From 61ff0887e2770465bb8623e4641f05471cd9a8a1 Mon Sep 17 00:00:00 2001
From: Syntriax <syntriax@gmail.com>
Date: Sun, 19 Oct 2025 00:28:40 +0300
Subject: [PATCH] feat: 3D camera added

---
 Engine.Core/Abstract/ICamera3D.cs             |  26 ++++
 .../Behaviours/MonoGameCamera3D.cs            | 131 ++++++++++++++++++
 2 files changed, 157 insertions(+)
 create mode 100644 Engine.Core/Abstract/ICamera3D.cs
 create mode 100644 Engine.Integration/Engine.Integration.MonoGame/Behaviours/MonoGameCamera3D.cs

diff --git a/Engine.Core/Abstract/ICamera3D.cs b/Engine.Core/Abstract/ICamera3D.cs
new file mode 100644
index 0000000..01ce185
--- /dev/null
+++ b/Engine.Core/Abstract/ICamera3D.cs
@@ -0,0 +1,26 @@
+namespace Engine.Core;
+
+/// <summary>
+/// Represents a 3D camera in the engine.
+/// </summary>
+public interface ICamera3D : IBehaviour3D
+{
+    /// <summary>
+    /// Field of View (FOV) value of the camera
+    /// </summary>
+    float FieldOfView { get; set; }
+
+    /// <summary>
+    /// Converts a position from screen coordinates to a <see cref="Ray3D"/>.
+    /// </summary>
+    /// <param name="screenPosition">The position in screen coordinates.</param>
+    /// <returns>The <see cref="Ray3D"/> originating from the camera to the screen position in world coordinates.</returns>
+    Ray3D ScreenToWorldRay(Vector2D screenPosition);
+
+    /// <summary>
+    /// Converts a position from world coordinates to screen coordinates.
+    /// </summary>
+    /// <param name="worldPosition">The position in world coordinates.</param>
+    /// <returns>The position in screen coordinates.</returns>
+    Vector2D WorldToScreenPosition(Vector3D worldPosition);
+}
diff --git a/Engine.Integration/Engine.Integration.MonoGame/Behaviours/MonoGameCamera3D.cs b/Engine.Integration/Engine.Integration.MonoGame/Behaviours/MonoGameCamera3D.cs
new file mode 100644
index 0000000..6a9440f
--- /dev/null
+++ b/Engine.Integration/Engine.Integration.MonoGame/Behaviours/MonoGameCamera3D.cs
@@ -0,0 +1,131 @@
+using Microsoft.Xna.Framework;
+using Microsoft.Xna.Framework.Graphics;
+
+using Engine.Core;
+
+namespace Engine.Integration.MonoGame;
+
+public class MonoGameCamera3D : BehaviourBase, 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);
+}