particles/ParticleSimulation/ParticleSimulation.cs

#define MULTITHREADED

using System.Collections.Generic;
using System.Linq;
using Godot;
#if MULTITHREADED
    using System.Threading.Tasks;
#endif

namespace Particles.ParticleSimulation
{
    public class ParticleSimulation
    {
        // size of simulation space
        public Vector2 SpaceSize;
        
        // dictionary of particles with particle Id being the key
        private readonly Dictionary<int, Particle> _particles = new Dictionary<int, Particle>();
        
        private readonly List<ParticleType> _particleTypes = new List<ParticleType>();
        
        // task list if multi-threaded
        #if MULTITHREADED
            private readonly List<Task> _tasks = new List<Task>();
        #endif
        
        // updated on every simulation update
        public List<int> LastParticlesAdded { get; private set; } = new List<int>();
        public List<int> LastParticlesRemoved { get; private set; } = new List<int>();

        // counts up for each particle added
        private int _idCount;
        
        private const int MaxParticles = 1100;
        private const int MaxParticleTypes = 10;
        
        private const float HealthDelta = 0.005f;
        private const float NegativeHealthMultiplier = 2f;
        private const float PositiveHealthMultiplier = 4f;

        private const float ParticleCollisionRadius = 20f;

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

        public void Update()
        {
            LastParticlesRemoved.Clear();
            LastParticlesAdded.Clear();
            
            // update all particles
            #if MULTITHREADED
                _tasks.Clear();
                foreach (var id in _particles.Keys)
                    _tasks.Add(Task.Factory.StartNew(UpdateParticle, id));
                Task.WaitAll(_tasks.ToArray());
            #else
            foreach (var id in _particles.Keys)
                UpdateParticle(id);
            #endif
            
            // used to ensure only one particle is moved per update
            var movedParticle = false;
            
            foreach (var particle in _particles.Select(p => p.Value))
            {
                particle.WasTeleportedLast = false;
                if (movedParticle == false && particle.Health == 0f)
                {
                    if (GD.Randf() < 0.1f)
                    {
                        particle.Position = GetRandomParticlePosition();
                        particle.WasTeleportedLast = true;
                        particle.Health = 1f;
                        movedParticle = true;
                        continue;
                    }
                }
                var position = particle.Position;
                particle.Velocity = particle.Velocity.Clamped(5f);
                position += particle.Velocity;
                particle.Velocity *= 0.855f;    // friction
                if (position.x > SpaceSize.x)
                {
                    position.x -= SpaceSize.x;
                    particle.WasTeleportedLast = true;
                }
                else if (position.x < 0)
                {
                    position.x += SpaceSize.x;
                    particle.WasTeleportedLast = true;
                }

                if (position.y > SpaceSize.y)
                {
                    position.y -= SpaceSize.y;
                    particle.WasTeleportedLast = true;
                }
                else if (position.y < 0)
                {
                    position.y += SpaceSize.y;
                    particle.WasTeleportedLast = true;
                }
                /*
                particle.AddAverageSpeedValue(particle.Velocity.Length());
                
                if (particle.AverageSpeed < 0.5f)
                    particle.Health -= HealthDelta * NegativeHealthMultiplier;
                else
                    particle.Health += HealthDelta * PositiveHealthMultiplier;
                
                if (movedParticle == false && particle.Health == 0f)
                {
                    if (GD.Randf() < 0.1f)
                    {
                        particle.Position = GetRandomParticlePosition();
                        particle.ResetAverageSpeed();
                        particle.WasTeleportedLast = true;
                        particle.Health = 1f;
                        movedParticle = true;
                        continue;
                    }
                }
                */
                particle.Position = position;
            }

            // ReSharper disable once InvertIf
            if (_particles.Count < MaxParticles)
            {
                for (var i = 0; i < 3 && _particles.Count < MaxParticles; i++)
                    CreateRandomParticle();
            }
        }

        // ReSharper disable once UnusedMember.Local
        private void RemoveParticleType(ParticleType type)
        {
            _particleTypes.Remove(type);
            foreach (var t in _particleTypes)
            {
                t.RemoveRelationship(type);
            }
        }

        // ReSharper disable once UnusedMember.Local
        private void RemoveParticle(int id)
        {
            _particles.Remove(id);
            LastParticlesRemoved.Add(id);
        }

        private void CreateRandomParticleType()
        {
            var type = new ParticleType()
            {
                Hue = (float) GD.RandRange(0, 1)
            };
            _particleTypes.Add(type);
            foreach (var type1 in _particleTypes)
            foreach (var type2 in _particleTypes)
                type1.AddRelationship(type2,
                    new ParticleRelationshipProps(ParticleCollisionRadius, (float) GD.RandRange(25, 55), 
                    (float)GD.RandRange(-0.675, 0.7)));
        }

        private void CreateRandomParticle()
        {
            var randomIndex = (int) (GD.Randi() % _particleTypes.Count);
            var type = _particleTypes[randomIndex];
            CreateParticle(type, (GetRandomParticlePosition() / 50f) + (SpaceSize / 2f));
        }

        private void CreateParticle(ParticleType type, Vector2 position)
        {
            var particle = new Particle(_idCount, type)
            {
                Position = position,
                Health = 1f
            };
            LastParticlesAdded.Add(_idCount);
            _particles.Add(_idCount, particle);
            _idCount++;
        }

        private Vector2 GetRandomParticlePosition()
        {
            var position = new Vector2(
                (float) GD.RandRange(0, SpaceSize.x),
                (float) GD.RandRange(0, SpaceSize.y));
            return position;
        }
        
        private Vector2 GetScreenWrapPosition(Vector2 p1, Vector2 p2)
        {
            var newPosition = p2;
            if (p2.x > (p1.x + (SpaceSize.x / 2f)))
                newPosition.x = p2.x - SpaceSize.x;
            else if (p2.x < (p1.x - (SpaceSize.x / 2f)))
                newPosition.x = p2.x + SpaceSize.x;
            if (p2.y > (p1.y + (SpaceSize.y / 2f)))
                newPosition.y = p2.y - SpaceSize.y;
            else if (p2.y < (p1.y - (SpaceSize.y / 2f)))
                newPosition.y = p2.y + SpaceSize.y;
            return newPosition;
        }
        
        public Particle GetParticle(int id)
        {
            return _particles[id];
        }
        
        private void 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 > (55f * 55f))
                    continue;

                if (distanceSquared < (35f * 35f))
                    closeCount++;
                
                // collision force
                float distance;
                Vector2 direction;
                
                if (distanceSquared < (ParticleCollisionRadius * ParticleCollisionRadius))
                {
                    direction = particle1.Position.DirectionTo(position);
                    distance = particle1.Position.DistanceTo(position);
                    var collisionForce = 1f / (0.35f + Mathf.Pow(Mathf.E, -1.15f * (distance - 12f))) - 1f / 0.35f;
                    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)
                {
                    direction = particle1.Position.DirectionTo(position);
                    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 > 70)
                particle1.Health -= HealthDelta * NegativeHealthMultiplier;
            else
                particle1.Health += HealthDelta * PositiveHealthMultiplier;
        }
    }
}