SelectionDetectSystem.cs

using System;
using Leopotam.EcsLite;
using Microsoft.Xna.Framework;
using Microsoft.Xna.Framework.Input;

public class SelectionDetectSystem : IEcsRunSystem, IEcsInitSystem
{
    private EcsWorld _world;
    private EcsFilter _gameObjectFilter;
    private EcsPool<SelectionBox> _selectionPool;
    private EcsPool<GameObject> _gameObjectPool;
    private EcsPool<Selected> _selectedPool;
    private EcsPool<Bounds> _boundsPool;
    private EcsPool<ColorComponent> _colorPool;
    private EcsFilter _selectionFilter;
    
    private SelectionInputSystem _selectionInputSystem;
    private bool _previousIsActive;
    // Сохраняем конструктор, как просили
    public SelectionDetectSystem(EcsWorld world, SelectionInputSystem selectionInputSystem)
    {
        _world = world;
        _selectionInputSystem = selectionInputSystem;
    }

    public void Init(IEcsSystems systems)
    {
        // Инициализируем пулы и фильтры
        _gameObjectFilter = _world.Filter<GameObject>().End();
        _selectionPool = _world.GetPool<SelectionBox>();
        _gameObjectPool = _world.GetPool<GameObject>();
        _selectedPool = _world.GetPool<Selected>();
        _boundsPool = _world.GetPool<Bounds>();
        _colorPool = _world.GetPool<ColorComponent>();
        _selectionFilter = _world.Filter<SelectionBox>().End();

        _selectionInputSystem.startSelect += ClearStartSelect;
    }

    public void Run(IEcsSystems systems)
    {
        MouseState currentMouseState = Mouse.GetState();
        Vector2 mousePosition = new Vector2(currentMouseState.X, currentMouseState.Y);

        foreach (int selectionEntity in _selectionFilter)
        {
            if (!_selectionPool.Has(selectionEntity)) continue;

            ref SelectionBox selection = ref _selectionPool.Get(selectionEntity);

            if(!selection.IsActive) continue;
            ClearStartSelect();
            // Проверяем пересечения
            foreach (int entity in _gameObjectFilter)
            {
                if (!_gameObjectPool.Has(entity) || !_boundsPool.Has(entity) || !_colorPool.Has(entity)) continue;

                ref GameObject gameObject = ref _gameObjectPool.Get(entity);
                ref Bounds bounds = ref _boundsPool.Get(entity);
                ref ColorComponent color = ref _colorPool.Get(entity);
                
                if (selection.Bounds.Intersects(bounds.Rectangle))
                {
                    if (!_selectedPool.Has(entity))
                    {
                        ref Selected selected = ref _selectedPool.Add(entity);
                        color.Value = Color.Blue;  

                    }
                }
            }

                _previousIsActive = selection.IsActive;
        }
    }

    public void ClearStartSelect()
    {
        _selectedPool = _world.GetPool<Selected>();
        foreach (int selectionEntity in _selectionFilter)
        {
            if (!_selectionPool.Has(selectionEntity)) continue;
            // Снимаем выделение со всех

            foreach (int entity in _gameObjectFilter)
            {
                if (_selectedPool.Has(entity))
                {
                    _selectedPool.Del(entity);
                    if (_colorPool.Has(entity))
                    {
                        ref ColorComponent color = ref _colorPool.Get(entity);
                        color.Value = Color.White;
                    }
                }
            }

            // _world.DelEntity(selectionEntity);
        }
    }
}