Version: 2021.3
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Performance consideration for runtime UI
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FAQ for input and event systems with UI Toolkit

This page includes frequently asked questions for using the event systemA way of sending events to objects in the application based on input, be it keyboard, mouse, touch, or custom input. The Event System consists of a few components that work together to send events. More info
See in Glossary
and the input system with UI(User Interface) Allows a user to interact with your application. Unity currently supports three UI systems. More info
See in Glossary
Toolkit.

  1. How do I know if the mouse is over a visual element from a runtime panel?
  2. How can I remap basic UI actions?
  3. How can I change what element is focused next when using directional navigation?
  4. Is it possible to get rid of WASD inputs for directional navigation or space bar for the submit action?
  5. How can I start entering keyboard input without ever clicking anywhere with the mouse?

How do I know if the mouse is over a visual element from a runtime panel?

You can do this by two methods:

First method

  1. Add an Event System component in your sceneA Scene contains the environments and menus of your game. Think of each unique Scene file as a unique level. In each Scene, you place your environments, obstacles, and decorations, essentially designing and building your game in pieces. More info
    See in Glossary
    the same way as you create GameObject-based UI content from the com.unity.uGUI package.

  2. Use the EventSystem.current.IsPointerOverGameObject method, which returns true if the pointer is over UI content from either uGUI or from UI Toolkit.

  3. Use the EventSystem.current.RaycastAll method to see what visual elementA node of a visual tree that instantiates or derives from the C# VisualElement class. You can style the look, define the behaviour, and display it on screen as part of the UI. More info
    See in Glossary
    is under the mouse.

  4. Intersected UI Toolkit Panels are represented in the Event System’s environment through a GameObjectThe fundamental object in Unity scenes, which can represent characters, props, scenery, cameras, waypoints, and more. A GameObject’s functionality is defined by the Components attached to it. More info
    See in Glossary
    :

    • The GameObject’s name matches the corresponding PanelSettings.
    • The GameObject’s parent is the GameObject that holds the current Event System component.
    • The GameObject has two components, PanelRaycaster and PanelEventHandler. Both components have a panel property that returns the IPanel it targets.

After you find the panel under the pointer, call the panel.Pick method to find what visual element lies at the pointer’s position.

You must use the RuntimePanelUtils.ScreenToPanel method to transform the pointer’s screen coordinates into panel coordinates.

uGUI’s screen coordinate system uses a bottom-left origin whereas UI Toolkit screen coordinates are expressed from the top-left. Conversion between the two systems requires that you mirror the Y coordinate with yTopLeft = Screen.height - yBottomLeft, and vice versa.

Second method

  1. Use the UIDocument.rootVisualElement property from one UIDocument per distinct PanelSettings used to get the list of all the runtime panels that could be under the pointer, which you can gather
  2. Go through the panels manually in order of depth and call panel.Pick on each of them successively until you find one that returns a visual element.

How can I remap basic UI actions?

To remap basic UI actions:

  1. Add an Event System component in your scene the same way as you create GameObject-based UI content from the com.unity.uGUI package.
  2. In the InspectorA Unity window that displays information about the currently selected GameObject, asset or project settings, allowing you to inspect and edit the values. More info
    See in Glossary
    window, configure the Stand alone Input Module or Input System UI Input Module fields to control what input maps to each action.

Note: The actions mapped to Tab and Shift+Tab inputs can’t be remapped because they’re not exposed through the Event System input modules.

How can I change what element is focused next when using directional navigation?

You can configure directional navigation to have other targets other than the default ones.

The following code example allows element A to navigate to elements U, D, L, R when navigating up, down, left, and right respectively:

A.RegisterCallback <NavigationMoveEvent>(e =>
{
    switch(e.direction)
    {
        case NavigationMoveEvent.Direction.Up: U.Focus(); break;
        case NavigationMoveEvent.Direction.Down: D.Focus(); break;
        case NavigationMoveEvent.Direction.Left: L.Focus(); break;
        case NavigationMoveEvent.Direction.Right: R.Focus(); break;
    }
    e.PreventDefault();
});

Is it possible to get rid of WASD inputs for directional navigation or space bar for the submit action?

Yes. You can use the EventSystem StandaloneInputModule or InputSystemUIInputModule inspector fields to control what input maps to each action. However, since these actions are shared with uGUI input, this also changes the uGUI controls.

To remap UI Toolkit inputs without affecting uGUI controls, disable UI Toolkit’s runtime event handling and send all events manually to panels.

How can I start entering keyboard input without ever clicking anywhere with the mouse?

It’s possible that no element or panel is at focus at a given time, such as when loading your game scene the first time. In this case, keyboard navigation doesn’t start from a predictable first element. This can be a problem for a game that plays entirely without a mouse.

You add C# script to allow a predictable navigation behavior from the start, and attach your script to the same GameObject as the UIDocument responsible for the element that you choose to get the initial focus.

Assume your script is named as FirstFocus and your initial focused element is named as first-focused. In your script’s Start() method, add a line to focus that element as the following:

public class FirstFocus : MonoBehaviour
{
    void Start()
    {
        FocusFirstElement();
    }

    public void FocusFirstElement()
    {
        GetComponent<UIDocument>().rootVisualElement.
            Q<VisualElement>("first-focused").Focus();
    }
}

Note: If you disable the UIDocument’s GameObject, all its underlying hierarchy are recreated from scratch. Therefore, you must run your custom FocusFirstElement() method again after you re-enable the GameObject.

Additional resources

Performance consideration for runtime UI
Work with text
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