Unity uGUI

Overview

Unity's uGUI system provides flexible UI but requires careful optimization to maintain performance, especially on mobile devices.

When to Use

• Game menus and HUD
• Inventory and shop screens
• Scrolling lists
• Modal dialogs
• Health bars and floating text

Canvas Optimization

Canvas Splitting

// WRONG: Everything on one canvas
// Every change causes full rebuild

// RIGHT: Split by update frequency
public class CanvasOrganizer : MonoBehaviour
{
    [Header("Static UI - Never changes")]
    [SerializeField] private Canvas _staticCanvas;  // Background, frames
    
    [Header("Semi-Dynamic - Changes occasionally")]
    [SerializeField] private Canvas _dynamicCanvas; // Buttons, icons
    
    [Header("Highly Dynamic - Changes every frame")]
    [SerializeField] private Canvas _hudCanvas;     // Health, mana, timers
    
    private void Start()
    {
        // Static canvas doesn't need updates
        _staticCanvas.GetComponent<GraphicRaycaster>().enabled = false;
    }
}

Canvas Group for Visibility

public class UIPanel : MonoBehaviour
{
    private CanvasGroup _canvasGroup;
    
    private void Awake()
    {
        _canvasGroup = GetComponent<CanvasGroup>();
    }
    
    // BETTER than SetActive - doesn't rebuild canvas
    public void Show()
    {
        _canvasGroup.alpha = 1f;
        _canvasGroup.interactable = true;
        _canvasGroup.blocksRaycasts = true;
    }
    
    public void Hide()
    {
        _canvasGroup.alpha = 0f;
        _canvasGroup.interactable = false;
        _canvasGroup.blocksRaycasts = false;
    }
    
    public async UniTask FadeIn(float duration)
    {
        _canvasGroup.interactable = true;
        _canvasGroup.blocksRaycasts = true;
        
        float elapsed = 0;
        while (elapsed < duration)
        {
            elapsed += Time.unscaledDeltaTime;
            _canvasGroup.alpha = elapsed / duration;
            await UniTask.Yield();
        }
        _canvasGroup.alpha = 1f;
    }
}

Raycast Optimization

public class RaycastOptimizer : MonoBehaviour
{
    // Disable Raycast Target on non-interactive elements
    public void OptimizeHierarchy()
    {
        var graphics = GetComponentsInChildren<Graphic>(true);
        
        foreach (var graphic in graphics)
        {
            // Only enable on actually clickable items
            bool isInteractive = 
                graphic.GetComponent<Button>() != null ||
                graphic.GetComponent<Toggle>() != null ||
                graphic.GetComponent<Slider>() != null ||
                graphic.GetComponent<ScrollRect>() != null;
            
            graphic.raycastTarget = isInteractive;
        }
    }
}

List Virtualization

Simple Virtual List

public class VirtualizedList<TData, TView> : MonoBehaviour 
    where TView : Component
{
    [SerializeField] private ScrollRect _scrollRect;
    [SerializeField] private RectTransform _content;
    [SerializeField] private TView _itemPrefab;
    [SerializeField] private float _itemHeight = 100f;
    
    private readonly List<TView> _visibleItems = new();
    private readonly Queue<TView> _recycledItems = new();
    private IList<TData> _dataSource;
    private Action<TView, TData> _bindAction;
    
    private int _firstVisibleIndex;
    private float _viewportHeight;
    
    public void Initialize(IList<TData> data, Action<TView, TData> bindAction)
    {
        _dataSource = data;
        _bindAction = bindAction;
        
        // Set content height
        _content.sizeDelta = new Vector2(
            _content.sizeDelta.x,
            data.Count * _itemHeight
        );
        
        _viewportHeight = _scrollRect.viewport.rect.height;
        
        _scrollRect.onValueChanged.AddListener(OnScroll);
        
        RefreshVisibleItems();
    }
    
    private void OnScroll(Vector2 _)
    {
        RefreshVisibleItems();
    }
    
    private void RefreshVisibleItems()
    {
        float scrollY = _content.anchoredPosition.y;
        
        int newFirstVisible = Mathf.Max(0, Mathf.FloorToInt(scrollY / _itemHeight));
        int visibleCount = Mathf.CeilToInt(_viewportHeight / _itemHeight) + 2;
        int lastVisible = Mathf.Min(newFirstVisible + visibleCount, _dataSource.Count);
        
        // Recycle items that scrolled out
        for (int i = _visibleItems.Count - 1; i >= 0; i--)
        {
            var item = _visibleItems[i];
            int itemIndex = GetItemIndex(item);
            
            if (itemIndex < newFirstVisible || itemIndex >= lastVisible)
            {
                RecycleItem(item);
                _visibleItems.RemoveAt(i);
            }
        }
        
        // Create/reuse items that scrolled in
        for (int i = newFirstVisible; i < lastVisible; i++)
        {
            if (!IsItemVisible(i))
            {
                var item = GetOrCreateItem();
                PositionItem(item, i);
                _bindAction(item, _dataSource[i]);
                _visibleItems.Add(item);
            }
        }
        
        _firstVisibleIndex = newFirstVisible;
    }
    
    private TView GetOrCreateItem()
    {
        if (_recycledItems.Count > 0)
        {
            var item = _recycledItems.Dequeue();
            item.gameObject.SetActive(true);
            return item;
        }
        
        return Instantiate(_itemPrefab, _content);
    }
    
    private void RecycleItem(TView item)
    {
        item.gameObject.SetActive(false);
        _recycledItems.Enqueue(item);
    }
    
    private void PositionItem(TView item, int index)
    {
        var rect = item.GetComponent<RectTransform>();
        rect.anchoredPosition = new Vector2(0, -index * _itemHeight);
        item.gameObject.name = $"Item_{index}";
    }
    
    private bool IsItemVisible(int index)
    {
        return _visibleItems.Any(v => GetItemIndex(v) == index);
    }
    
    private int GetItemIndex(TView item)
    {
        var rect = item.GetComponent<RectTransform>();
        return Mathf.RoundToInt(-rect.anchoredPosition.y / _itemHeight);
    }
}

Usage Example

public class InventoryScreen : MonoBehaviour
{
    [SerializeField] private VirtualizedList<ItemData, InventorySlot> _list;
    
    public void ShowInventory(List<ItemData> items)
    {
        _list.Initialize(items, BindSlot);
    }
    
    private void BindSlot(InventorySlot slot, ItemData data)
    {
        slot.SetIcon(data.Icon);
        slot.SetName(data.Name);
        slot.SetQuantity(data.Quantity);
        slot.OnClick = () => OnItemClicked(data);
    }
}

Safe Text Updates

Cached Text Component

public class SafeText : MonoBehaviour
{
    private TMP_Text _text;
    private string _lastValue;
    
    private void Awake()
    {
        _text = GetComponent<TMP_Text>();
        _lastValue = _text.text;
    }
    
    // Only update if value changed
    public void SetText(string value)
    {
        if (_lastValue != value)
        {
            _text.text = value;
            _lastValue = value;
        }
    }
    
    public void SetTextFormat(string format, params object[] args)
    {
        var value = string.Format(format, args);
        SetText(value);
    }
}

Zero-Allocation Number Display

public class NumberDisplay : MonoBehaviour
{
    private TMP_Text _text;
    private int _lastValue = int.MinValue;
    private readonly char[] _buffer = new char[16];
    
    private void Awake()
    {
        _text = GetComponent<TMP_Text>();
    }
    
    public void SetValue(int value)
    {
        if (value == _lastValue) return;
        _lastValue = value;
        
        // Zero-allocation int to string
        int length = IntToChars(value, _buffer);
        _text.SetCharArray(_buffer, 0, length);
    }
    
    private int IntToChars(int value, char[] buffer)
    {
        if (value == 0)
        {
            buffer[0] = '0';
            return 1;
        }
        
        bool negative = value < 0;
        if (negative) value = -value;
        
        int index = buffer.Length;
        
        while (value > 0)
        {
            buffer[--index] = (char)('0' + value % 10);
            value /= 10;
        }
        
        if (negative)
        {
            buffer[--index] = '-';
        }
        
        int length = buffer.Length - index;
        Array.Copy(buffer, index, buffer, 0, length);
        return length;
    }
}

Layout Optimization

Manual Layout

public class OptimizedGrid : MonoBehaviour
{
    [SerializeField] private int _columns = 4;
    [SerializeField] private float _cellWidth = 100f;
    [SerializeField] private float _cellHeight = 100f;
    [SerializeField] private float _spacing = 10f;
    
    private RectTransform _rect;
    
    private void Awake()
    {
        _rect = GetComponent<RectTransform>();
    }
    
    // Call once after adding/removing children
    public void RefreshLayout()
    {
        int index = 0;
        
        foreach (Transform child in transform)
        {
            if (!child.gameObject.activeSelf) continue;
            
            int row = index / _columns;
            int col = index % _columns;
            
            var childRect = child.GetComponent<RectTransform>();
            childRect.anchoredPosition = new Vector2(
                col * (_cellWidth + _spacing),
                -row * (_cellHeight + _spacing)
            );
            childRect.sizeDelta = new Vector2(_cellWidth, _cellHeight);
            
            index++;
        }
        
        // Update content size
        int totalRows = Mathf.CeilToInt((float)index / _columns);
        _rect.sizeDelta = new Vector2(
            _rect.sizeDelta.x,
            totalRows * (_cellHeight + _spacing)
        );
    }
}

Disable Auto Layout

public class LayoutDisabler : MonoBehaviour
{
    private LayoutGroup _layout;
    private ContentSizeFitter _sizeFitter;
    
    private void Start()
    {
        _layout = GetComponent<LayoutGroup>();
        _sizeFitter = GetComponent<ContentSizeFitter>();
        
        // Disable after initial layout
        StartCoroutine(DisableAfterFrame());
    }
    
    private IEnumerator DisableAfterFrame()
    {
        yield return null;
        
        if (_sizeFitter != null)
            _sizeFitter.enabled = false;
            
        if (_layout != null)
            _layout.enabled = false;
    }
    
    public void ForceRefresh()
    {
        if (_layout != null)
        {
            _layout.enabled = true;
            LayoutRebuilder.ForceRebuildLayoutImmediate(GetComponent<RectTransform>());
            _layout.enabled = false;
        }
    }
}

Modal Dialog System

Dialog Manager

public class DialogManager : MonoBehaviour
{
    public static DialogManager Instance { get; private set; }
    
    [SerializeField] private Canvas _dialogCanvas;
    [SerializeField] private GameObject _backdrop;
    
    private readonly Stack<UIPanel> _dialogStack = new();
    
    private void Awake()
    {
        Instance = this;
    }
    
    public async UniTask<T> ShowDialog<T>(UIPanel dialogPrefab) where T : UIPanel
    {
        var dialog = Instantiate(dialogPrefab, _dialogCanvas.transform);
        _dialogStack.Push(dialog);
        
        UpdateBackdrop();
        await dialog.FadeIn(0.2f);
        
        return (T)dialog;
    }
    
    public async UniTask CloseTopDialog()
    {
        if (_dialogStack.Count == 0) return;
        
        var dialog = _dialogStack.Pop();
        await dialog.FadeOut(0.15f);
        Destroy(dialog.gameObject);
        
        UpdateBackdrop();
    }
    
    public async UniTask CloseAllDialogs()
    {
        while (_dialogStack.Count > 0)
        {
            var dialog = _dialogStack.Pop();
            Destroy(dialog.gameObject);
        }
        
        UpdateBackdrop();
    }
    
    private void UpdateBackdrop()
    {
        _backdrop.SetActive(_dialogStack.Count > 0);
    }
}

Best Practices

1. Split canvases by update frequency
2. Disable Raycast Target on non-interactive elements
3. Use CanvasGroup for visibility, not SetActive
4. Virtualize long lists - Only render visible items
5. Avoid Layout Groups in dynamic content
6. Cache text components and avoid redundant updates
7. Pool UI elements - Don't instantiate frequently
8. Use sprite atlases for UI images
9. Avoid transparency overdraw - Minimize overlapping alpha
10. Profile with Frame Debugger - Check batch counts

Troubleshooting

Issue	Solution
High SetPass calls	Use sprite atlases
Canvas rebuild every frame	Split canvases, check hierarchy
Scroll stuttering	Virtualize list
Touch unresponsive	Check Raycast Target, Canvas order
Layout jitter	Disable auto layout, use manual
Memory from UI	Pool elements, unload unused atlases