[qt] refactor: qt_common lib (#94)

This is part of a series of PRs made in preparation for the QML rewrite. this PR specifically moves a bunch of utility functions from main.cpp into qt_common, with the biggest benefit being that QML can reuse the exact same code through ctx passthrough.

Also, QtCommon::Frontend is an abstraction layer over several previously Widgets-specific stuff like QMessageBox that gets used everywhere. The idea is that once QML is implemented, these functions can have a Quick version implemented for systems that don't work well with Widgets (sun) or for those on Plasma 6+ (reduces memory usage w/o Widgets linkage) although Quick from C++ is actually anal, but whatever.

Other than that this should also just kinda reduce the size of main.cpp which is a 6000-line behemoth rn, and clangd straight up gives up with it for me (likely caused by the massive amount of headers, which this DOES reduce).

In the future, I probably want to create a common strings lookup table that both Qt and QML can reference--though I'm not sure how much linguist likes that--which should give us a way to keep language consistent (use frozen-map).

TODO: Docs for Qt stuff

Co-authored-by: MaranBr <maranbr@outlook.com>
Reviewed-on: eden-emu/eden#94
Reviewed-by: MaranBr <maranbr@eden-emu.dev>
Reviewed-by: Shinmegumi <shinmegumi@eden-emu.dev>

src/qt_common/uisettings.cpp

@@ -0,0 +1,110 @@
+// SPDX-FileCopyrightText: Copyright 2025 Eden Emulator Project
+// SPDX-License-Identifier: GPL-3.0-or-later
+
+// SPDX-FileCopyrightText: 2016 Citra Emulator Project
+// SPDX-License-Identifier: GPL-2.0-or-later
+
+#include <QSettings>
+#include "common/fs/fs.h"
+#include "common/fs/path_util.h"
+#include "qt_common/uisettings.h"
+
+#ifndef CANNOT_EXPLICITLY_INSTANTIATE
+namespace Settings {
+template class Setting<bool>;
+template class Setting<std::string>;
+template class Setting<u16, true>;
+template class Setting<u32>;
+template class Setting<u8, true>;
+template class Setting<u8>;
+template class Setting<unsigned long long>;
+} // namespace Settings
+#endif
+
+namespace FS = Common::FS;
+
+namespace UISettings {
+
+const Themes themes{{
+    {"Default", "default"},
+    {"Default Colorful", "colorful"},
+    {"Dark", "qdarkstyle"},
+    {"Dark Colorful", "colorful_dark"},
+    {"Midnight Blue", "qdarkstyle_midnight_blue"},
+    {"Midnight Blue Colorful", "colorful_midnight_blue"},
+}};
+
+bool IsDarkTheme() {
+    const auto& theme = UISettings::values.theme;
+    return theme == std::string("qdarkstyle") || theme == std::string("qdarkstyle_midnight_blue") ||
+           theme == std::string("colorful_dark") || theme == std::string("colorful_midnight_blue");
+}
+
+Values values = {};
+
+u32 CalculateWidth(u32 height, Settings::AspectRatio ratio) {
+    switch (ratio) {
+    case Settings::AspectRatio::R4_3:
+        return height * 4 / 3;
+    case Settings::AspectRatio::R21_9:
+        return height * 21 / 9;
+    case Settings::AspectRatio::R16_10:
+        return height * 16 / 10;
+    case Settings::AspectRatio::R16_9:
+    case Settings::AspectRatio::Stretch:
+        // TODO: Move this function wherever appropriate to implement Stretched aspect
+        break;
+    }
+    return height * 16 / 9;
+}
+
+void SaveWindowState() {
+    const auto window_state_config_loc =
+        FS::PathToUTF8String(FS::GetEdenPath(FS::EdenPath::ConfigDir) / "window_state.ini");
+
+    void(FS::CreateParentDir(window_state_config_loc));
+    QSettings config(QString::fromStdString(window_state_config_loc), QSettings::IniFormat);
+
+    config.setValue(QStringLiteral("geometry"), values.geometry);
+    config.setValue(QStringLiteral("state"), values.state);
+    config.setValue(QStringLiteral("geometryRenderWindow"), values.renderwindow_geometry);
+    config.setValue(QStringLiteral("gameListHeaderState"), values.gamelist_header_state);
+
+    config.sync();
+}
+
+void RestoreWindowState(std::unique_ptr<QtConfig>& qtConfig) {
+    const auto window_state_config_loc =
+        FS::PathToUTF8String(FS::GetEdenPath(FS::EdenPath::ConfigDir) / "window_state.ini");
+
+    // Migrate window state from old location
+    if (!FS::Exists(window_state_config_loc) && qtConfig->Exists("UI", "UILayout\\geometry")) {
+        const auto config_loc =
+            FS::PathToUTF8String(FS::GetEdenPath(FS::EdenPath::ConfigDir) / "qt-config.ini");
+        QSettings config(QString::fromStdString(config_loc), QSettings::IniFormat);
+
+        config.beginGroup(QStringLiteral("UI"));
+        config.beginGroup(QStringLiteral("UILayout"));
+        values.geometry = config.value(QStringLiteral("geometry")).toByteArray();
+        values.state = config.value(QStringLiteral("state")).toByteArray();
+        values.renderwindow_geometry =
+            config.value(QStringLiteral("geometryRenderWindow")).toByteArray();
+        values.gamelist_header_state =
+            config.value(QStringLiteral("gameListHeaderState")).toByteArray();
+        config.endGroup();
+        config.endGroup();
+        return;
+    }
+
+    void(FS::CreateParentDir(window_state_config_loc));
+    const QSettings config(QString::fromStdString(window_state_config_loc), QSettings::IniFormat);
+
+    values.geometry = config.value(QStringLiteral("geometry")).toByteArray();
+    values.state = config.value(QStringLiteral("state")).toByteArray();
+    values.renderwindow_geometry =
+        config.value(QStringLiteral("geometryRenderWindow")).toByteArray();
+    values.gamelist_header_state =
+        config.value(QStringLiteral("gameListHeaderState")).toByteArray();
+}
+
+} // namespace UISettings