particles/Main.cs

using System;
using System.Collections.Generic;
using System.Linq;
using System.Threading.Tasks;
using Godot;
using Particles;

public class Main : Node2D
{

    private ParticleSimulation _particleSimulation;
    private Node2D _particleNodes;
    public override void _Ready()
    {
        _particleNodes = GetNode<Node2D>("ParticlesNodes");
        GD.Randomize();
        _particleSimulation = new ParticleSimulation
        {
            ScreenSize = GetViewportRect().Size
        };
        _particleSimulation.Initialize();
        foreach (var id in _particleSimulation.LastParticlesAdded)
        {
            CreateParticleNode(id);
        }
    }

    public override void _Process(float delta)
    {
        if (Input.IsActionJustPressed("quit")) GetTree().Quit();
        if (Input.IsActionJustPressed("reset")) GetTree().ReloadCurrentScene();
    }

    public override void _PhysicsProcess(float delta)
    {
        _particleSimulation.Update();
        foreach (var id in _particleSimulation.LastParticlesRemoved)
        {
            var particleNode = _particleNodes.GetNode<ParticleNode>(id.ToString());
            particleNode.Free();
        }
        foreach (var id in _particleSimulation.LastParticlesAdded)
        {
            CreateParticleNode(id);
        }

        var particleNodes = _particleNodes.GetChildren();
        foreach (ParticleNode particleNode in particleNodes)
        {
            var simulationParticle = _particleSimulation.GetParticle(particleNode.SimulationId);
            particleNode.Position = simulationParticle.Position;
            particleNode.SetColor(simulationParticle.Type.Hue, simulationParticle.Health);
        }
    }

    private void CreateParticleNode(int id)
    {
        var particleScene = GD.Load<PackedScene>("res://ParticleNode.tscn");
        var particleNode = particleScene.Instance<ParticleNode>();
        particleNode.Name = id.ToString();
        particleNode.SimulationId = id;
        _particleNodes.AddChild(particleNode);
    }
}