Add RFC: Switch to Advanced Docking System

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+# Summary
+
+- Switch main dock system to [ADS][1]
+- Make ADS dock state per profile
+- Allow the user to switch between pre-made layouts
+  - Plugins could register their own
+  - Users could save their own
+- Dock added by plugins with the old methods are added as "*Legacy dock*"
+
+Note: The "central widget" design is kept.
+
+# Motivation
+
+Provide a better dock system to end-users.
+
+# Design
+**DISCLAIMER**: The "central widget" design is kept, switching to a non-"central widget" one is not part of this RFC.
+
+## Main window dock separation
+To make OBS Studio compatible with ADS, Controls, Transitions, Mixer, Sources, Scenes docks need to be separated from the main window.
+
+And the central widget of main window should also be separated as well to become the central dock.
+
+So the docks will be separated as widget class with their own UI class.
+
+Then those widget are inserted in OBSDock (QDockWidget) and the central widget and put as main window central widget.
+
+And then we switch to ADS, all those widget will become docks and added to the ADS dock manager.
+
+The OBSBasic heavily rely on some UI element from those docks, to resolve that the related code will be refactored to remove this dependance going toward a MVC pattern.
+
+Each widget class will be put as a friend class in OBSBasic to allow access to private slot and avoid moving them as public.
+
+### Controls widget
+*Future ADS Controls dock widget*
+
+All the buttons of this dock will be connected through signal and slots to OBSBasic.
+
+Some hotkeys and pause functions rely on UI buttons, so OBS Basic will be refactored to remove this dependance.
+
+### Transistions widget
+*Future ADS Transitions dock widget*
+
+Transitions will be stored in OBSBasic and selected through the combo box of the widget.
+
+The transition duration will become an attribute of OBSBasic, and signal and slots will be setup to synchromise it with the dock spinbox.
+
+Buttons for adding, removing and open settings will be connected through signals and slots to OBSBasic.
+
+### Mixer widget
+*Future ADS Mixer dock widget*
+
+The base dock is easily separable, but the VolControl class can be refactored (toward MVC) later because this is not a requirement for this RFC.
+
+### Sources widget
+*Future ADS Sources dock widget*
+
+OBSBasic heavily rely on the SourceTree from the widget, but a refactoring will not be considered as a requirement for this RFC. So the class of the sources widget will have OBSBasic as a friend class.
+
+### Scenes widget
+*Future ADS Scenes dock widget*
+
+OBSBasic heavily rely on the SceneTree from the widget, but a refactoring will not be considered as a requirement for this RFC. So the class of the scenes widget will have OBSBasic as a friend class.
+
+### Central widget
+*Future ADS Central dock widget*
+
+Some context bar, preview/program and nudge related code is moved to the central widget class.
+
+This class will have OBSBasicPreview as a friend class.
+
+This class will be a friend class of OBSBasic also to have access to some gs_vertbuffer_t type attributes.
+
+## ADS
+The Advanced Docking System, require to add a Dock Manager in the main window and then add the central widget and then add other docks.
+
+Some work on themes CSS will be required.
+
+### About obs-deps
+
+obs-deps already build Qt for macOS and Windows, so adding a ADS script to the Qt tarballs is not a problem.
+
+### Floating docks titlebar on X11
+On X11, ADS provide two type of titlebar for floating docks:
+
+- Native
+
+[![Native titlebar under GNOME](./0047-switch-to-advanced-docking-system/linux_native_floating_dock_titlebar.png)]()
+
+- QWidget based (WIP CSS)
+
+[![QWidget titlebar](./0047-switch-to-advanced-docking-system/linux_qwidget_floating_dock_titlebar.png)]()
+
+The QWidget one is used by default when using KWin based Desktop Environement like Plasma. And this titlebar requires some CSS in the themes to match it.
+
+So the QWidget based titlebar usage will be enforced thanks to a flag for the Dock Manager to "unify" experience between desktop environement.
+Theme makers may ignore to theme this bar.
+
+### Dock state
+*The per profile dock state feature is not taken into account to describe those changes.*
+
+In the global config (`global.ini`).
+- `"dockState"` is kept for for backward compatiblity and no longer overwitten. It will be used if the following state is not present.
+- `"windowState"` is the state of the main window, since it does not store only the state of legacy docks.
+- `"advDockState"` is the state of the dock manager which contain only the states of any ADS dock.
+
+Service integrations only save `"advDockProfile"`
+
+ADS dock state is compressed by default but behind the scene it's XML.
+
+### OBSAdvDock
+OBSAdvDock is a class which inherit `ads::CDockWidget` class.
+
+This class has a constructor which require a QWidget and setup some things arround the widget and set some connections.
+
+It adds a warning message when closing a dock from a close dock button.
+
+It allows to reset a dock position after a UI reset or a layout change with a possibility to reset the size if set beforehand.
+
+### Custom Browser docks and BrowserAdvDock
+The custom browser docks feature is modified to use BrowserAdvDock which inherit OBSAdvDock.
+
+Those docks are stored in the dock manager and their names is stored in a QStringList for browser docks to be able to get the dock from the manager to modify it like changing the URL.
+
+Each of those browser dock is named `extraBrowser_$UUID` where `$UUID` is replaced by the dock UUID to have a really unique name.
+
+### Service integration docks
+
+Like custom browser docks, those integration are modified to use BrowserAdvDock. But their names is stored in the QStringList for plugins extra docks.
+
+Those docks are named `obs-$SERVICE_$DOCK_NAME` where `$SERVICE` is the service name in lowercase and `$DOCK_NAME` the name of the dock.
+
+`"dockState"` will be imported from the integration config if `"windowState"` is not present.
+
+### Reset UI action
+1. Legacy dock are hidden
+2. The default state written in XML is applied
+3. Each not shown OBSAdvDock/BrowserAdvDock dock have its position and size reseted.
+
+## Legacy dock
+
+**TODO: Talk about `obs_frontend_add_custom_qdock()`**
+
+The frontend API method `obs_frontend_add_dock()` is put in deprecation. And if dual switch only Qt5 and on Qt 6 the method is removed or does nothing, this is possible because plugin will need to be rebuilt agaisnt Qt6.
+
+And dock added through this method are added to a sub-menu named `Legacy dock` of the Dock menu.
+
+[![Legacy dock menu](./0047-switch-to-advanced-docking-system/legacy_dock.png)]()
+
+When openning a legacy dock, a message will appear explaining that those docks will not meld wery well with "new" docks.
+
+The state of those are saved through `"windowState"` global config.
+
+## Per profile dock state
+Move the `"advDockState"` from global config to the profile and integration no longer store their own state. `"windowState"` is kept global.
+
+If a release happen between the switch to ADS and this feature, import the one from the integration service if the profile has one set up.
+
+## Layouts management
+Add the feature, to switch between registered/saved dock layouts:
+- Though a sub-menu in the dock menu
+- Through a hotkey
+- Through the frontend API
+
+OBS Studio could provide layouts, the default count as one.
+
+Plugins could also register their own XML layouts through the frontend API.
+
+Users could be able to save their own layouts. Those layouts will have their name prefixed with`user_` to avoid name conflicts.
+
+Note: ADS perspective feature is not directly used because it relies heavily on QSettings.
+## Frontend API
+
+**TODO: Talk about obs_frontend_add_dock_by_id() that is now a thing**
+
+This allow to add a OBSAdvDock with the given QWidget. Those docks are stored in the Dock Manager and their names is stored in the QStringList for plugins extra docks.
+
+Default height and width would based on the widget actual size.
+
+Minimum sizes used by the dock are based on the widget ones.
+
+### Remove a dock
+
+**TODO: Talk about `obs_frontend_remove_dock()` that is now a thing**
+
+### Add a dock layouts
+
+**TODO: Refactor API design**
+
+```c++
+#define obs_frontend_add_dock_layout(title, unique_name, xml_layout) \
+	obs_frontend_add_module_dock_layout(obs_current_module(),    \
+					 title, unique_name, xml_layout)
+EXPORT void obs_frontend_add_module_dock_layout(obs_module_t *module,
+					     const char *title,
+					     const char *unique_name,
+					     const char *xml_layout);
+```
+
+This allow the plugin to add a dock layouts in XML to the UI. ADS allow to test a layout (state/perspective) without applying it, so the layout will be tested before registering it.
+
+### Get a list of docks layouts
+```c++
+EXPORT char **obs_frontend_get_dock_layouts(void);
+```
+
+This allow the plugin to get a list of registered dock layouts from the UI.
+
+### Set a registered dock layout
+```c++
+EXPORT void obs_frontend_set_dock_layouts(const char *layout_name);
+```
+
+This allow the plugin to set a registered dock layouts to the UI, the asked name should come directly from the get list method.
+
+### Remove a dock layouts
+
+**TODO: Refactor API design**
+
+```c++
+#define obs_frontend_remove_dock_layout(unique_name) \
+	obs_frontend_remove_module_dock_layout(obs_current_module(), \
+			unique_name)
+EXPORT void obs_frontend_remove_module_dock_layout(obs_module_t *module,
+						const char *unique_name);
+```
+
+This allow the plugin to remove a dock layouts from the UI.
+
+### Add a entirely custom dock
+
+**TODO: Redo as those will be only legacy docks**
+
+```c++
+/* takes ads::CDockWidget */
+#define obs_frontend_add_custom_dock(unique_name, dock)           \
+	obs_frontend_add_module_custom_dock(obs_current_module(), \
+						unique_name, dock)
+EXPORT void obs_frontend_add_module_custom_dock(obs_module_t *module,
+						    const char *unique_name,
+						    void *dock);
+```
+
+Some plugin like [Sources Dock][6], do not add their docks to the Dock menu.
+
+So this method allow to do this but requires the plugin to be link against ADS library.
+
+And the dock will not have OBSAdvDock features.
+
+Even if the plugin has the control over the dock, the the name is changed by the frontend API to be prefixed by the module name.
+
+`obs_frontend_remove_dock()` can be used to remove the reference stored in the Dock Manager. Because their names is stored in the QStringList for plugins custom extra docks.
+
+### Get the XML behind a registered dock layout
+*Method meant to allow a Dock Layout editor tool to exist*
+
+```c++
+EXPORT char *obs_frontend_get_dock_layout(const char *layout_name);
+```
+
+This allow the plugin to get a registered dock layouts XML, the asked name should come directly from the get list method.
+
+### Get the XML of the actual dock state
+*Method meant to allow a Dock Layout editor tool to exist*
+
+```c++
+EXPORT char *obs_frontend_get_current_dock_state(void);
+```
+
+This allow the plugin to get the dock states XML of the UI.
+
+### Events addition
+- An event before the startup restore dock state and `OBS_FRONTEND_EVENT_FINISHED_LOADING` to allow plugins to load their docks before the restore or redo a restore if the number of extra docks has changed. This event could possibly be emitted when profile is changed before restoring profile dock state and `OBS_FRONTEND_EVENT_PROFILE_CHANGED`.
+
+- An event when the a dock layout is applied (reset or not) to allow plugins to reset the positions of their customs docks, if they want to.
+
+## About making dock states future proof
+By default generated state are version 0. If one day we make a breaking change like remove the notion of central widget and so change the version.
+
+We could take the saved `"advDockState"` and uncompress to edit the XML, to make it compatible with the change.
+
+# Drawbacks
+We can't convert old `"dockState"` to the new dock system.
+
+# Additional Information
+About Wayland support, Qt and ADS docking system have very bad support because of Qt Wayland. The Wayland backend is apparently third-class on Qt's priorities.
+
+My WIP branches:
+- [Dock separation][2]
+- [Central widget separation][8]
+- [Switch to ADS][3]
+- [Frontend API to add ADS dock][4]
+- [Frontend API to add custom ADS dock][5]
+
+[1]: https://github.com/githubuser0xFFFF/Qt-Advanced-Docking-System
+[2]: https://github.com/tytan652/obs-studio/tree/dock_separation
+[3]: https://github.com/tytan652/obs-studio/tree/advanced_docking
+[4]: https://github.com/tytan652/obs-studio/tree/ads_frontend_api
+[5]: https://github.com/tytan652/obs-studio/tree/add_custom_dock
+[6]: https://obsproject.com/forum/resources/source-dock.1317/
+[7]: https://doc.qt.io/qt-5/qobject.html#setProperty
+[8]: https://github.com/tytan652/obs-studio/tree/central_widget_separation