add support for multiple custom themes

also moved theme related code from Application.cpp to new ui/themes/ThemeManager.cpp, this class should cleanly isolate theme related functions and help avoid code duplication in future theme related additions.
Themes can now be just qss or css files, they won't have color pallette information with them in that case

Signed-off-by: Tayou <tayou@gmx.net>

launcher/Application.cpp

@@ -1,7 +1,10 @@
 // SPDX-License-Identifier: GPL-3.0-only
 /*
- *  PolyMC - Minecraft Launcher
+ *  Prism Launcher
  *  Copyright (C) 2022 Sefa Eyeoglu <contact@scrumplex.net>
+ *  Copyright (C) 2022 Tayou <tayou@gmx.net>
+ *
+ *  PolyMC - Minecraft Launcher
  *  Copyright (C) 2022 Lenny McLennington <lenny@sneed.church>
  *
  *  This program is free software: you can redistribute it and/or modify
@@ -54,12 +57,6 @@
 #include "ui/pages/global/APIPage.h"
 #include "ui/pages/global/CustomCommandsPage.h"
 
-#include "ui/themes/ITheme.h"
-#include "ui/themes/SystemTheme.h"
-#include "ui/themes/DarkTheme.h"
-#include "ui/themes/BrightTheme.h"
-#include "ui/themes/CustomTheme.h"
-
 #ifdef Q_OS_WIN
 #include "ui/WinDarkmode.h"
 #include <versionhelpers.h>
@@ -749,28 +746,11 @@ Application::Application(int &argc, char **argv) : QApplication(argc, argv)
         qDebug() << "<> Instance icons intialized.";
     }
 
-    // Icon themes
+    // Themes
     {
-        // TODO: icon themes and instance icons do not mesh well together. Rearrange and fix discrepancies!
+        m_themeManager = new ThemeManager(m_mainWindow);
-        // set icon theme search path!
-        auto searchPaths = QIcon::themeSearchPaths();
-        searchPaths.append("iconthemes");
-        QIcon::setThemeSearchPaths(searchPaths);
-        qDebug() << "<> Icon themes initialized.";
-    }
 
-    // Initialize widget themes
+        m_themeManager->InitializeThemes();
-    {
-        auto insertTheme = [this](ITheme * theme)
-        {
-            m_themes.insert(std::make_pair(theme->id(), std::unique_ptr<ITheme>(theme)));
-        };
-        auto darkTheme = new DarkTheme();
-        insertTheme(new SystemTheme());
-        insertTheme(darkTheme);
-        insertTheme(new BrightTheme());
-        insertTheme(new CustomTheme(darkTheme, "custom"));
-        qDebug() << "<> Widget themes initialized.";
     }
 
     // initialize and load all instances
@@ -880,6 +860,10 @@ Application::Application(int &argc, char **argv) : QApplication(argc, argv)
     performMainStartupAction();
 }
 
+ThemeManager* Application::getThemeManager() {
+    return Application::m_themeManager;
+}
+
 bool Application::createSetupWizard()
 {
     bool javaRequired = [&]()
@@ -1127,43 +1111,17 @@ std::shared_ptr<JavaInstallList> Application::javalist()
 
 std::vector<ITheme *> Application::getValidApplicationThemes()
 {
-    std::vector<ITheme *> ret;
+    return m_themeManager->getValidApplicationThemes();
-    auto iter = m_themes.cbegin();
-    while (iter != m_themes.cend())
-    {
-        ret.push_back((*iter).second.get());
-        iter++;
-    }
-    return ret;
 }
 
 void Application::setApplicationTheme(const QString& name, bool initial)
 {
-    auto systemPalette = qApp->palette();
+    m_themeManager->setApplicationTheme(name, initial);
-    auto themeIter = m_themes.find(name);
-    if(themeIter != m_themes.end())
-    {
-        auto & theme = (*themeIter).second;
-        theme->apply(initial);
-#ifdef Q_OS_WIN
-        if (m_mainWindow && IsWindows10OrGreater()) {
-            if (QString::compare(theme->id(), "dark") == 0) {
-                    WinDarkmode::setDarkWinTitlebar(m_mainWindow->winId(), true);
-            } else {
-                    WinDarkmode::setDarkWinTitlebar(m_mainWindow->winId(), false);
-            }
-        }
-#endif
-    }
-    else
-    {
-        qWarning() << "Tried to set invalid theme:" << name;
-    }
 }
 
 void Application::setIconTheme(const QString& name)
 {
-    QIcon::setThemeName(name);
+    m_themeManager->setIconTheme(name);
 }
 
 QIcon Application::getThemedIcon(const QString& name)

launcher/Application.h

@@ -1,7 +1,8 @@
 // SPDX-License-Identifier: GPL-3.0-only
 /*
- *  PolyMC - Minecraft Launcher
+ *  Prism Launcher
  *  Copyright (C) 2022 Sefa Eyeoglu <contact@scrumplex.net>
+ *  Copyright (C) 2022 Tayou <tayou@gmx.net>
  *
  *  This program is free software: you can redistribute it and/or modify
  *  it under the terms of the GNU General Public License as published by
@@ -44,6 +45,8 @@
 #include <QUrl>
 #include <updater/GoUpdate.h>
 
+#include "ui/themes/ThemeManager.h"
+
 #include <BaseInstance.h>
 
 #include "minecraft/launch/MinecraftServerTarget.h"
@@ -198,6 +201,8 @@ public:
 
     void ShowGlobalSettings(class QWidget * parent, QString open_page = QString());
 
+    ThemeManager* getThemeManager();
+
 signals:
     void updateAllowedChanged(bool status);
     void globalSettingsAboutToOpen();
@@ -255,9 +260,9 @@ private:
     std::shared_ptr<JavaInstallList> m_javalist;
     std::shared_ptr<TranslationsModel> m_translations;
     std::shared_ptr<GenericPageProvider> m_globalSettingsProvider;
-    std::map<QString, std::unique_ptr<ITheme>> m_themes;
     std::unique_ptr<MCEditTool> m_mcedit;
     QSet<QString> m_features;
+    ThemeManager* m_themeManager;
 
     QMap<QString, std::shared_ptr<BaseProfilerFactory>> m_profilers;
 

launcher/CMakeLists.txt

@@ -650,6 +650,8 @@ SET(LAUNCHER_SOURCES
     ui/themes/ITheme.h
     ui/themes/SystemTheme.cpp
     ui/themes/SystemTheme.h
+    ui/themes/ThemeManager.cpp
+    ui/themes/ThemeManager.h
 
     # Processes
     LaunchController.h

launcher/ui/themes/CustomTheme.cpp

@@ -1,12 +1,49 @@
+// SPDX-License-Identifier: GPL-3.0-only
+/*
+ *  Prism Launcher
+ *  Copyright (C) 2022 Tayou <tayou@gmx.net>
+ *
+ *  This program is free software: you can redistribute it and/or modify
+ *  it under the terms of the GNU General Public License as published by
+ *  the Free Software Foundation, version 3.
+ *
+ *  This program is distributed in the hope that it will be useful,
+ *  but WITHOUT ANY WARRANTY; without even the implied warranty of
+ *  MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ *  GNU General Public License for more details.
+ *
+ *  You should have received a copy of the GNU General Public License
+ *  along with this program.  If not, see <https://www.gnu.org/licenses/>.
+ *
+ * This file incorporates work covered by the following copyright and
+ * permission notice:
+ *
+ *      Copyright 2013-2021 MultiMC Contributors
+ *
+ *      Authors: Andrew Okin
+ *               Peterix
+ *               Orochimarufan <orochimarufan.x3@gmail.com>
+ *
+ *      Licensed under the Apache License, Version 2.0 (the "License");
+ *      you may not use this file except in compliance with the License.
+ *      You may obtain a copy of the License at
+ *
+ *          http://www.apache.org/licenses/LICENSE-2.0
+ *
+ *      Unless required by applicable law or agreed to in writing, software
+ *      distributed under the License is distributed on an "AS IS" BASIS,
+ *      WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ *      See the License for the specific language governing permissions and
+ *      limitations under the License.
+ */
 #include "CustomTheme.h"
-#include <QDir>
 #include <Json.h>
 #include <FileSystem.h>
+#include "ThemeManager.h"
 
 const char * themeFile = "theme.json";
-const char * styleFile = "themeStyle.css";
 
-static bool readThemeJson(const QString &path, QPalette &palette, double &fadeAmount, QColor &fadeColor, QString &name, QString &widgets)
+static bool readThemeJson(const QString &path, QPalette &palette, double &fadeAmount, QColor &fadeColor, QString &name, QString &widgets, QString &qssFilePath, bool &dataIncomplete)
 {
     QFileInfo pathInfo(path);
     if(pathInfo.exists() && pathInfo.isFile())
@@ -15,8 +52,11 @@ static bool readThemeJson(const QString &path, QPalette &palette, double &fadeAm
         {
             auto doc = Json::requireDocument(path, "Theme JSON file");
             const QJsonObject root = doc.object();
+            dataIncomplete = !root.contains("qssFilePath");
             name = Json::requireString(root, "name", "Theme name");
             widgets = Json::requireString(root, "widgets", "Qt widget theme");
+            qssFilePath = Json::ensureString(root, "qssFilePath", "themeStyle.css");
+            //auto colorFileList = Json::ensureArray(root, "colorFiles");
             auto colorsRoot = Json::requireObject(root, "colors", "colors object");
             auto readColor = [&](QString colorName) -> QColor
             {
@@ -26,7 +66,7 @@ static bool readThemeJson(const QString &path, QPalette &palette, double &fadeAm
                     QColor color(colorValue);
                     if(!color.isValid())
                     {
-                        qWarning() << "Color value" << colorValue << "for" << colorName << "was not recognized.";
+                        themeWarningLog << "Color value" << colorValue << "for" << colorName << "was not recognized.";
                         return QColor();
                     }
                     return color;
@@ -42,7 +82,7 @@ static bool readThemeJson(const QString &path, QPalette &palette, double &fadeAm
                 }
                 else
                 {
-                    qDebug() << "Color value for" << colorName << "was not present.";
+                    themeDebugLog << "Color value for" << colorName << "was not present.";
                 }
             };
 
@@ -68,23 +108,24 @@ static bool readThemeJson(const QString &path, QPalette &palette, double &fadeAm
         }
         catch (const Exception &e)
         {
-            qWarning() << "Couldn't load theme json: " << e.cause();
+            themeWarningLog << "Couldn't load theme json: " << e.cause();
             return false;
         }
     }
     else
     {
-        qDebug() << "No theme json present.";
+        themeDebugLog << "No theme json present.";
         return false;
     }
     return true;
 }
 
-static bool writeThemeJson(const QString &path, const QPalette &palette, double fadeAmount, QColor fadeColor, QString name, QString widgets)
+static bool writeThemeJson(const QString &path, const QPalette &palette, double fadeAmount, QColor fadeColor, QString name, QString widgets, QString qssFilePath)
 {
     QJsonObject rootObj;
     rootObj.insert("name", name);
     rootObj.insert("widgets", widgets);
+    rootObj.insert("qssFilePath", qssFilePath);
 
     QJsonObject colorsObj;
     auto insertColor = [&](QPalette::ColorRole role, QString colorName)
@@ -119,75 +160,112 @@ static bool writeThemeJson(const QString &path, const QPalette &palette, double
     }
     catch (const Exception &e)
     {
-        qWarning() << "Failed to write theme json to" << path;
+        themeWarningLog << "Failed to write theme json to" << path;
         return false;
     }
 }
 
-CustomTheme::CustomTheme(ITheme* baseTheme, QString folder)
+/// @brief 
+/// @param baseTheme Base Theme
+/// @param fileInfo FileInfo object for file to load
+/// @param isManifest whether to load a theme manifest or a qss file
+CustomTheme::CustomTheme(ITheme* baseTheme, QFileInfo& fileInfo, bool isManifest)
 {
-    m_id = folder;
+    if (isManifest) {
-    QString path = FS::PathCombine("themes", m_id);
+        m_id = fileInfo.dir().dirName();
-    QString pathResources = FS::PathCombine("themes", m_id, "resources");
 
-    qDebug() << "Loading theme" << m_id;
+        QString path = FS::PathCombine("themes", m_id);
+        QString pathResources = FS::PathCombine("themes", m_id, "resources");
 
-    if(!FS::ensureFolderPathExists(path) || !FS::ensureFolderPathExists(pathResources))
+        if(!FS::ensureFolderPathExists(path) || !FS::ensureFolderPathExists(pathResources))
-    {
-        qWarning() << "couldn't create folder for theme!";
-        m_palette = baseTheme->colorScheme();
-        m_styleSheet = baseTheme->appStyleSheet();
-        return;
-    }
-
-    auto themeFilePath = FS::PathCombine(path, themeFile);
-
-    m_palette = baseTheme->colorScheme();
-    if (!readThemeJson(themeFilePath, m_palette, m_fadeAmount, m_fadeColor, m_name, m_widgets))
-    {
-        m_name = "Custom";
-        m_palette = baseTheme->colorScheme();
-        m_fadeColor = baseTheme->fadeColor();
-        m_fadeAmount = baseTheme->fadeAmount();
-        m_widgets = baseTheme->qtTheme();
-
-        QFileInfo info(themeFilePath);
-        if(!info.exists())
         {
-            writeThemeJson(themeFilePath, m_palette, m_fadeAmount, m_fadeColor, "Custom", m_widgets);
+            themeWarningLog << "X couldn't create folder for theme!";
-        }
+            m_palette = baseTheme->colorScheme();
-    }
-    else
-    {
-        m_palette = fadeInactive(m_palette, m_fadeAmount, m_fadeColor);
-    }
-
-    auto cssFilePath = FS::PathCombine(path, styleFile);
-    QFileInfo info (cssFilePath);
-    if(info.isFile())
-    {
-        try
-        {
-            // TODO: validate css?
-            m_styleSheet = QString::fromUtf8(FS::read(cssFilePath));
-        }
-        catch (const Exception &e)
-        {
-            qWarning() << "Couldn't load css:" << e.cause() << "from" << cssFilePath;
             m_styleSheet = baseTheme->appStyleSheet();
+            return;
         }
-    }
+
-    else
+        auto themeFilePath = FS::PathCombine(path, themeFile);
-    {
+
-        qDebug() << "No theme css present.";
+        bool jsonDataIncomplete = false;
-        m_styleSheet = baseTheme->appStyleSheet();
+
+        m_palette = baseTheme->colorScheme();
+        if (!readThemeJson(themeFilePath, m_palette, m_fadeAmount, m_fadeColor, m_name, m_widgets, m_qssFilePath, jsonDataIncomplete))
+        {
+            themeDebugLog << "Did not read theme json file correctly, writing new one to: " << themeFilePath;
+            m_name = "Custom";
+            m_palette = baseTheme->colorScheme();
+            m_fadeColor = baseTheme->fadeColor();
+            m_fadeAmount = baseTheme->fadeAmount();
+            m_widgets = baseTheme->qtTheme();
+            m_qssFilePath = "themeStyle.css";
+
+            QFileInfo info(themeFilePath);
+        }
+        else
+        {
+            m_palette = fadeInactive(m_palette, m_fadeAmount, m_fadeColor);
+        }
+
+        if(jsonDataIncomplete)
+        {
+            writeThemeJson(fileInfo.absoluteFilePath(), m_palette, m_fadeAmount, m_fadeColor, m_name, m_widgets, m_qssFilePath);
+        }
+
+        auto cssFilePath = FS::PathCombine(path, m_qssFilePath);
+        QFileInfo info (cssFilePath);
+        if(info.isFile())
+        {
+            try
+            {
+                // TODO: validate css?
+                m_styleSheet = QString::fromUtf8(FS::read(cssFilePath));
+            }
+            catch (const Exception &e)
+            {
+                themeWarningLog << "X Couldn't load css:" << e.cause() << "from" << cssFilePath;
+                m_styleSheet = baseTheme->appStyleSheet();
+            }
+        }
+        else
+        {
+            themeDebugLog << "X No theme css present.";
+            m_styleSheet = baseTheme->appStyleSheet();
+            try
+            {
+                FS::write(cssFilePath, m_styleSheet.toUtf8());
+            }
+            catch (const Exception &e)
+            {
+                themeWarningLog << "X Couldn't write css:" << e.cause() << "to" << cssFilePath;
+            }
+        }
+    } else {
+        m_id = fileInfo.fileName();
+        m_name = fileInfo.baseName();
+        QString path = fileInfo.filePath();
+        //themeDebugLog << "Theme ID: " << m_id;
+        //themeDebugLog << "Theme Name: " << m_name;
+        //themeDebugLog << "Theme Path: " << path;
+
+        if(!FS::ensureFilePathExists(path))
+        {
+            themeWarningLog << m_name << " Theme file path doesn't exist!";
+            m_palette = baseTheme->colorScheme();
+            m_styleSheet = baseTheme->appStyleSheet();
+            return;
+        }
+
+        m_palette = baseTheme->colorScheme();
         try
         {
-            FS::write(cssFilePath, m_styleSheet.toUtf8());
+            // TODO: validate qss?
+            m_styleSheet = QString::fromUtf8(FS::read(path));
         }
         catch (const Exception &e)
         {
-            qWarning() << "Couldn't write css:" << e.cause() << "to" << cssFilePath;
+            themeWarningLog << "Couldn't load qss:" << e.cause() << "from" << path;
+            m_styleSheet = baseTheme->appStyleSheet();
         }
     }
 }

launcher/ui/themes/CustomTheme.h

@@ -1,11 +1,51 @@
+// SPDX-License-Identifier: GPL-3.0-only
+/*
+ *  Prism Launcher
+ *  Copyright (C) 2022 Tayou <tayou@gmx.net>
+ *
+ *  This program is free software: you can redistribute it and/or modify
+ *  it under the terms of the GNU General Public License as published by
+ *  the Free Software Foundation, version 3.
+ *
+ *  This program is distributed in the hope that it will be useful,
+ *  but WITHOUT ANY WARRANTY; without even the implied warranty of
+ *  MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ *  GNU General Public License for more details.
+ *
+ *  You should have received a copy of the GNU General Public License
+ *  along with this program.  If not, see <https://www.gnu.org/licenses/>.
+ *
+ * This file incorporates work covered by the following copyright and
+ * permission notice:
+ *
+ *      Copyright 2013-2021 MultiMC Contributors
+ *
+ *      Authors: Andrew Okin
+ *               Peterix
+ *               Orochimarufan <orochimarufan.x3@gmail.com>
+ *
+ *      Licensed under the Apache License, Version 2.0 (the "License");
+ *      you may not use this file except in compliance with the License.
+ *      You may obtain a copy of the License at
+ *
+ *          http://www.apache.org/licenses/LICENSE-2.0
+ *
+ *      Unless required by applicable law or agreed to in writing, software
+ *      distributed under the License is distributed on an "AS IS" BASIS,
+ *      WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ *      See the License for the specific language governing permissions and
+ *      limitations under the License.
+ */
 #pragma once
 
 #include "ITheme.h"
+#include <QFile>
+#include <QDir>
 
 class CustomTheme: public ITheme
 {
 public:
-    CustomTheme(ITheme * baseTheme, QString folder);
+    CustomTheme(ITheme * baseTheme, QFileInfo& file, bool isManifest);
     virtual ~CustomTheme() {}
 
     QString id() override;
@@ -27,5 +67,6 @@ private: /* data */
     QString m_name;
     QString m_id;
     QString m_widgets;
+    QString m_qssFilePath;
 };
 

launcher/ui/themes/SystemTheme.cpp

@@ -1,30 +1,69 @@
+// SPDX-License-Identifier: GPL-3.0-only
+/*
+ *  Prism Launcher
+ *  Copyright (C) 2022 Tayou <tayou@gmx.net>
+ *
+ *  This program is free software: you can redistribute it and/or modify
+ *  it under the terms of the GNU General Public License as published by
+ *  the Free Software Foundation, version 3.
+ *
+ *  This program is distributed in the hope that it will be useful,
+ *  but WITHOUT ANY WARRANTY; without even the implied warranty of
+ *  MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ *  GNU General Public License for more details.
+ *
+ *  You should have received a copy of the GNU General Public License
+ *  along with this program.  If not, see <https://www.gnu.org/licenses/>.
+ *
+ * This file incorporates work covered by the following copyright and
+ * permission notice:
+ *
+ *      Copyright 2013-2021 MultiMC Contributors
+ *
+ *      Authors: Andrew Okin
+ *               Peterix
+ *               Orochimarufan <orochimarufan.x3@gmail.com>
+ *
+ *      Licensed under the Apache License, Version 2.0 (the "License");
+ *      you may not use this file except in compliance with the License.
+ *      You may obtain a copy of the License at
+ *
+ *          http://www.apache.org/licenses/LICENSE-2.0
+ *
+ *      Unless required by applicable law or agreed to in writing, software
+ *      distributed under the License is distributed on an "AS IS" BASIS,
+ *      WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ *      See the License for the specific language governing permissions and
+ *      limitations under the License.
+ */
 #include "SystemTheme.h"
 #include <QApplication>
 #include <QStyle>
 #include <QStyleFactory>
 #include <QDebug>
+#include "ThemeManager.h"
 
 SystemTheme::SystemTheme()
 {
-    qDebug() << "Determining System Theme...";
+    themeDebugLog << "Determining System Theme...";
     const auto & style = QApplication::style();
     systemPalette = style->standardPalette();
     QString lowerThemeName = style->objectName();
-    qDebug() << "System theme seems to be:" << lowerThemeName;
+    themeDebugLog << "System theme seems to be:" << lowerThemeName;
     QStringList styles = QStyleFactory::keys();
     for(auto &st: styles)
     {
-        qDebug() << "Considering theme from theme factory:" << st.toLower();
+        themeDebugLog << "Considering theme from theme factory:" << st.toLower();
         if(st.toLower() == lowerThemeName)
         {
             systemTheme = st;
-            qDebug() << "System theme has been determined to be:" << systemTheme;
+            themeDebugLog << "System theme has been determined to be:" << systemTheme;
             return;
         }
     }
     // fall back to fusion if we can't find the current theme.
     systemTheme = "Fusion";
-    qDebug() << "System theme not found, defaulted to Fusion";
+    themeDebugLog << "System theme not found, defaulted to Fusion";
 }
 
 void SystemTheme::apply(bool initial)

launcher/ui/themes/ThemeManager.cpp

@@ -0,0 +1,152 @@
+// SPDX-License-Identifier: GPL-3.0-only
+/*
+ *  Prism Launcher
+ *  Copyright (C) 2022 Tayou <tayou@gmx.net>
+ *
+ *  This program is free software: you can redistribute it and/or modify
+ *  it under the terms of the GNU General Public License as published by
+ *  the Free Software Foundation, version 3.
+ *
+ *  This program is distributed in the hope that it will be useful,
+ *  but WITHOUT ANY WARRANTY; without even the implied warranty of
+ *  MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ *  GNU General Public License for more details.
+ *
+ *  You should have received a copy of the GNU General Public License
+ *  along with this program.  If not, see <https://www.gnu.org/licenses/>.
+ */
+#include "ThemeManager.h"
+
+#include "ui/themes/SystemTheme.h"
+#include "ui/themes/DarkTheme.h"
+#include "ui/themes/BrightTheme.h"
+#include "ui/themes/CustomTheme.h"
+#include <QDir>
+#include <QDirIterator>
+#include <QIcon>
+#include <QApplication>
+
+#include "Application.h"
+
+#ifdef Q_OS_WIN
+#include <versionhelpers.h>
+#include "ui/WinDarkmode.h"
+#endif
+
+ThemeManager::ThemeManager(MainWindow* mainWindow) {
+    m_mainWindow = mainWindow;
+}
+
+/// @brief Adds the Theme to the list of themes
+/// @param theme The Theme to add
+/// @return Theme ID
+QString ThemeManager::AddTheme(ITheme * theme) {
+    m_themes.insert(std::make_pair(theme->id(), std::unique_ptr<ITheme>(theme)));
+    return theme->id();
+}
+
+/// @brief Gets the Theme from the List via ID
+/// @param themeId Theme ID of theme to fetch
+/// @return Theme at themeId
+ITheme* ThemeManager::GetTheme(QString themeId) {
+    return m_themes[themeId].get();
+}
+
+void ThemeManager::InitializeThemes() {
+    
+
+    // Icon themes
+    {
+        // TODO: icon themes and instance icons do not mesh well together. Rearrange and fix discrepancies!
+        // set icon theme search path!
+        auto searchPaths = QIcon::themeSearchPaths();
+        searchPaths.append("iconthemes");
+        QIcon::setThemeSearchPaths(searchPaths);
+        themeDebugLog << "<> Icon themes initialized.";
+    }
+
+    // Initialize widget themes
+    {
+        themeDebugLog << "<> Initializing Widget Themes";
+        themeDebugLog "✓ Loading Built-in Theme:" << AddTheme(new SystemTheme());
+        auto darkThemeId = AddTheme(new DarkTheme());
+        themeDebugLog "✓ Loading Built-in Theme:" << darkThemeId;
+        themeDebugLog "✓ Loading Built-in Theme:" << AddTheme(new BrightTheme());
+
+        // TODO: need some way to differentiate same name themes in different subdirectories (maybe smaller grey text next to theme name in dropdown? Dunno how to do that though)
+        QString themeFolder = (new QDir("./themes/"))->absoluteFilePath("");
+        themeDebugLog << "Theme Folder Path: " << themeFolder;
+
+        QDirIterator directoryIterator(themeFolder, QDir::Dirs | QDir::NoDotAndDotDot, QDirIterator::Subdirectories);
+        while (directoryIterator.hasNext()) {
+            QDir dir(directoryIterator.next());
+            QFileInfo themeJson(dir.absoluteFilePath("theme.json"));
+            if (themeJson.exists()) {
+                // Load "theme.json" based themes
+                themeDebugLog "✓ Loading JSON Theme from:" << themeJson.absoluteFilePath();
+                CustomTheme* theme = new CustomTheme(GetTheme(darkThemeId), themeJson, true);
+                AddTheme(theme);
+            } else {
+                // Load pure QSS Themes
+                QDirIterator stylesheetFileIterator(dir.absoluteFilePath(""), {"*.qss", "*.css"}, QDir::Files);
+                while (stylesheetFileIterator.hasNext()) {
+                    QFile customThemeFile(stylesheetFileIterator.next());
+                    QFileInfo customThemeFileInfo(customThemeFile);
+                    themeDebugLog "✓ Loading QSS Theme from:" << customThemeFileInfo.absoluteFilePath();
+                    CustomTheme* theme = new CustomTheme(GetTheme(darkThemeId), customThemeFileInfo, false);
+                    AddTheme(theme);
+                }
+            }
+        }
+
+        themeDebugLog << "<> Widget themes initialized.";
+    }
+}
+
+std::vector<ITheme *> ThemeManager::getValidApplicationThemes()
+{
+    std::vector<ITheme *> ret;
+    auto iter = m_themes.cbegin();
+    while (iter != m_themes.cend())
+    {
+        ret.push_back((*iter).second.get());
+        iter++;
+    }
+    return ret;
+}
+
+void ThemeManager::setIconTheme(const QString& name)
+{
+    QIcon::setThemeName(name);
+}
+
+void ThemeManager::applyCurrentlySelectedTheme() {
+    setIconTheme(APPLICATION->settings()->get("IconTheme").toString());
+    themeDebugLog() << "<> Icon theme set.";
+    setApplicationTheme(APPLICATION->settings()->get("ApplicationTheme").toString(), true);
+    themeDebugLog() << "<> Application theme set.";
+}
+
+void ThemeManager::setApplicationTheme(const QString& name, bool initial)
+{
+    auto systemPalette = qApp->palette();
+    auto themeIter = m_themes.find(name);
+    if(themeIter != m_themes.end())
+    {
+        auto & theme = (*themeIter).second;
+        theme->apply(initial);
+#ifdef Q_OS_WIN
+        if (m_mainWindow && IsWindows10OrGreater()) {
+            if (QString::compare(theme->id(), "dark") == 0) {
+                    WinDarkmode::setDarkWinTitlebar(m_mainWindow->winId(), true);
+            } else {
+                    WinDarkmode::setDarkWinTitlebar(m_mainWindow->winId(), false);
+            }
+        }
+#endif
+    }
+    else
+    {
+        qWarning() << "Tried to set invalid theme:" << name;
+    }
+}

launcher/ui/themes/ThemeManager.h

@@ -0,0 +1,44 @@
+// SPDX-License-Identifier: GPL-3.0-only
+/*
+ *  Prism Launcher
+ *  Copyright (C) 2022 Tayou <tayou@gmx.net>
+ *
+ *  This program is free software: you can redistribute it and/or modify
+ *  it under the terms of the GNU General Public License as published by
+ *  the Free Software Foundation, version 3.
+ *
+ *  This program is distributed in the hope that it will be useful,
+ *  but WITHOUT ANY WARRANTY; without even the implied warranty of
+ *  MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ *  GNU General Public License for more details.
+ *
+ *  You should have received a copy of the GNU General Public License
+ *  along with this program.  If not, see <https://www.gnu.org/licenses/>.
+ */
+
+#include <QString>
+
+#include "ui/themes/ITheme.h"
+#include "ui/MainWindow.h"
+
+#define themeDebugLog qDebug() << "[Themes]"
+#define themeWarningLog qWarning() << "[Themes]"
+
+class ThemeManager {
+public:
+    ThemeManager(MainWindow* mainWindow);
+    void InitializeThemes();
+
+    std::vector<ITheme *> getValidApplicationThemes();
+    void setIconTheme(const QString& name);
+    void applyCurrentlySelectedTheme();
+    void setApplicationTheme(const QString& name, bool initial);
+
+private:
+    std::map<QString, std::unique_ptr<ITheme>> m_themes;
+    MainWindow* m_mainWindow;
+
+    QString AddTheme(ITheme * theme);
+    ITheme* GetTheme(QString themeId);
+};
+