SelectionRenderSystem.cs

using Leopotam.EcsLite;
using Microsoft.Xna.Framework;
using Microsoft.Xna.Framework.Graphics;

public class SelectionRenderSystem : IEcsRunSystem
{
    private EcsWorld _world;
    private EcsFilter _selectionFilter;
    private SpriteBatch _spriteBatch;
    private Texture2D _pixelTexture;  // 1x1 пиксель для рисования прямоугольника

    private Camera _camera;
    public SelectionRenderSystem(EcsWorld world, GraphicsDevice graphicsDevice, SpriteBatch spriteBatch, Camera camera)
    {
        _world = world;
        _spriteBatch = spriteBatch;
        _camera = camera;
        _selectionFilter = _world.Filter<SelectionBox>().End();

        // Создаём 1x1 текстуру для заливки
        _pixelTexture = new Texture2D(graphicsDevice, 1, 1);
        _pixelTexture.SetData(new[] { Color.White });
    }

    public void Run(IEcsSystems systems)
    {
        foreach (int entity in _selectionFilter)
        {
            ref SelectionBox selection = ref _world.GetPool<SelectionBox>().Get(entity);
            if (!selection.IsActive) continue;

            Rectangle bounds = selection.Bounds;

            // Рисуем прозрачный прямоугольник (заливка)
            _spriteBatch.Draw(
                _pixelTexture,
                bounds,
                new Color(0, 0, 0, 100)  // Полупрозрачный зелёный (можно настроить)
            );

            // Рисуем рамку (толщиной 2 пикселя)
            int borderThickness = (int)MathHelper.Clamp((int)(2 / _camera.Zoom), 1, 5f);
            
            // Верхняя линия
            _spriteBatch.Draw(_pixelTexture, new Rectangle(bounds.X, bounds.Y, bounds.Width, borderThickness), Color.Green);
            // Нижняя линия
            _spriteBatch.Draw(_pixelTexture, new Rectangle(bounds.X, bounds.Y + bounds.Height - borderThickness, bounds.Width, borderThickness), Color.Green);
            // Левая линия
            _spriteBatch.Draw(_pixelTexture, new Rectangle(bounds.X, bounds.Y, borderThickness, bounds.Height), Color.Green);
            // Правая линия
            _spriteBatch.Draw(_pixelTexture, new Rectangle(bounds.X + bounds.Width - borderThickness, bounds.Y, borderThickness, bounds.Height), Color.Green);
        }
    }
}