Add UI Feature

UI (scene root)
├── Main Canvas (UIDocument + UIController)
│   └── UI Toolkit visual tree (UXML)
├── InfoDisplay (legacy TextMeshPro overlay)
└── FollowingTargetList

<ui:Button name="MyFeature" text="My Feature" class="toolbar-button" />

// Add field
private Button _buttonMyFeature = null;

// In Start(), after other button wiring:
_buttonMyFeature = _rootVisualElement.Q<Button>("MyFeature");
_buttonMyFeature.clickable.clicked += () => OnMyFeatureClicked();

// Optionally add hover effects:
_buttonMyFeature.RegisterCallback<MouseEnterEvent>(
    delegate { ChangeBackground(ref _buttonMyFeature, Color.gray); });
_buttonMyFeature.RegisterCallback<MouseLeaveEvent>(
    delegate { ChangeBackground(ref _buttonMyFeature, Color.clear); });

private void OnMyFeatureClicked()
{
    _buttonMyFeature.ToggleInClassList("selected");
    // Interact with Main singleton:
    Main.Instance.MyNewMethod();
}

// Query by name and type:
_rootVisualElement.Q<Button>("CameraView")
_rootVisualElement.Q<Toggle>("LockVerticalMoving")
_rootVisualElement.Q<TextField>("ScaleField")
_rootVisualElement.Q<Label>("StatusMessage")
_rootVisualElement.Q<EnumField>("MyEnum")
_rootVisualElement.Q<ScrollView>("MyList")
_rootVisualElement.Q<VisualElement>("MyContainer")

// Click
button.clickable.clicked += () => { ... };

// Value change
toggle.RegisterValueChangedCallback(x => DoSomething(x.newValue));

// Focus events
textField.RegisterCallback<FocusOutEvent>(OnFocusOut);

// Mouse events
element.RegisterCallback<MouseEnterEvent>(delegate { ... });
element.RegisterCallback<MouseLeaveEvent>(delegate { ... });

// Visibility
element.style.display = DisplayStyle.None;     // hidden, no layout
element.style.display = DisplayStyle.Flex;      // visible
element.style.visibility = Visibility.Hidden;   // hidden, keeps layout

// Background color
element.style.backgroundColor = new Color(0.5f, 0.5f, 0.5f, 1f);

// CSS class toggling
element.ToggleInClassList("selected");
element.EnableInClassList("active", isActive);
element.AddToClassList("highlight");
element.RemoveFromClassList("highlight");

/*
 * Copyright (c) 2026 LG Electronics Inc.
 *
 * SPDX-License-Identifier: MIT
 */

using UnityEngine;

public class MyCameraControl : CameraControl
{
    protected override void HandleMouseWheelScroll(in float value)
    {
        // Custom zoom behavior
    }

    protected override void HandleKeyboardDirection(in float duration)
    {
        // Custom movement (WASD)
    }
}

// From anywhere with access to Main:
Main.UIController?.SetStatusMessage("Loading model...");
Main.UIController?.SetWarningMessage("Warning text");
Main.UIController?.SetErrorMessage("Error text");
Main.UIController?.ClearMessage();

// Keyboard
if (Keyboard.current[Key.Space].wasPressedThisFrame) { ... }
if (Keyboard.current[Key.LeftCtrl].isPressed) { ... }

// Mouse
var scrollDelta = Mouse.current.scroll.ReadValue().y;
var mousePosition = Mouse.current.position.ReadValue();
if (Mouse.current.leftButton.wasPressedThisFrame) { ... }