined(Q_OS_WIN)
+    if (QApplication::style()->objectName() != "windowsvista") {
+        qWarning() << "Qt style for Windows is not set to 'windowsvista'. GUI might look broken!";
+    }
+#endif
+
 #ifdef Q_OS_MACOS
     // TODO: At this point it is too late to provide the same settings path to all components
     // and too early to log errors and give users advises in their system language.

src/util/cmdlineargs.cpp

@@ -350,6 +350,15 @@ bool CmdlineArgs::parse(const QStringList& arguments, CmdlineArgs::ParseMode mod
     parser.addOption(debugAssertBreak);
     parser.addOption(debugAssertBreakDeprecated);
 
+    const QCommandLineOption styleOption(QStringLiteral("style"),
+            forUserFeedback
+                    ? QCoreApplication::translate("CmdlineArgs",
+                              "Sets the application GUI style. Possible values "
+                              "depend on your system configuration.")
+                    : QString(),
+            QStringLiteral("style"));
+    parser.addOption(styleOption);
+
     const QCommandLineOption helpOption = parser.addHelpOption();
     const QCommandLineOption versionOption = parser.addVersionOption();
 
@@ -489,5 +498,9 @@ bool CmdlineArgs::parse(const QStringList& arguments, CmdlineArgs::ParseMode mod
         fputs("Unknown argument for for color.\n", stdout);
     }
 
+    if (parser.isSet(styleOption)) {
+        m_styleName = parser.value(styleOption);
+    }
+
     return true;
 }

src/util/cmdlineargs.h

@@ -71,6 +71,10 @@ class CmdlineArgs final {
     const QString& getResourcePath() const { return m_resourcePath; }
     const QString& getTimelinePath() const { return m_timelinePath; }
 
+    const QString& getStyle() const {
+        return m_styleName;
+    }
+
     void setScaleFactor(double scaleFactor) {
         m_scaleFactor = scaleFactor;
     }
@@ -110,4 +114,5 @@ class CmdlineArgs final {
     QString m_settingsPath;
     QString m_resourcePath;
     QString m_timelinePath;
+    QString m_styleName;
 };