feat: added raycasting support for physics engine 2D

Engine.Physics2D/Abstract/IPhysicsEngine2D.cs

@@ -1,3 +1,5 @@
+using System.Collections.Generic;
+
 using Syntriax.Engine.Core;
 
 namespace Syntriax.Engine.Physics2D;
@@ -35,6 +37,26 @@ public interface IPhysicsEngine2D
     /// <param name="deltaTime">The time step.</param>
     void StepIndividual(IRigidBody2D rigidBody, float deltaTime);
 
+    /// <summary>
+    /// Casts a <see cref="Ray2D"/> into the scene and returns the closest <see cref="RaycastResult"/> it hits, if any.
+    /// </summary>
+    /// <param name="ray">The <see cref="Ray2D"/> to cast.</param>
+    /// <param name="length">The maximum distance to check for intersections. Defaults to <see cref="float.MaxValue"/>.</param>
+    /// <returns>
+    /// A <see cref="RaycastResult"/> containing information about the hit, or <see cref="null"/> if no hit was detected.
+    /// </returns>
+    RaycastResult? Raycast(Ray2D ray, float length = float.MaxValue);
+
+    /// <summary>
+    /// Casts a <see cref="Ray2D"/> into the scene and stores all hit results in the provided list.
+    /// </summary>
+    /// <param name="ray">The <see cref="Ray2D"/> to cast.</param>
+    /// <param name="results">
+    /// A list to which all <see cref="RaycastResult"/>s will be added. The list will be populated with zero or more <see cref="RaycastResult"/> objects.
+    /// </param>
+    /// <param name="length">The maximum distance to check for intersections. Defaults to <see cref="float.MaxValue"/>.</param>
+    void Raycast(Ray2D ray, IList<RaycastResult> results, float length = float.MaxValue);
+
     readonly record struct PhysicsIterationArguments(IPhysicsEngine2D Sender, float IterationDeltaTime);
     readonly record struct PhysicsStepArguments(IPhysicsEngine2D Sender, float StepDeltaTime);
 }

Engine.Physics2D/Abstract/IRaycastResolver2D.cs

@@ -0,0 +1,23 @@
+using Syntriax.Engine.Core;
+
+namespace Syntriax.Engine.Physics2D;
+
+/// <summary>
+/// Represents a 2D raycast resolver.
+/// </summary>
+public interface IRaycastResolver2D
+{
+    /// <summary>
+    /// Casts a <see cref="Ray2D"/> against a specific <see cref="ICollider2D"/> shape and returns the first hit, if any.
+    /// </summary>
+    /// <typeparam name="T">The type of the <see cref="ICollider2D"/>, which must implement <see cref="ICollider2D"/>.</typeparam>
+    /// <param name="shape">The <see cref="ICollider2D"/> shape to test against.</param>
+    /// <param name="ray">The <see cref="Ray2D"/> to cast.</param>
+    /// <param name="length">
+    /// The maximum distance to check along the <see cref="Ray2D"/>. Defaults to <see cref="float.MaxValue"/>.
+    /// </param>
+    /// <returns>
+    /// A <see cref="RaycastResult"/> containing information about the intersection, or <see cref="null"/> if there was no hit.
+    /// </returns>
+    RaycastResult? RaycastAgainst<T>(T shape, Ray2D ray, float length = float.MaxValue) where T : ICollider2D;
+}

Engine.Physics2D/Abstract/RaycastResult.cs

@@ -0,0 +1,14 @@
+using Syntriax.Engine.Core;
+
+namespace Syntriax.Engine.Physics2D;
+
+public readonly struct RaycastResult(Ray2D ray, ICollider2D collider2D, Vector2D position, Vector2D normal)
+{
+    public readonly Ray2D Ray = ray;
+
+    public readonly Vector2D Position = position;
+    public readonly Vector2D Normal = normal;
+
+    public readonly ICollider2D Collider2D = collider2D;
+    public readonly RigidBody2D? RigidBody2D = collider2D.BehaviourController.GetBehaviourInParent<RigidBody2D>();
+}

Engine.Physics2D/PhysicsEngine2D.cs

@@ -15,6 +15,7 @@ public class PhysicsEngine2D : Behaviour, IPreUpdate, IPhysicsEngine2D
 
     protected readonly ICollisionDetector2D collisionDetector = null!;
     protected readonly ICollisionResolver2D collisionResolver = null!;
+    protected readonly IRaycastResolver2D raycastResolver = null!;
 
     private static Comparer<IBehaviour> SortByPriority() => Comparer<IBehaviour>.Create((x, y) => y.Priority.CompareTo(x.Priority));
     protected ActiveBehaviourCollectorSorted<IPrePhysicsUpdate> physicsPreUpdateCollector = new() { SortBy = SortByPriority() };
@@ -27,6 +28,35 @@ public class PhysicsEngine2D : Behaviour, IPreUpdate, IPhysicsEngine2D
     public int IterationPerStep { get => _iterationPerStep; set => _iterationPerStep = value < 1 ? 1 : value; }
     public float IterationPeriod { get => _iterationPeriod; set => _iterationPeriod = value.Max(0.0001f); }
 
+    public RaycastResult? Raycast(Ray2D ray, float length = float.MaxValue)
+    {
+        RaycastResult? closestResult = null;
+        float closestDistance = float.MaxValue;
+
+        for (int i = 0; i < colliderCollector.Count; i++)
+            if (raycastResolver.RaycastAgainst(colliderCollector[i], ray, length) is RaycastResult raycastResult)
+            {
+                float magnitudeSquared = raycastResult.Position.FromTo(ray.Origin).MagnitudeSquared;
+
+                if (magnitudeSquared > closestDistance)
+                    continue;
+
+                closestDistance = magnitudeSquared;
+                closestResult = raycastResult;
+            }
+
+        return closestResult;
+    }
+
+    public void Raycast(Ray2D ray, IList<RaycastResult> results, float length = float.MaxValue)
+    {
+        results.Clear();
+
+        for (int i = 0; i < colliderCollector.Count; i++)
+            if (raycastResolver.RaycastAgainst(colliderCollector[i], ray, length) is RaycastResult raycastResult)
+                results.Add(raycastResult);
+    }
+
     public void Step(float deltaTime)
     {
         float intervalDeltaTime = deltaTime / IterationPerStep;
@@ -216,13 +246,15 @@ public class PhysicsEngine2D : Behaviour, IPreUpdate, IPhysicsEngine2D
     {
         collisionDetector = new CollisionDetector2D();
         collisionResolver = new CollisionResolver2D();
+        raycastResolver = new RaycastResolver2D();
         Priority = int.MaxValue;
     }
 
-    public PhysicsEngine2D(ICollisionDetector2D collisionDetector, ICollisionResolver2D collisionResolver)
+    public PhysicsEngine2D(ICollisionDetector2D collisionDetector, ICollisionResolver2D collisionResolver, IRaycastResolver2D raycastResolver)
     {
         this.collisionDetector = collisionDetector;
         this.collisionResolver = collisionResolver;
+        this.raycastResolver = raycastResolver;
         Priority = int.MaxValue;
     }
 }

Engine.Physics2D/PhysicsEngine2DStandalone.cs

@@ -19,6 +19,7 @@ public class PhysicsEngine2DStandalone : IPhysicsEngine2D
 
     private readonly ICollisionDetector2D collisionDetector = null!;
     private readonly ICollisionResolver2D collisionResolver = null!;
+    private readonly IRaycastResolver2D raycastResolver = null!;
 
     public int IterationPerStep { get => _iterationCount; set => _iterationCount = value < 1 ? 1 : value; }
 
@@ -43,6 +44,34 @@ public class PhysicsEngine2DStandalone : IPhysicsEngine2D
         rigidBody.BehaviourController.OnBehaviourAdded.RemoveListener(delegateOnBehaviourAdded);
         rigidBody.BehaviourController.OnBehaviourRemoved.RemoveListener(delegateOnBehaviourRemoved);
     }
+    public RaycastResult? Raycast(Ray2D ray, float length = float.MaxValue)
+    {
+        RaycastResult? closestResult = null;
+        float closestDistance = float.MaxValue;
+
+        for (int i = 0; i < colliders.Count; i++)
+            if (raycastResolver.RaycastAgainst(colliders[i], ray, length) is RaycastResult raycastResult)
+            {
+                float magnitudeSquared = raycastResult.Position.FromTo(ray.Origin).MagnitudeSquared;
+
+                if (magnitudeSquared > closestDistance)
+                    continue;
+
+                closestDistance = magnitudeSquared;
+                closestResult = raycastResult;
+            }
+
+        return closestResult;
+    }
+
+    public void Raycast(Ray2D ray, IList<RaycastResult> results, float length = float.MaxValue)
+    {
+        results.Clear();
+
+        for (int i = 0; i < colliders.Count; i++)
+            if (raycastResolver.RaycastAgainst(colliders[i], ray, length) is RaycastResult raycastResult)
+                results.Add(raycastResult);
+    }
 
     public void Step(float deltaTime)
     {
@@ -203,15 +232,17 @@ public class PhysicsEngine2DStandalone : IPhysicsEngine2D
     {
         collisionDetector = new CollisionDetector2D();
         collisionResolver = new CollisionResolver2D();
+        raycastResolver = new RaycastResolver2D();
 
         delegateOnBehaviourAdded = OnBehaviourAdded;
         delegateOnBehaviourRemoved = OnBehaviourRemoved;
     }
 
-    public PhysicsEngine2DStandalone(ICollisionDetector2D collisionDetector, ICollisionResolver2D collisionResolver)
+    public PhysicsEngine2DStandalone(ICollisionDetector2D collisionDetector, ICollisionResolver2D collisionResolver, IRaycastResolver2D raycastResolver)
     {
         this.collisionDetector = collisionDetector;
         this.collisionResolver = collisionResolver;
+        this.raycastResolver = raycastResolver;
 
         delegateOnBehaviourAdded = OnBehaviourAdded;
         delegateOnBehaviourRemoved = OnBehaviourRemoved;

Engine.Physics2D/RaycastResolver2D.cs

@@ -0,0 +1,102 @@
+using System.Collections.Generic;
+
+using Syntriax.Engine.Core;
+
+namespace Syntriax.Engine.Physics2D;
+
+public class RaycastResolver2D : IRaycastResolver2D
+{
+    private readonly Pool<List<Line2D>> lineCacheQueue = new(() => new List<Line2D>(4));
+
+    RaycastResult? IRaycastResolver2D.RaycastAgainst<T>(T shape, Ray2D ray, float length)
+    {
+        if (shape is IShapeCollider2D shapeCollider)
+            return RaycastAgainstShape(shapeCollider, ray, length);
+        else if (shape is ICircleCollider2D circleCollider)
+            return RaycastAgainstCircle(circleCollider, ray, length);
+
+        throw new System.NotSupportedException($"{shape.GetType().FullName} is not supported by {GetType().FullName}. Please implement a {nameof(IRaycastResolver2D)} and use it as the raycast resolver.");
+    }
+
+    public RaycastResult? RaycastAgainstShape(IShapeCollider2D shapeCollider, Ray2D ray, float length)
+    {
+        List<Line2D> line2Ds = lineCacheQueue.Get();
+        line2Ds.Clear();
+
+        RaycastResult? raycastResult = null;
+        float closestRaycastResultSquared = float.MaxValue;
+
+        shapeCollider.ShapeWorld.ToLines(line2Ds);
+
+        Line2D rayLine = ray.ToLine(length);
+
+        foreach (Line2D line in line2Ds)
+        {
+            if (line.Intersects(rayLine))
+            {
+                Vector2D hitPosition = line.IntersectionPoint(rayLine);
+
+                float hitDistanceSquared = ray.Origin.FromTo(hitPosition).MagnitudeSquared;
+
+                if (closestRaycastResultSquared < hitDistanceSquared)
+                    continue;
+
+                closestRaycastResultSquared = hitDistanceSquared;
+
+                Vector2D lineDirection = line.Direction;
+
+                Vector2D normal1 = lineDirection.Perpendicular();
+                Vector2D normal2 = -lineDirection.Perpendicular();
+
+                float normalDot1 = rayLine.Direction.Dot(normal1);
+                float normalDot2 = rayLine.Direction.Dot(normal2);
+
+                Vector2D hitNormal = normalDot1 < normalDot2 ? normal1 : normal2;
+
+                if (shapeCollider.ShapeWorld.Overlaps(ray.Origin))
+                    hitNormal = hitNormal.Reversed;
+
+                raycastResult = new(ray, shapeCollider, hitPosition, hitNormal);
+            }
+        }
+
+        line2Ds.Clear();
+        lineCacheQueue.Return(line2Ds);
+
+        return raycastResult;
+    }
+
+    public RaycastResult? RaycastAgainstCircle(ICircleCollider2D circleCollider, Ray2D ray, float length)
+    {
+        Circle circle = circleCollider.CircleWorld;
+
+        if (circle.Overlaps(ray.Origin, out _, out float depth))
+        {
+            Vector2D insideNormal = circle.Center.FromTo(ray.Origin).Normalized;
+            Vector2D insidePosition = circle.Center + insideNormal * circle.Radius;
+
+            return new(ray, circleCollider, insidePosition, insideNormal);
+        }
+
+        Vector2D originToCircle = ray.Origin.FromTo(circle.Center);
+        float distanceToClosest = ray.Direction.Dot(originToCircle);
+
+        Vector2D closestPoint = ray.Origin + ray.Direction * distanceToClosest;
+        Vector2D closestPointToCircle = closestPoint.FromTo(circle.Center);
+
+        float closestToCircleDistanceSquared = closestPointToCircle.MagnitudeSquared;
+
+        if (closestToCircleDistanceSquared > circle.RadiusSquared)
+            return null;
+
+        float distanceToHit = distanceToClosest - (circle.Radius - closestToCircleDistanceSquared.Sqrt());
+
+        if (distanceToHit > length || distanceToHit < 0f)
+            return null;
+
+        Vector2D hitPosition = ray.Evaluate(distanceToHit);
+        Vector2D hitNormal = circle.Center.FromTo(hitPosition).Normalized;
+
+        return new(ray, circleCollider, hitPosition, hitNormal);
+    }
+}