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, ILastFrameUpdate, IPreDraw
{
    public Event<MonoGameCamera3D, ViewChangedArguments> OnViewChanged { get; } = new();
    public Event<MonoGameCamera3D, ProjectionChangedArguments> OnProjectionChanged { get; } = new();
    public Event<MonoGameCamera3D, ViewportChangedArguments> OnViewportChanged { get; } = new();

    public Event<ICamera3D, ICamera3D.NearPlaneChangedArguments> OnNearPlaneChanged { get; } = new();
    public Event<ICamera3D, ICamera3D.FarPlaneChangedArguments> OnFarPlaneChanged { get; } = new();
    public Event<ICamera3D, ICamera3D.FieldOfViewChangedArguments> OnFieldOfViewChanged { get; } = new();

    private Matrix _view = Matrix.Identity;
    private Matrix _projection = Matrix.Identity;
    private Viewport _viewport = default;
    private float _nearPlane = 0.01f;
    private float _farPlane = 100f;
    private float _fieldOfView = Math.DegreeToRadian * 70f;
    private bool isRecalculationNeeded = true;

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

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

    public float NearPlane
    {
        get => _nearPlane;
        set
        {
            float previousNearPlane = _nearPlane;
            _nearPlane = value.Max(0.0001f);
            SetForRecalculation();
            OnNearPlaneChanged.Invoke(this, new(previousNearPlane));
        }
    }

    public float FarPlane
    {
        get => _farPlane;
        set
        {
            float previousFarPlane = _farPlane;
            _farPlane = value.Max(NearPlane);
            SetForRecalculation();
            OnFarPlaneChanged.Invoke(this, new(previousFarPlane));
        }
    }

    public float FieldOfView
    {
        get => _fieldOfView * Math.RadianToDegree;
        set
        {
            value = value.Max(0.1f) * Math.DegreeToRadian;

            if (_fieldOfView == value)
                return;

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

    // 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 LastActiveFrame() => Transform.OnTransformUpdated.RemoveListener(SetDirtyOnTransformUpdate);
    public void FirstActiveFrame()
    {
        Transform = BehaviourController.GetRequiredBehaviour<ITransform3D>();
        Graphics = BehaviourController.UniverseObject.Universe.FindRequiredBehaviour<MonoGameWindowContainer>().Window.Graphics;
        Viewport = Graphics.GraphicsDevice.Viewport;

        Transform.OnTransformUpdated.AddListener(SetDirtyOnTransformUpdate);
    }

    private void SetDirtyOnTransformUpdate(ITransform3D sender) => SetForRecalculation();
    private void SetForRecalculation() => isRecalculationNeeded = true;

    public void PreDraw()
    {
        if (!isRecalculationNeeded)
            return;

        CalculateView();
        CalculateProjection();
        isRecalculationNeeded = false;
    }

    private void CalculateView()
    {
        Vector3 forward = Vector3.Normalize(Transform.Forward.ToVector3());
        Vector3 up = Vector3.Normalize(Transform.Up.ToVector3());
        Vector3 right = Vector3.Normalize(Transform.Right.ToVector3());
        Vector3 position = Transform.Position.ToVector3();

        View = new Matrix(
            right.X, up.X, forward.X, 0,
            right.Y, up.Y, forward.Y, 0,
            right.Z, up.Z, forward.Z, 0,
            -Vector3.Dot(right, position),
            -Vector3.Dot(up, position),
            -Vector3.Dot(forward, position),
            1
        );
    }

    private void CalculateProjection()
    {
        float yScale = 1f / (float)Math.Tan(_fieldOfView / 2f);
        float xScale = yScale / Viewport.AspectRatio;

        Projection = new Matrix(
            xScale, 0, 0, 0,
            0, yScale, 0, 0,
            0, 0, _farPlane / (_farPlane - _nearPlane), 1,
            0, 0, -_nearPlane * _farPlane / (_farPlane - _nearPlane), 0
        );
    }

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