Unity SpriteAtlas 优化与实践

┌──────────────────────────────────────────────────────────────┐
│  单独纹理渲染                    图集渲染                      │
│                                                                │
│   [Sprite A] → Draw Call 1       ┌─────────────┐              │
│   [Sprite B] → Draw Call 2       │  A │ B │ C  │              │
│   [Sprite C] → Draw Call 3  →    │────┼───┼────│ → Draw Call 1│
│   [Sprite D] → Draw Call 4       │  D │ E │ F  │              │
│   [Sprite E] → Draw Call 5       └─────────────┘              │
│   [Sprite F] → Draw Call 6                                    │
│                                                                │
│   6 Draw Calls                   1 Draw Call                  │
└──────────────────────────────────────────────────────────────┘

/// <summary>
/// 图集管理配置 - 用于 Luban 配置表
/// {"atlasName":"Atlas_Hero_001","loadPolicy":"OnDemand","priority":2,"maxSize":2048}
/// </summary>
[Serializable]
public class SpriteAtlasConfig
{
    /// <summary>
    /// 图集资源名称 (不含路径和后缀)
    /// 示例: "Atlas_UI_Common"
    /// </summary>
    public string atlasName;

    /// <summary>
    /// 加载策略
    /// Preload: 游戏启动时加载
    /// OnDemand: 首次使用时加载
    /// SceneBound: 随场景加载/卸载
    /// </summary>
    public AtlasLoadPolicy loadPolicy;

    /// <summary>
    /// 加载优先级，数值越大越优先
    /// 默认值: 0
    /// </summary>
    public int priority;

    /// <summary>
    /// 图集最大尺寸限制
    /// 默认值: 2048
    /// </summary>
    public int maxSize;
}

public enum AtlasLoadPolicy
{
    Preload,    // 预加载
    OnDemand,   // 按需加载
    SceneBound  // 场景绑定
}

using UnityEngine;
using UnityEngine.U2D;

/// <summary>
/// SpriteAtlas 延迟绑定管理器
/// 处理 Addressables 或 AssetBundle 中的图集加载
/// </summary>
public class SpriteAtlasLateBindingManager : MonoBehaviour
{
    private void OnEnable()
    {
        // 注册回调：当 Unity 请求一个未加载的 SpriteAtlas 时触发
        SpriteAtlasManager.atlasRequested += OnAtlasRequested;
    }

    private void OnDisable()
    {
        SpriteAtlasManager.atlasRequested -= OnAtlasRequested;
    }

    /// <summary>
    /// 图集请求回调
    /// </summary>
    /// <param name="atlasTag">被请求的图集名称 (不含路径)</param>
    /// <param name="callback">加载完成后的回调</param>
    private void OnAtlasRequested(string atlasTag, System.Action<SpriteAtlas> callback)
    {
        // 示例：从 Addressables 加载
        // var handle = Addressables.LoadAssetAsync<SpriteAtlas>(atlasTag);
        // handle.Completed += op => callback(op.Result);

        // 示例：从 Resources 加载 (仅用于测试)
        var atlas = Resources.Load<SpriteAtlas>($"Atlas/{atlasTag}");
        callback?.Invoke(atlas);
    }
}

/// <summary>
/// 根据设备分辨率选择图集 Variant
/// </summary>
public static class SpriteAtlasVariantSelector
{
    public enum QualityLevel
    {
        Low,    // 0.5x 缩放
        Medium, // 0.75x 缩放
        High    // 1.0x 原图
    }

    /// <summary>
    /// 根据屏幕高度自动选择质量等级
    /// </summary>
    public static QualityLevel GetRecommendedQuality()
    {
        int screenHeight = Screen.height;

        if (screenHeight < 720)  return QualityLevel.Low;
        if (screenHeight < 1080) return QualityLevel.Medium;
        return QualityLevel.High;
    }

    /// <summary>
    /// 获取 Variant 图集后缀
    /// </summary>
    public static string GetVariantSuffix(QualityLevel level)
    {
        return level switch
        {
            QualityLevel.Low    => "_LD",  // Low Definition
            QualityLevel.Medium => "_SD",  // Standard Definition
            QualityLevel.High   => "_HD",  // High Definition
            _ => "_SD"
        };
    }
}

┌─────────────────────────────────────────────────────────┐
│                  Vampirefall 图集架构                    │
├─────────────────────────────────────────────────────────┤
│                                                          │
│  [常驻层] ────────────────────────────────────────────  │
│     └── Atlas_UI_Common, Atlas_VFX_Common                │
│                                                          │
│  [场景层] ────────────────────────────────────────────  │
│     └── Atlas_Biome_{Forest/Desert/Ice...}               │
│     └── Atlas_Tower_{Archer/Mage/Barracks...}            │
│                                                          │
│  [动态层] ────────────────────────────────────────────  │
│     └── Atlas_Hero_{ID}  (按需加载/卸载)                 │
│     └── Atlas_Boss_{ID}  (Boss 战加载)                   │
│                                                          │
└─────────────────────────────────────────────────────────┘