Syntriax.Engine/Engine.Physics2D/CollisionDetector.cs

using System.Diagnostics.CodeAnalysis;

using Syntriax.Engine.Core;
using Syntriax.Engine.Physics2D.Abstract;
using Syntriax.Engine.Physics2D.Primitives;

namespace Syntriax.Engine.Physics2D;

public class CollisionDetector : ICollisionDetector
{
    public bool TryDetect<T1, T2>(T1 left, T2 right, [NotNullWhen(true)] out CollisionDetectionInformation? collisionInformation)
        where T1 : ICollider2D
        where T2 : ICollider2D
    {
        collisionInformation = default;
        if (left is IShapeCollider2D shapeColliderLeft)
        {
            if (right is IShapeCollider2D shapeColliderRight)
                return DetectShapeShape(shapeColliderLeft, shapeColliderRight, out collisionInformation);
            else if (right is ICircleCollider2D circleColliderRight)
                return DetectShapeCircle(shapeColliderLeft, circleColliderRight, out collisionInformation);
        }
        else if (left is ICircleCollider2D circleColliderLeft)
        {
            if (right is IShapeCollider2D shapeColliderRight)
                return DetectCircleShape(circleColliderLeft, shapeColliderRight, out collisionInformation);
            else if (right is ICircleCollider2D circleColliderRight)
                return DetectCircleCircle(circleColliderLeft, circleColliderRight, out collisionInformation);
        }

        return false;
    }

    private static bool DetectCircleShape(ICircleCollider2D circleCollider, IShapeCollider2D shapeCollider, out CollisionDetectionInformation? collisionInformation)
    {
        return DetectShapeCircle(shapeCollider, circleCollider, out collisionInformation);
    }

    private static bool DetectShapeShape(IShapeCollider2D left, IShapeCollider2D right, out CollisionDetectionInformation? collisionInformation)
    {
        collisionInformation = default;
        return DetectShapeShapeOneWay(left, right, ref collisionInformation) && DetectShapeShapeOneWay(right, left, ref collisionInformation);
    }

    private static bool DetectShapeShapeOneWay(IShapeCollider2D left, IShapeCollider2D right, ref CollisionDetectionInformation? collisionInformation)
    {
        var vertices = left.ShapeWorld.Vertices;
        int count = vertices.Count;

        for (int indexProjection = 0; indexProjection < count; indexProjection++)
        {
            Vector2D projectionVector = vertices[indexProjection].FromTo(vertices[(indexProjection + 1) % count]).Perpendicular().Normalized;

            Projection leftProjection = left.ShapeWorld.ToProjection(projectionVector);
            Projection rightProjection = right.ShapeWorld.ToProjection(projectionVector);

            if (!leftProjection.Overlaps(rightProjection, out float depth))
                return false;

            if (collisionInformation == default || Math.Abs(collisionInformation.Penetration) > Math.Abs(depth))
                collisionInformation = new(left, right, projectionVector, depth);
        }

        return true;
    }

    private static bool DetectShapeCircle(IShapeCollider2D shapeCollider, ICircleCollider2D circleCollider, out CollisionDetectionInformation? collisionInformation)
    {
        collisionInformation = default;

        {
            Vector2D shapeToCircleProjectionVector = shapeCollider.Transform.Position.FromTo(circleCollider.CircleWorld.Center).Normalized;

            Projection shapeProjection = shapeCollider.ShapeWorld.ToProjection(shapeToCircleProjectionVector);
            Projection circleProjection = circleCollider.CircleWorld.ToProjection(shapeToCircleProjectionVector);

            if (!shapeProjection.Overlaps(circleProjection, out float depth))
                return false;

            if (collisionInformation == default || Math.Abs(collisionInformation.Penetration) > Math.Abs(depth))
                collisionInformation = new(shapeCollider, circleCollider, shapeToCircleProjectionVector, depth);
        }

        var vertices = shapeCollider.ShapeWorld.Vertices;
        int count = vertices.Count;

        for (int indexProjection = 0; indexProjection < count; indexProjection++)
        {
            Vector2D projectionVector = vertices[indexProjection].FromTo(vertices[(indexProjection + 1) % count]).Perpendicular().Normalized;

            Projection shapeProjection = shapeCollider.ShapeWorld.ToProjection(projectionVector);
            Projection circleProjection = circleCollider.CircleWorld.ToProjection(projectionVector);

            if (!shapeProjection.Overlaps(circleProjection, out float depth))
                return false;

            if (collisionInformation == default || Math.Abs(collisionInformation.Penetration) > Math.Abs(depth))
                collisionInformation = new(shapeCollider, circleCollider, projectionVector, depth);
        }

        return true;
    }

    private static bool DetectCircleCircle(ICircleCollider2D left, ICircleCollider2D right, out CollisionDetectionInformation? collisionInformation)
    {
        collisionInformation = default;

        Vector2D leftToRightCenterProjectionVector = left.CircleWorld.Center.FromTo(right.CircleWorld.Center).Normalized;

        Projection leftProjection = left.CircleWorld.ToProjection(leftToRightCenterProjectionVector);
        Projection rightProjection = right.CircleWorld.ToProjection(leftToRightCenterProjectionVector);

        bool collision = leftProjection.Overlaps(rightProjection, out float depth);

        if (collision)
            collisionInformation = new(left, right, leftToRightCenterProjectionVector, depth);

        return collision;
    }

    // private static bool DetectCircleCircle(ICircleCollider2D left, ICircleCollider2D right, out CollisionDetectionInformation? collisionInformation)
    // {
    //     collisionInformation = default;

    //     Vector2D leftToRightCenter = left.CircleWorld.Center.FromTo(right.CircleWorld.Center);
    //     float distanceCircleCenter = leftToRightCenter.Magnitude;
    //     float radiusSum = left.CircleWorld.Radius + right.CircleWorld.Radius;

    //     float circleSurfaceDistance = distanceCircleCenter - radiusSum;

    //     bool collision = circleSurfaceDistance <= 0f;

    //     if (collision)
    //         collisionInformation = new(left, right, leftToRightCenter.Normalized, -circleSurfaceDistance);

    //     return collision;
    // }
}