From a32147182a6d37413cb767b2f032e8ee04d1a0ce Mon Sep 17 00:00:00 2001
From: Janek Bevendorff <janek@jbev.net>
Date: Tue, 28 Jul 2020 19:43:32 +0200
Subject: [PATCH] Switch to classic if theme set to auto and high contast mode
 is on.

The light and dark theme don't respond to Windows's high contrast
accessibility mode, so when the theme is set to "auto", we
default to "classic" instead of "light".

Fixes #5044
---
 src/gui/Application.cpp               | 5 +++++
 src/gui/osutils/winutils/WinUtils.cpp | 6 ++++++
 src/gui/osutils/winutils/WinUtils.h   | 1 +
 3 files changed, 12 insertions(+)

diff --git a/src/gui/Application.cpp b/src/gui/Application.cpp
index bb6d37b9..3e97639d 100644
--- a/src/gui/Application.cpp
+++ b/src/gui/Application.cpp
@@ -147,6 +147,11 @@ void Application::applyTheme()
     auto appTheme = config()->get(Config::GUI_ApplicationTheme).toString();
     if (appTheme == "auto") {
         appTheme = osUtils->isDarkMode() ? "dark" : "light";
+#ifdef Q_OS_WIN
+        if (winUtils()->isHighContrastMode()) {
+            appTheme = "classic";
+        }
+#endif
     }
 
     if (appTheme == "light") {
diff --git a/src/gui/osutils/winutils/WinUtils.cpp b/src/gui/osutils/winutils/WinUtils.cpp
index 385a9389..61e913c9 100644
--- a/src/gui/osutils/winutils/WinUtils.cpp
+++ b/src/gui/osutils/winutils/WinUtils.cpp
@@ -105,3 +105,9 @@ bool WinUtils::isCapslockEnabled()
 {
     return GetKeyState(VK_CAPITAL) == 1;
 }
+
+bool WinUtils::isHighContrastMode() const
+{
+    QSettings settings(R"(HKEY_CURRENT_USER\Control Panel\Accessibility\HighContrast)", QSettings::NativeFormat);
+    return (settings.value("Flags").toInt() & 1u) != 0;
+}
diff --git a/src/gui/osutils/winutils/WinUtils.h b/src/gui/osutils/winutils/WinUtils.h
index bf49f2c7..c1904027 100644
--- a/src/gui/osutils/winutils/WinUtils.h
+++ b/src/gui/osutils/winutils/WinUtils.h
@@ -36,6 +36,7 @@ public:
     bool isLaunchAtStartupEnabled() const override;
     void setLaunchAtStartup(bool enable) override;
     bool isCapslockEnabled() override;
+    bool isHighContrastMode() const;
 
 protected:
     explicit WinUtils(QObject* parent = nullptr);