⚡ Optimize AABB-Polygon intersection with early bounds rejection

src/GameUtils/Types/Geometry/AABB.cs

@@ -148,17 +148,43 @@ public bool Intersects(Line line, out Vector2[] intersectionPoints)
 #pragma warning disable S3267 // LINQ would reintroduce allocations on a hot collision path
     public bool Intersects(Polygon2D polygon)
     {
+        // 1. Fast bounds check: compute polygon bounds on the fly
+        if (polygon.Vertices.Length > 0)
+        {
+            var pMinX = polygon.Vertices[0].X;
+            var pMaxX = polygon.Vertices[0].X;
+            var pMinY = polygon.Vertices[0].Y;
+            var pMaxY = polygon.Vertices[0].Y;
+
+            for (int i = 1; i < polygon.Vertices.Length; i++)
+            {
+                var v = polygon.Vertices[i];
+                if (v.X < pMinX) pMinX = v.X;
+                if (v.X > pMaxX) pMaxX = v.X;
+                if (v.Y < pMinY) pMinY = v.Y;
+                if (v.Y > pMaxY) pMaxY = v.Y;
+            }
+
+            if (pMinX > Max.X || pMaxX < Min.X || pMinY > Max.Y || pMaxY < Min.Y)
+            {
+                return false;
+            }
+        }
+
+        // 2. Check if any polygon vertex is inside the AABB
         foreach (var v in polygon.Vertices)
         {
             if (Contains(v)) return true;
         }
 
+        // 3. Check if any polygon edge intersects the AABB
         foreach (var e in polygon.Edges)
         {
             if (Intersects(e)) return true;
         }
 
-        return false;
+        // 4. Check if the AABB is completely inside the polygon
+        return polygon.Contains(Center);
     }
 #pragma warning restore S3267
 

tests/GameUtils.Benchmarks/GameUtils.Benchmarks.csproj

@@ -0,0 +1,18 @@
+<Project Sdk="Microsoft.NET.Sdk">
+
+  <PropertyGroup>
+    <OutputType>Exe</OutputType>
+    <TargetFramework>net10.0</TargetFramework>
+    <ImplicitUsings>enable</ImplicitUsings>
+    <Nullable>enable</Nullable>
+  </PropertyGroup>
+
+  <ItemGroup>
+    <PackageReference Include="BenchmarkDotNet" Version="0.15.8" />
+  </ItemGroup>
+
+  <ItemGroup>
+    <ProjectReference Include="..\..\src\GameUtils\GameUtils.csproj" />
+  </ItemGroup>
+
+</Project>

tests/GameUtils.Benchmarks/Program.cs

@@ -0,0 +1,64 @@
+using BenchmarkDotNet.Running;
+using BenchmarkDotNet.Attributes;
+using GameUtils.Types.Geometry;
+using System.Numerics;
+using System.Linq;
+
+namespace GameUtils.Benchmarks
+{
+    [MemoryDiagnoser]
+    public class AABBIntersectsBenchmark
+    {
+        private AABB _aabb;
+        private Polygon2D _polyInside;
+        private Polygon2D _polyIntersecting;
+        private Polygon2D _polyOutside;
+        private Polygon2D _polyContainsAABB;
+
+        [GlobalSetup]
+        public void Setup()
+        {
+            _aabb = new AABB(new Vector2(10, 10), new Vector2(20, 20));
+
+            // Polygon completely inside AABB
+            _polyInside = new Polygon2D(new[] {
+                new Vector2(12, 12), new Vector2(18, 12), new Vector2(15, 18)
+            });
+
+            // Polygon intersecting AABB
+            _polyIntersecting = new Polygon2D(new[] {
+                new Vector2(5, 15), new Vector2(15, 15), new Vector2(10, 25)
+            });
+
+            // Polygon completely outside AABB
+            _polyOutside = new Polygon2D(new[] {
+                new Vector2(30, 30), new Vector2(40, 30), new Vector2(35, 40)
+            });
+
+            // Polygon containing the entire AABB
+            _polyContainsAABB = new Polygon2D(new[] {
+                new Vector2(0, 0), new Vector2(30, 0), new Vector2(30, 30), new Vector2(0, 30)
+            });
+        }
+
+        [Benchmark]
+        public bool IntersectsInside() => _aabb.Intersects(_polyInside);
+
+        [Benchmark]
+        public bool IntersectsIntersecting() => _aabb.Intersects(_polyIntersecting);
+
+        [Benchmark]
+        public bool IntersectsOutside() => _aabb.Intersects(_polyOutside);
+
+        [Benchmark]
+        public bool IntersectsContainsAABB() => _aabb.Intersects(_polyContainsAABB);
+    }
+
+    public class Program
+    {
+        public static void Main(string[] args)
+        {
+            var summary = BenchmarkRunner.Run<AABBIntersectsBenchmark>();
+        }
+    }
+}

tests/GameUtils.Tests/Geometry/AABBTests.cs

@@ -0,0 +1,53 @@
+using Microsoft.VisualStudio.TestTools.UnitTesting;
+using GameUtils.Types.Geometry;
+using System.Numerics;
+
+namespace GameUtils.Tests.Geometry;
+
+[TestClass]
+public class AABBTests
+{
+    [TestMethod]
+    public void Intersects_PolygonContainsAABB_ReturnsTrue()
+    {
+        var aabb = new AABB(new Vector2(10, 10), new Vector2(20, 20));
+        var polyContainsAABB = new Polygon2D(new[] {
+            new Vector2(0, 0), new Vector2(30, 0), new Vector2(30, 30), new Vector2(0, 30)
+        });
+
+        Assert.IsTrue(aabb.Intersects(polyContainsAABB));
+    }
+
+    [TestMethod]
+    public void Intersects_PolygonInsideAABB_ReturnsTrue()
+    {
+        var aabb = new AABB(new Vector2(10, 10), new Vector2(20, 20));
+        var polyInsideAABB = new Polygon2D(new[] {
+            new Vector2(12, 12), new Vector2(18, 12), new Vector2(15, 18)
+        });
+
+        Assert.IsTrue(aabb.Intersects(polyInsideAABB));
+    }
+
+    [TestMethod]
+    public void Intersects_PolygonIntersectingAABB_ReturnsTrue()
+    {
+        var aabb = new AABB(new Vector2(10, 10), new Vector2(20, 20));
+        var polyIntersectingAABB = new Polygon2D(new[] {
+            new Vector2(5, 15), new Vector2(15, 15), new Vector2(10, 25)
+        });
+
+        Assert.IsTrue(aabb.Intersects(polyIntersectingAABB));
+    }
+
+    [TestMethod]
+    public void Intersects_PolygonOutsideAABB_ReturnsFalse()
+    {
+        var aabb = new AABB(new Vector2(10, 10), new Vector2(20, 20));
+        var polyOutsideAABB = new Polygon2D(new[] {
+            new Vector2(30, 30), new Vector2(40, 30), new Vector2(35, 40)
+        });
+
+        Assert.IsFalse(aabb.Intersects(polyOutsideAABB));
+    }
+}