Add a page on making a UI controller/keyboard navigable

tutorials/ui/gui_navigation.rst

@@ -0,0 +1,79 @@
+.. _doc_gui_navigation:
+
+Keyboard/Controller Navigation and Focus
+========================================
+
+It is a common requirement for a user interface to have full keyboard
+and controller support for navigation and interaction. There are two main
+reasons why this is beneficial for projects: improved accessibility (not everyone
+can use mouse or touch controls for interactions), and getting your project
+ready for :ref:`consoles <doc_consoles>` (or just for people who prefer
+to game with a controller on PC).
+
+Navigating between UI elements with keyboard or controller is done by
+changing which node is actively selected. This is also called changing UI focus.
+Every :ref:`Control <class_Control>` node in Godot is capable of having focus.
+By default, some control nodes have the ability to automatically grab focus
+reacting to built-in UI actions such as ``ui_up``, ``ui_down``, ``ui_focus_next``, etc.
+These actions can be seen in the project settings in the input map and can be modified.
+
+.. warning::
+
+    Because these actions are used for focus they should not be used for any
+    gameplay code.
+
+Node settings
+-------------
+
+In addition to the built-in logic, you can define what is known as focus neighbors
+for each individual control node. This allows to finely tune the path the UI focus
+takes across the user interface of your project. The settings for individual
+nodes can be found in the Inspector dock, under the "Focus" category of the
+"Control" section.
+
+.. image:: img/focus_settings.png
+
+Neighbor options are used to define nodes for 4-directional navigation, such
+as using arrow keys or a D-pad on a controller. For example, the bottom neighbor
+will be used when navigating down with the down arrow or by pushing down on
+the D-pad. The "Next" and "Previous" options are used with the focus shift button,
+such as :kbd:`Tab` on desktop operating systems.
+
+.. note::
+    A node can lose focus if it becomes hidden.
+
+The mode setting defines how a node can be focused. **All** means a node can
+be focused by clicking on it with the mouse, or selecting it with a keyboard
+or controller. **Click** means it can only be focused on by clicking on it.
+Finally, **None** means it can't be focused at all. Different control nodes have
+different default settings for this based on how they are typically used, for
+example, :ref:`Label <class_Label>` nodes are set to "None" by default,
+while :ref:`buttons <class_Button>` are set to "All".
+
+Make sure to properly configure your scenes for focus and navigation. If a node has
+no focus neighbor configured, the engine will try to guess the next control automatically.
+This may result in unintended behavior, especially in a complex user interface that doesn't
+have well-defined vertical or horizontal navigation flow.
+
+Necessary code
+--------------
+
+For keyboard and controller navigation to work correctly, any node must be focused on
+using code when the scene starts. Without doing this, pressing buttons or keys won't
+do anything. Here is a basic example of setting initial focus with code:
+
+.. tabs::
+ .. code-tab:: gdscript GDScript
+
+    func _ready():
+        $StartButton.grab_focus()
+
+ .. code-tab:: csharp
+
+    public override void _Ready()
+    {
+        GetNode<Button>("StartButton").GrabFocus();
+    }
+
+Now when the scene starts the "Start Button" node will be focused, and the keyboard
+or a controller can be used to navigate between it and other UI elements.