Engine-Pong/Game/Physics2D/Collider2DBehaviour.cs

using System;
using System.Collections.Generic;
using System.Collections.ObjectModel;
using System.Diagnostics.CodeAnalysis;

using Microsoft.Xna.Framework;

using Pong;

using Syntriax.Engine.Core;
using Syntriax.Engine.Core.Abstract;
using Syntriax.Engine.Graphics.TwoDimensional;
using Syntriax.Engine.Physics2D.Abstract;

namespace Syntriax.Engine.Physics2D;


public class Collider2DBehaviour(IList<Vector2> vertices) : BehaviourOverride, ICollider2D
{
    private List<Triangle> triangles = new List<Triangle>(32);
    private readonly List<Vector2> _vertices = new List<Vector2>(32);
    private IRigidBody2D? _rigidBody2D = null;

    public Action<IAssignableTransform>? OnTransformAssigned { get => GameObject.OnTransformAssigned; set => GameObject.OnTransformAssigned = value; }
    public Action<ICollider2D, ICollider2D>? OnCollision { get; set; } = null;


    private IList<Vector2> verticesOriginal { get; } = vertices;

    public Vector2 OffsetPosition { get; set; } = Vector2.Zero;
    public Vector2 OffsetScale { get; set; } = Vector2.One;
    public float OffsetRotation { get; set; } = 0f;

    ITransform IAssignableTransform.Transform => Transform;
    public IReadOnlyList<Vector2> Vertices => _vertices;

    public IRigidBody2D? RigidBody2D
    {
        get
        {
            if (_rigidBody2D is null)
                BehaviourController.TryGetBehaviour(out _rigidBody2D);

            return _rigidBody2D;
        }
    }

    public bool Assign(ITransform transform) => GameObject.Assign(transform);

    public bool CheckCollision(Vector2 point, ICollider2D otherCollider, out CollisionInformation collisionInformation)
    {
        collisionInformation = new CollisionInformation(Vector2.Zero, Vector2.Zero);

        foreach (var triangle in triangles)
        {
            if (!PhysicsMath.IsInTriangle(point, triangle))
                continue;

            OnCollision?.Invoke(this, otherCollider);

            Line main = new(otherCollider.Transform.Position, point);

            foreach (var line in PhysicsMath.GetLines([triangle.A, triangle.B, triangle.C]))
            {
                if (!PhysicsMath.DoIntersect(main, line))
                    continue;

                Vector2 contactPoint = PhysicsMath.ClosestPointOnLine(point, line);

                Vector2 normal = contactPoint - point;
                if (normal.LengthSquared() < 0.001f)
                    normal = new Vector2(0f, 1f);

                normal.Normalize();

                collisionInformation = new CollisionInformation(normal, contactPoint);
                break;
            }
            return true;
        }

        return false;
    }

    public void RecalculateVertices()
    {
        triangles.Clear();

        _vertices.Clear();
        foreach (var vertex in verticesOriginal)
        {
            Vector2 scaledPosition = new Vector2(vertex.X * Transform.Scale.X * OffsetScale.X, vertex.Y * Transform.Scale.Y * OffsetScale.Y);
            _vertices.Add(scaledPosition + Transform.Position);
        }

        Triangle superTriangle = PhysicsMath.GetSuperTriangle(_vertices);
        triangles.Add(superTriangle);

        List<Triangle> badTriangles = new(32);
        List<Line> polygon = new(32);

        foreach (var vertex in _vertices)
        {
            badTriangles.Clear();
            polygon.Clear();

            foreach (var triangle in triangles)
            {
                Circle circle = PhysicsMath.GetCircumCircle(triangle);
                if (Vector2.DistanceSquared(circle.Center, vertex) <= circle.Radius * circle.Radius)
                    badTriangles.Add(triangle);
            }

            foreach (var triangle in badTriangles)
                foreach (var line in PhysicsMath.GetLines([triangle.A, triangle.B, triangle.C]))
                    if (PhysicsMath.DoesLineExistInVertices(line, [triangle.A, triangle.B, triangle.C]))
                        polygon.Add(line);

            foreach (var triangle in badTriangles)
                triangles.Remove(triangle);

            foreach (var line in polygon)
                triangles.Add(new(line.From, line.To, vertex));
        }

        for (int i = triangles.Count - 1; i >= 0; i--)
        {
            Triangle triangle = triangles[i];
            if (
                triangle.A == superTriangle.A || triangle.A == superTriangle.B || triangle.A == superTriangle.C ||
                triangle.B == superTriangle.A || triangle.B == superTriangle.B || triangle.B == superTriangle.C ||
                triangle.C == superTriangle.A || triangle.C == superTriangle.B || triangle.C == superTriangle.C
            )
                triangles.RemoveAt(i);
        }

        for (int i = gameObjects.Count - 1; i >= 0; i--)
        {
            IGameObject gameObject = gameObjects[i];
            Game1.gameManager.RemoveGameObject(gameObject);
            gameObjects.RemoveAt(i);
        }


        for (int i = 0; i < triangles.Count; i++)
        {
            Triangle triangle = triangles[i];
            foreach (var line in PhysicsMath.GetLines([triangle.A, triangle.B, triangle.C]))
            {
                GameObject gameObject = Game1.gameManager.InstantiateGameObject<GameObject>();
                DisplayableSpriteBehaviour displayableSpriteBehaviour = gameObject.BehaviourController.AddBehaviour<DisplayableSpriteBehaviour>();
                displayableSpriteBehaviour.Color = Color.Aqua;
                displayableSpriteBehaviour.Origin = new(0.5f, 1f);
                displayableSpriteBehaviour.Assign(Game1.spriteBox);
                gameObject.Transform.Position = line.From;
                Vector2 vector2 = line.To - line.From;
                gameObject.Transform.Scale = new Vector2(2f, .0f) + Vector2.UnitY * vector2.Length();
                gameObject.Transform.Rotation = (float)Math.Atan2(vector2.X, vector2.Y);
                gameObjects.Add(gameObject);

                gameObject = Game1.gameManager.InstantiateGameObject<GameObject>();
                displayableSpriteBehaviour = gameObject.BehaviourController.AddBehaviour<DisplayableSpriteBehaviour>();
                displayableSpriteBehaviour.Color = Color.Crimson;
                displayableSpriteBehaviour.Assign(Game1.spriteBox);
                gameObject.Transform.Position = line.To;
                gameObject.Transform.Scale = new Vector2(4f, 4f);
                gameObjects.Add(gameObject);
            }
        }

        foreach (var vertex in Vertices)
        {
            GameObject gameObject = Game1.gameManager.InstantiateGameObject<GameObject>();
            DisplayableSpriteBehaviour displayableSpriteBehaviour = gameObject.BehaviourController.AddBehaviour<DisplayableSpriteBehaviour>();
            displayableSpriteBehaviour.Color = Color.GreenYellow;
            displayableSpriteBehaviour.Assign(Game1.spriteBox);
            gameObject.Transform.Position = vertex;
            gameObject.Transform.Scale = new Vector2(2f, 2f);
            gameObjects.Add(gameObject);
        }
    }

    private List<IGameObject> gameObjects = new List<IGameObject>(32);

}