Allow the user to choose the UI theme

Mainly useful for those who want dark mode on Windows.

src/frontend/qt_sdl/Config.cpp

@@ -142,6 +142,7 @@ bool MouseHide;
 int MouseHideSeconds;
 
 bool PauseLostFocus;
+std::string UITheme;
 
 int64_t RTCOffset;
 
@@ -344,6 +345,7 @@ ConfigEntry ConfigFile[] =
     {"MouseHide",        1, &MouseHide,        false, false},
     {"MouseHideSeconds", 0, &MouseHideSeconds, 5, false},
     {"PauseLostFocus",   1, &PauseLostFocus,   false, false},
+    {"UITheme",          2, &UITheme, (std::string)"", false},
 
     {"RTCOffset",       3, &RTCOffset,       (int64_t)0, true},
 

src/frontend/qt_sdl/Config.h

@@ -185,6 +185,7 @@ extern bool EnableCheats;
 extern bool MouseHide;
 extern int MouseHideSeconds;
 extern bool PauseLostFocus;
+extern std::string UITheme;
 
 extern int64_t RTCOffset;
 

src/frontend/qt_sdl/InterfaceSettingsDialog.cpp

@@ -16,15 +16,16 @@
     with melonDS. If not, see http://www.gnu.org/licenses/.
 */
 
+#include <QStyleFactory>
 #include "InterfaceSettingsDialog.h"
 #include "ui_InterfaceSettingsDialog.h"
 
 #include "types.h"
 #include "Platform.h"
 #include "Config.h"
+#include "main.h"
 
 InterfaceSettingsDialog* InterfaceSettingsDialog::currentDlg = nullptr;
-
 InterfaceSettingsDialog::InterfaceSettingsDialog(QWidget* parent) : QDialog(parent), ui(new Ui::InterfaceSettingsDialog)
 {
     ui->setupUi(this);
@@ -35,6 +36,18 @@ InterfaceSettingsDialog::InterfaceSettingsDialog(QWidget* parent) : QDialog(pare
     ui->spinMouseHideSeconds->setValue(Config::MouseHideSeconds);
     ui->cbPauseLostFocus->setChecked(Config::PauseLostFocus != 0);
     ui->spinMaxFPS->setValue(Config::MaxFPS);
+
+    const QList<QString> themeKeys = QStyleFactory::keys();
+    const QString currentTheme = qApp->style()->objectName();
+
+    ui->cbxUITheme->addItem("System default", "");
+
+    for (int i = 0; i < themeKeys.length(); i++)
+    {
+        ui->cbxUITheme->addItem(themeKeys[i], themeKeys[i]);
+        if (!Config::UITheme.empty() && themeKeys[i].compare(currentTheme, Qt::CaseInsensitive) == 0)
+            ui->cbxUITheme->setCurrentIndex(i + 1);
+    }
 }
 
 InterfaceSettingsDialog::~InterfaceSettingsDialog()
@@ -63,8 +76,16 @@ void InterfaceSettingsDialog::done(int r)
         Config::PauseLostFocus = ui->cbPauseLostFocus->isChecked() ? 1:0;
         Config::MaxFPS = ui->spinMaxFPS->value();
 
+        QString themeName = ui->cbxUITheme->currentData().toString();
+        Config::UITheme = themeName.toStdString();
+
         Config::Save();
 
+        if (!Config::UITheme.empty())
+            qApp->setStyle(themeName);
+        else
+            qApp->setStyle(*systemThemeName);
+
         emit updateMouseTimer();
     }
 

src/frontend/qt_sdl/InterfaceSettingsDialog.ui

@@ -7,7 +7,7 @@
     <x>0</x>
     <y>0</y>
     <width>337</width>
-    <height>233</height>
+    <height>275</height>
    </rect>
   </property>
   <property name="sizePolicy">
@@ -20,12 +20,29 @@
    <string>Interface settings - melonDS</string>
   </property>
   <layout class="QVBoxLayout" name="verticalLayout" stretch="0,0,0">
-   <item alignment="Qt::AlignTop">
+   <item>
     <widget class="QGroupBox" name="groupBox">
      <property name="title">
-      <string>Main window</string>
+      <string>User interface</string>
      </property>
      <layout class="QVBoxLayout" name="verticalLayout_2">
+      <item>
+       <layout class="QHBoxLayout" name="horizontalLayout_2">
+        <item>
+         <widget class="QLabel" name="label_4">
+          <property name="text">
+           <string>Theme</string>
+          </property>
+          <property name="buddy">
+           <cstring>cbxUITheme</cstring>
+          </property>
+         </widget>
+        </item>
+        <item>
+         <widget class="QComboBox" name="cbxUITheme"/>
+        </item>
+       </layout>
+      </item>
       <item>
        <widget class="QCheckBox" name="cbMouseHide">
         <property name="text">

src/frontend/qt_sdl/main.cpp

@@ -114,6 +114,7 @@ QStringList NdsRomExtensions { ".nds", ".srl", ".dsi", ".ids" };
 QString GbaRomMimeType = "application/x-gba-rom";
 QStringList GbaRomExtensions { ".gba", ".agb" };
 
+QString* systemThemeName;
 
 // This list of supported archive formats is based on libarchive(3) version 3.6.2 (2022-12-09).
 QStringList ArchiveMimeTypes
@@ -292,6 +293,11 @@ int main(int argc, char** argv)
 
     qputenv("QT_SCALE_FACTOR", "1");
 
+#if QT_VERSION_MAJOR == 6 && defined(__WIN32__)
+    // Allow using the system dark theme palette on Windows
+    qputenv("QT_QPA_PLATFORM", "windows:darkmode=2");
+#endif
+
     printf("melonDS " MELONDS_VERSION "\n");
     printf(MELONDS_URL "\n");
 
@@ -360,6 +366,12 @@ int main(int argc, char** argv)
     camManager[0]->setXFlip(Config::Camera[0].XFlip);
     camManager[1]->setXFlip(Config::Camera[1].XFlip);
 
+    systemThemeName = new QString(QApplication::style()->objectName());
+
+    if (!Config::UITheme.empty())
+    {
+        QApplication::setStyle(QString::fromStdString(Config::UITheme));
+    }
 
     Input::JoystickID = Config::JoystickID;
     Input::OpenJoystick();

src/frontend/qt_sdl/main.h

@@ -44,4 +44,6 @@ public:
     bool event(QEvent* event) override;
 };
 
+extern QString* systemThemeName;
+
 #endif // MAIN_H