feat: Transform Hierarchy System

Engine.Core/Abstract/ITransform.cs

@@ -1,11 +1,12 @@
 using System;
+using System.Collections.Generic;
 
 namespace Syntriax.Engine.Core.Abstract;
 
 /// <summary>
 /// Represents the transformation properties of an object such as position, scale, and rotation.
 /// </summary>
-public interface ITransform
+public interface ITransform : IEnumerable<ITransform>
 {
     /// <summary>
     /// Event triggered when the <see cref="Position"/> of the <see cref="ITransform"/> changes.
@@ -23,17 +24,61 @@ public interface ITransform
     Action<ITransform>? OnRotationChanged { get; set; }
 
     /// <summary>
-    /// The position of the <see cref="ITransform"/> in 2D space.
+    /// Event triggered when the <see cref="Parent"/> of the <see cref="ITransform"/> changes. The second parameter is the old <see cref="ITransform"/>.
+    /// </summary>
+    Action<ITransform, ITransform?>? OnParentChanged { get; set; }
+
+    /// <summary>
+    /// Event triggered when a new <see cref="ITransform"/> is added to the <see cref="Children"/>.
+    /// </summary>
+    Action<ITransform, ITransform>? OnChildrenAdded { get; set; }
+
+    /// <summary>
+    /// Event triggered when an <see cref="ITransform"/> is removed from the <see cref="Children"/>.
+    /// </summary>
+    Action<ITransform, ITransform>? OnChildrenRemoved { get; set; }
+
+    /// <summary>
+    /// The world position of the <see cref="ITransform"/> in 2D space.
     /// </summary>
     Vector2D Position { get; set; }
 
     /// <summary>
-    /// The scale of the <see cref="ITransform"/>.
+    /// The world scale of the <see cref="ITransform"/>.
     /// </summary>
     Vector2D Scale { get; set; }
 
     /// <summary>
-    /// The rotation of the <see cref="ITransform"/> in degrees.
+    /// The world rotation of the <see cref="ITransform"/> in degrees.
     /// </summary>
     float Rotation { get; set; }
+
+    /// <summary>
+    /// The local position of the <see cref="ITransform"/> in 2D space.
+    /// </summary>
+    Vector2D LocalPosition { get; set; }
+
+    /// <summary>
+    /// The local scale of the <see cref="ITransform"/>.
+    /// </summary>
+    Vector2D LocalScale { get; set; }
+
+    /// <summary>
+    /// The local rotation of the <see cref="ITransform"/> in degrees.
+    /// </summary>
+    float LocalRotation { get; set; }
+
+    /// <summary>
+    /// The parent <see cref="ITransform"/> of the <see cref="ITransform"/>.
+    /// </summary>
+    ITransform? Parent { get; }
+
+    /// <summary>
+    /// The <see cref="ITransform"/>s that have this <see cref="ITransform"/> as their <see cref="Parent"/>.
+    /// </summary>
+    IReadOnlyList<ITransform> Children { get; }
+
+    void SetParent(ITransform? transform);
+    void AddChild(ITransform transform);
+    void RemoveChild(ITransform transform);
 }

Engine.Core/Extensions/TransformExtensions.cs

@@ -4,11 +4,16 @@ namespace Syntriax.Engine.Core;
 
 public static class TransformExtensions
 {
-    public static ITransform SetTransform(this ITransform transform, Vector2D? position = null, float? rotation = null, Vector2D? scale = null)
+    public static ITransform SetTransform(this ITransform transform,
+        Vector2D? position = null, float? rotation = null, Vector2D? scale = null,
+        Vector2D? localPosition = null, float? localRotation = null, Vector2D? localScale = null)
     {
         if (position.HasValue) transform.Position = position.Value;
         if (rotation.HasValue) transform.Rotation = rotation.Value;
         if (scale.HasValue) transform.Scale = scale.Value;
+        if (localPosition.HasValue) transform.LocalPosition = localPosition.Value;
+        if (localRotation.HasValue) transform.LocalRotation = localRotation.Value;
+        if (localScale.HasValue) transform.LocalScale = localScale.Value;
         return transform;
     }
 }

Engine.Core/Transform.cs

@@ -1,4 +1,6 @@
 using System;
+using System.Collections;
+using System.Collections.Generic;
 
 using Syntriax.Engine.Core.Abstract;
 
@@ -11,10 +13,25 @@ public class Transform : ITransform
     public Action<ITransform>? OnScaleChanged { get; set; } = null;
     public Action<ITransform>? OnRotationChanged { get; set; } = null;
 
+    public Action<ITransform, ITransform?>? OnParentChanged { get; set; } = null;
+    public Action<ITransform, ITransform>? OnChildrenAdded { get; set; } = null;
+    public Action<ITransform, ITransform>? OnChildrenRemoved { get; set; } = null;
+
+
     private Vector2D _position = Vector2D.Zero;
     private Vector2D _scale = Vector2D.One;
     private float _rotation = 0f;
 
+    private Vector2D _localPosition = Vector2D.Zero;
+    private Vector2D _localScale = Vector2D.One;
+    private float _localRotation = 0f;
+
+    private readonly List<ITransform> _children = [];
+
+    public ITransform? Parent { get; private set; } = null;
+
+    public IReadOnlyList<ITransform> Children => _children;
+
     public Vector2D Position
     {
         get => _position;
@@ -24,6 +41,7 @@ public class Transform : ITransform
                 return;
 
             _position = value;
+            UpdateLocalPosition();
             OnPositionChanged?.Invoke(this);
         }
     }
@@ -37,6 +55,7 @@ public class Transform : ITransform
                 return;
 
             _scale = value;
+            UpdateLocalScale();
             OnScaleChanged?.Invoke(this);
         }
     }
@@ -50,7 +69,180 @@ public class Transform : ITransform
                 return;
 
             _rotation = value;
+            UpdateLocalPosition();
             OnRotationChanged?.Invoke(this);
         }
     }
+
+    public Vector2D LocalPosition
+    {
+        get => _localPosition;
+        set
+        {
+            if (value == _localPosition)
+                return;
+
+            _localPosition = value;
+            UpdatePosition();
+            OnPositionChanged?.Invoke(this);
+        }
+    }
+
+    public Vector2D LocalScale
+    {
+        get => _localScale;
+        set
+        {
+            if (value == _localScale)
+                return;
+
+            _localScale = value;
+            UpdateScale();
+            OnScaleChanged?.Invoke(this);
+        }
+    }
+
+    public float LocalRotation
+    {
+        get => _localRotation;
+        set
+        {
+            if (value == _localRotation)
+                return;
+
+            _localRotation = value;
+            UpdateRotation();
+            OnRotationChanged?.Invoke(this);
+        }
+    }
+
+    public void SetParent(ITransform? transform)
+    {
+        if (transform == this || Parent == transform)
+            return;
+
+        ITransform? previousParent = Parent;
+        if (Parent is not null)
+        {
+            Parent.RemoveChild(this);
+            Parent.OnPositionChanged -= RecalculatePosition;
+            Parent.OnScaleChanged -= RecalculateScale;
+            Parent.OnRotationChanged -= RecalculateRotation;
+        }
+
+        Parent = transform;
+
+        if (transform is not null)
+        {
+            transform.AddChild(this);
+            transform.OnPositionChanged += RecalculatePosition;
+            transform.OnScaleChanged += RecalculateScale;
+            transform.OnRotationChanged += RecalculateRotation;
+        }
+
+        UpdateLocalPosition();
+        UpdateLocalScale();
+        UpdateLocalRotation();
+
+        OnParentChanged?.Invoke(this, previousParent);
+    }
+
+    public void AddChild(ITransform transform)
+    {
+        if (_children.Contains(transform))
+            return;
+
+        _children.Add(transform);
+        transform.SetParent(this);
+        OnChildrenAdded?.Invoke(this, transform);
+    }
+
+    public void RemoveChild(ITransform transform)
+    {
+        if (!_children.Remove(transform))
+            return;
+
+        transform.SetParent(null);
+        OnChildrenRemoved?.Invoke(this, transform);
+    }
+
+    public IEnumerator<ITransform> GetEnumerator() => _children.GetEnumerator();
+    IEnumerator IEnumerable.GetEnumerator() => _children.GetEnumerator();
+
+    private void RecalculatePosition(ITransform _)
+    {
+        if (Parent is null)
+            return;
+
+        UpdatePosition();
+        OnPositionChanged?.Invoke(this);
+    }
+
+    private void RecalculateScale(ITransform _)
+    {
+        if (Parent is null)
+            return;
+
+        UpdateScale();
+        OnScaleChanged?.Invoke(this);
+    }
+
+    private void RecalculateRotation(ITransform _)
+    {
+        if (Parent is null)
+            return;
+
+        UpdatePosition();
+        UpdateRotation();
+        OnPositionChanged?.Invoke(this);
+        OnRotationChanged?.Invoke(this);
+    }
+
+    private void UpdateLocalPosition()
+    {
+        if (Parent is null)
+            _localPosition = Position;
+        else
+            _localPosition = Parent.Position.FromTo(Position).Scale(Parent.Scale);
+    }
+
+    private void UpdateLocalScale()
+    {
+        if (Parent is null)
+            _localScale = Scale;
+        else
+            _localScale = Scale.Scale(new(1f / Parent.Scale.X, 1f / Parent.Scale.Y));
+    }
+
+    private void UpdateLocalRotation()
+    {
+        if (Parent is null)
+            _localRotation = Rotation;
+        else
+            _localRotation = Rotation - Parent.Rotation;
+    }
+
+    private void UpdatePosition()
+    {
+        if (Parent is null)
+            _position = LocalPosition.Scale(Vector2D.One).Rotate(0f * Math.DegreeToRadian);
+        else
+            _position = Parent.Position + LocalPosition.Scale(new(1f / Parent.Scale.X, 1f / Parent.Scale.Y)).Rotate(Parent.Rotation * Math.DegreeToRadian);
+    }
+
+    private void UpdateScale()
+    {
+        if (Parent is null)
+            _scale = LocalScale;
+        else
+            _scale = Vector2D.Scale(Parent.Scale, LocalScale);
+    }
+
+    private void UpdateRotation()
+    {
+        if (Parent is null)
+            _rotation = LocalRotation;
+        else
+            _rotation = Parent.Rotation + LocalRotation;
+    }
 }