From 982b3b20c9c354964309e339659e4418636b4147 Mon Sep 17 00:00:00 2001
From: Kovid Goyal <kovid@kovidgoyal.net>
Date: Wed, 5 Feb 2020 14:12:09 +0530
Subject: [PATCH] Ensure headless QPA plugin uses fusion style

---
 src/calibre/headless/headless_integration.cpp | 32 +++++++++++++++++++
 src/calibre/headless/headless_integration.h   |  5 +--
 2 files changed, 35 insertions(+), 2 deletions(-)

diff --git a/src/calibre/headless/headless_integration.cpp b/src/calibre/headless/headless_integration.cpp
index ce5f07226c..5e8345ab20 100644
--- a/src/calibre/headless/headless_integration.cpp
+++ b/src/calibre/headless/headless_integration.cpp
@@ -20,6 +20,7 @@ class QCoreTextFontEngine;
 #include <QtGui/private/qguiapplication_p.h>
 #include <qpa/qplatformwindow.h>
 #include <qpa/qplatformfontdatabase.h>
+#include <qpa/qplatformtheme.h>
 
 QT_BEGIN_NAMESPACE
 
@@ -128,4 +129,35 @@ HeadlessIntegration *HeadlessIntegration::instance()
     return static_cast<HeadlessIntegration *>(QGuiApplicationPrivate::platformIntegration());
 }
 
+static QString themeName() { return QStringLiteral("headless"); }
+
+QStringList HeadlessIntegration::themeNames() const
+{
+    return QStringList(themeName());
+}
+
+// Restrict the styles to "fusion" to prevent native styles requiring native
+// window handles (eg Windows Vista style) from being used.
+class HeadlessTheme : public QPlatformTheme
+{
+public:
+	HeadlessTheme() {}
+
+	QVariant themeHint(ThemeHint h) const override
+	{
+		switch (h) {
+		case StyleNames:
+			return QVariant(QStringList(QStringLiteral("fusion")));
+		default:
+			break;
+		}
+		return QPlatformTheme::themeHint(h);
+	}
+};
+
+QPlatformTheme *HeadlessIntegration::createPlatformTheme(const QString &name) const
+{
+    return name == themeName() ? new HeadlessTheme() : nullptr;
+}
+
 QT_END_NAMESPACE
diff --git a/src/calibre/headless/headless_integration.h b/src/calibre/headless/headless_integration.h
index dc37a021c6..5d32f363a9 100644
--- a/src/calibre/headless/headless_integration.h
+++ b/src/calibre/headless/headless_integration.h
@@ -42,7 +42,9 @@ public:
     QPlatformWindow *createPlatformWindow(QWindow *window) const;
     QPlatformBackingStore *createPlatformBackingStore(QWindow *window) const;
     QAbstractEventDispatcher *createEventDispatcher() const;
-    QPlatformOpenGLContext *createPlatformOpenGLContext(QOpenGLContext *context) const; 
+    QPlatformOpenGLContext *createPlatformOpenGLContext(QOpenGLContext *context) const;
+	QStringList themeNames() const override;
+	QPlatformTheme *createPlatformTheme(const QString &name) const override;
 
     unsigned options() const { return 0; }
 
@@ -56,4 +58,3 @@ private:
 };
 
 QT_END_NAMESPACE
-