Syntriax.Engine/Engine.Integration/Engine.Integration.MonoGame/Behaviours/MonoGameCamera3D.cs

using Microsoft.Xna.Framework;
using Microsoft.Xna.Framework.Graphics;

using Engine.Core;

namespace Engine.Integration.MonoGame;

public class MonoGameCamera3D : Behaviour, ICamera3D, IFirstFrameUpdate, IPreDraw
{
    public Event<MonoGameCamera3D, ViewChangedArguments> OnViewChanged { get; } = new();
    public Event<MonoGameCamera3D, ProjectionChangedArguments> OnProjectionChanged { get; } = new();
    public Event<MonoGameCamera3D, ViewportChangedArguments> OnViewportChanged { get; } = new();
    public Event<MonoGameCamera3D, FieldOfViewChangedArguments> OnFieldOfViewChanged { get; } = new();

    private Matrix _view = Matrix.Identity;
    private Matrix _projection = Matrix.Identity;
    private Viewport _viewport = default;
    private float _fieldOfView = 1f;

    public GraphicsDeviceManager Graphics { get; private set; } = null!;
    public ITransform3D Transform { get; private set; } = null!;

    public Matrix View
    {
        get => _view;
        set
        {
            if (_view == value)
                return;

            Matrix previousView = _view;
            _view = value;
            OnViewChanged.Invoke(this, new(previousView));
        }
    }
    public Matrix Projection
    {
        get => _projection;
        set
        {
            if (_projection == value)
                return;

            Matrix previousProjection = _projection;
            _projection = value;
            OnProjectionChanged.Invoke(this, new(previousProjection));
        }
    }

    public Vector3D Position
    {
        get => Transform.Position;
        set => Transform.Position = value;
    }

    public Viewport Viewport
    {
        get => _viewport;
        set
        {
            if (_viewport.Equals(value))
                return;

            Viewport previousViewport = _viewport;
            _viewport = value;
            OnViewportChanged.Invoke(this, new(previousViewport));
        }
    }

    public float FieldOfView
    {
        get => _fieldOfView;
        set
        {
            float newValue = Math.Max(0.1f, value);

            if (_fieldOfView == newValue)
                return;

            float previousFieldOfView = _fieldOfView;
            _fieldOfView = newValue;
            OnFieldOfViewChanged.Invoke(this, new(previousFieldOfView));
        }
    }

    public Engine.Core.Quaternion Rotation
    {
        get => Transform.Rotation;
        set => Transform.Rotation = value;
    }

    // TODO This causes delay since OnPreDraw calls assuming this is called in in Update 
    public Ray3D ScreenToWorldRay(Vector2D screenPosition)
    {
        Vector3 nearPoint = new(screenPosition.X, screenPosition.Y, 0f);
        Vector3 farPoint = new(screenPosition.X, screenPosition.Y, 1f);

        Vector3 worldNear = Viewport.Unproject(nearPoint, _projection, _view, Matrix.Identity);
        Vector3 worldFar = Viewport.Unproject(farPoint, _projection, _view, Matrix.Identity);

        Vector3 direction = Vector3.Normalize(worldFar - worldNear);
        return new(worldNear.ToVector3D(), direction.ToVector3D());
    }

    public Vector2D WorldToScreenPosition(Vector3D worldPosition) => Viewport.Project(worldPosition.ToVector3(), _projection, _view, Matrix.Identity).ToVector3D();

    public void FirstActiveFrame()
    {
        Graphics = BehaviourController.UniverseObject.Universe.FindRequiredBehaviour<MonoGameWindowContainer>().Window.Graphics;
        Viewport = Graphics.GraphicsDevice.Viewport;
    }

    public void PreDraw()
    {
        Vector3 cameraPosition = Position.ToVector3();
        View = Matrix.CreateLookAt(
            cameraPosition,
            Transform.Forward.ToVector3() + cameraPosition,
            Transform.Up.ToVector3()
        );
        Projection = Matrix.CreatePerspectiveFieldOfView(MathHelper.PiOver4, Viewport.AspectRatio, 0.1f, 100f);
    }

    protected sealed override void InitializeInternal() => Transform = BehaviourController.GetRequiredBehaviour<ITransform3D>();
    protected sealed override void FinalizeInternal() => Transform = null!;

    public readonly record struct ViewChangedArguments(Matrix PreviousView);
    public readonly record struct ProjectionChangedArguments(Matrix PreviousProjection);
    public readonly record struct ViewportChangedArguments(Viewport PreviousViewport);
    public readonly record struct FieldOfViewChangedArguments(float PreviousFieldOfView);
}