particles/ParticleSimulation/ParticleSimulation.cs

using System;
using Godot;
using System.Collections.Generic;
using System.ComponentModel;
using System.Threading.Tasks;

namespace Particles
{
    public class ParticleSimulation
    {

        public Vector2 ScreenSize;
        
        private Dictionary<int, Particle> _particles = new Dictionary<int, Particle>();
        
        private List<ParticleType> _particleTypes = new List<ParticleType>();
        private Dictionary<ParticleType, int> _particleTypeCounts = new Dictionary<ParticleType, int>();
        private List<Task> tasks = new List<Task>();

        public List<int> LastParticlesAdded { get; private set; } = new List<int>();
        public List<int> LastParticlesRemoved { get; private set; } = new List<int>();

        private int _idCount = 0;
        
        private const int MaxParticles = 1000;
        private const int MaxParticleTypes = 10;
        private const float HealthDelta = 0.002f;
        private const float NegativeHealthMultiplier = 1.5f;

        private const float ParticleCollisionRadius = 13f;
        private const float ParticleCollisionStrength = 2.5f;
        private const float ParticleCollisionResponse = 2f;

        public void Initialize()
        {
            for (var i = 0; i < MaxParticleTypes; i++)
                CreateRandomParticleType();
            for (var i = 0; i < MaxParticles; i++)
                CreateRandomParticle();
        }

        public void Update()
        {
            LastParticlesRemoved.Clear();
            LastParticlesAdded.Clear();
            tasks.Clear();
            foreach (var id in _particles.Keys)
                tasks.Add(Task.Factory.StartNew(UpdateParticle, id));
            Task.WaitAll(tasks.ToArray());
            var deletedParticle = false;
            foreach (var p in _particles)
            {
                var particle = p.Value;
                if (deletedParticle == false && particle.Health == 0f)
                {
                    if (GD.Randf() < 0.2f)
                    {
                        LastParticlesRemoved.Add(p.Key);
                        deletedParticle = true;
                        continue;
                    }
                }

                var position = particle.Position;
                particle.Velocity = particle.Velocity.Clamped(4f);
                position += particle.Velocity;
                particle.Velocity *= 0.875f;    // friction
                if (position.x > ScreenSize.x)
                    position.x -= ScreenSize.x;
                else if (position.x < 0)
                    position.x += ScreenSize.x;
                if (position.y > ScreenSize.y)
                    position.y -= ScreenSize.y;
                else if (position.y < 0)
                    position.y += ScreenSize.y;
                particle.AddAverageSpeedValue(particle.Position.DistanceTo(position));
                
                if (particle.AverageSpeed < 0.15f)
                    particle.Health -= HealthDelta * NegativeHealthMultiplier;
                else
                    particle.Health += HealthDelta;

                if (deletedParticle == false && particle.Health == 0f)
                {
                    if (GD.Randf() < 0.2f)
                    {
                        LastParticlesRemoved.Add(p.Key);
                        deletedParticle = true;
                        continue;
                    }
                }

                particle.Position = position;
            }

            foreach (var id in LastParticlesRemoved)
            {
                _particles.Remove(id);
            }
            
            if (_particles.Count < MaxParticles)
            {
                if (GD.Randf() < 0.3f)
                {
                    CreateRandomParticle();
                }
            }
        }

        private void RemoveParticleType(ParticleType type)
        {
            _particleTypes.Remove(type);
            foreach (var t in _particleTypes)
            {
                t.RemoveRelationship(type);
            }
        }

        private void CreateRandomParticleType()
        {
            var type = new ParticleType()
            {
                Hue = (float) GD.RandRange(0, 1)
            };
            _particleTypes.Add(type);
            _particleTypeCounts[type] = 0;
            foreach (var type1 in _particleTypes)
                foreach(var type2 in _particleTypes)
                    type1.AddRelationship(type2,
                        new ParticleRelationshipProps(ParticleCollisionRadius, (float)GD.RandRange(22, 50),
                            (float)GD.RandRange(-0.3, 0.3)));
        }

        private void CreateRandomParticle()
        {
            var randomIndex = (int) (GD.Randi() % _particleTypes.Count);
            var type = _particleTypes[randomIndex];
            CreateParticle(type);
        }

        private void CreateParticle(ParticleType type)
        {
            var particle = new Particle(_idCount, type)
            {
                Position = GetRandomParticlePosition(),
                Health = 1f
            };
            LastParticlesAdded.Add(_idCount);
            _particles.Add(_idCount, particle);
            _idCount++;
            _particleTypeCounts[type]++;
        }

        private Vector2 GetRandomParticlePosition()
        {
            var position = new Vector2(
                (float) GD.RandRange(0, ScreenSize.x),
                (float) GD.RandRange(0, ScreenSize.y));
            return position;
        }
        
        private Vector2 GetScreenWrapPosition(Vector2 p1, Vector2 p2)
        {
            var newPosition = p2;
            if (p2.x > (p1.x + (ScreenSize.x / 2f)))
                newPosition.x = p2.x - ScreenSize.x;
            else if (p2.x < (p1.x - (ScreenSize.x / 2f)))
                newPosition.x = p2.x + ScreenSize.x;
            if (p2.y > (p1.y + (ScreenSize.y / 2f)))
                newPosition.y = p2.y - ScreenSize.y;
            else if (p2.y < (p1.y - (ScreenSize.y / 2f)))
                newPosition.y = p2.y + ScreenSize.y;
            return newPosition;
        }
        
        public Particle GetParticle(int id)
        {
            return _particles[id];
        }
        
        private Task UpdateParticle(object i)
        {
            var id = (int)i;
            var particle1 = _particles[id];
            var closeCount = 0;
            foreach (var p2 in _particles)
            {
                var particle2 = p2.Value;
                if (particle1 == particle2)
                    continue;
                var position = GetScreenWrapPosition(particle1.Position, particle2.Position);
                var distanceSquared = particle1.Position.DistanceSquaredTo(position);
                if (distanceSquared > (50f * 50f))
                    continue;
                var direction = particle1.Position.DirectionTo(position);

                if (distanceSquared < (50f * 50f))
                    closeCount++;
                
                // collision force
                float distance;
                if (distanceSquared < (ParticleCollisionRadius * ParticleCollisionRadius))
                {
                    distance = particle1.Position.DistanceTo(position);
                    var collisionForce = 1f / ((1f / ParticleCollisionStrength) + Mathf.Pow(Mathf.E, -ParticleCollisionResponse * (distance - ParticleCollisionRadius + 3f))) - 1f / (1f / ParticleCollisionStrength);
                    //var collisionForce = 1f / (0.6f + Mathf.Pow(Mathf.E, -(distance - ParticleCollisionRadius - 2f))) - 1f / 0.6f;
                    particle1.Velocity += direction * collisionForce;
                }
                
                // particle relationship force
                var props = particle1.Type.GetRelationship(particle2.Type);
                if (props.Force != 0f && distanceSquared >= props.MinRadius * props.MinRadius &&
                    distanceSquared <= props.MaxRadius * props.MaxRadius)
                {
                    distance = particle1.Position.DistanceTo(position);
                    var mid = (props.MinRadius + props.MaxRadius) / 2f;
                    float particleForce;
                    if (props.Force > 0)
                    {
                        if (distance <= mid)
                        {
                            particleForce = 1f / ((1f / props.Force) + Mathf.Pow(Mathf.E, -4 * (distance - props.MinRadius - 1f)));
                        }
                        else
                        {
                            particleForce = 1f / ((1f / props.Force) + Mathf.Pow(Mathf.E, 4 * (distance - props.MaxRadius + 1f)));
                        }
                    }
                    else
                    {
                        if (distance <= mid)
                        {
                            particleForce = -1f / ((-1f / props.Force) + Mathf.Pow(Mathf.E, -4 * (distance - props.MinRadius - 1f)));
                        }
                        else
                        {
                            particleForce = -1f / ((-1f / props.Force) + Mathf.Pow(Mathf.E, 4 * (distance - props.MaxRadius + 1f)));
                        }
                    }
                    
                    
                    particle1.Velocity += direction * particleForce;
                }
            }
            
            if (closeCount < 4 || closeCount > 33)
                particle1.Health -= HealthDelta * NegativeHealthMultiplier;
            else
                particle1.Health += HealthDelta;
            
            return Task.CompletedTask;
        }
    }
}