Add "Custom Filter" scene.

Author: MelvMay-Unity

LowLevel/Sandbox/Assets/Sandbox.unity

@@ -404,6 +404,10 @@ MonoBehaviour:
     Name: Conveyor Belt
     Category: Shapes
     Description: Demonstrates the use of the Tangent Speed surface material property.
+  - ScenePath: Assets/Scenes/Shapes/CustomFilter/CustomFilter.unity
+    Name: Custom Filter
+    Category: Shapes
+    Description: Demonstrates the use of a custom shape filter.
   - ScenePath: Assets/Scenes/Shapes/EllipsePolygons/EllipsePolygons.unity
     Name: Ellipse Polygons
     Category: Shapes

LowLevel/Sandbox/Assets/Scenes/Shapes/CustomFilter.meta

@@ -0,0 +1,144 @@
+using Unity.Collections;
+using UnityEngine;
+using UnityEngine.LowLevelPhysics2D;
+using UnityEngine.UIElements;
+
+public class CustomFilter : MonoBehaviour, PhysicsCallbacks.IContactFilterCallback
+{
+    private SandboxManager m_SandboxManager;
+    private SceneManifest m_SceneManifest;
+    private UIDocument m_UIDocument;
+    private CameraManipulator m_CameraManipulator;
+
+    private PhysicsWorld m_PhysicsWorld;
+    private bool m_OldContactFilterCallbacks;
+    
+    private Button m_SpawnButton;
+    private PhysicsBody m_ConveyorBeltBody;
+    private PhysicsShape m_ConveyorBeltShape;
+    
+    private void OnEnable()
+    {
+        m_SandboxManager = FindFirstObjectByType<SandboxManager>();
+        m_SceneManifest = FindFirstObjectByType<SceneManifest>();
+        m_UIDocument = GetComponent<UIDocument>();
+
+        m_CameraManipulator = FindFirstObjectByType<CameraManipulator>();
+        m_CameraManipulator.CameraSize = 12;
+        m_CameraManipulator.CameraPosition = new Vector2(0f, 7f);
+
+        // Set up the scene reset action.
+        m_SandboxManager.SceneResetAction = SetupScene;
+
+        // Set Overrides.
+        m_SandboxManager.SetOverrideColorShapeState(false);
+
+        m_PhysicsWorld = PhysicsWorld.defaultWorld;
+        
+        // Ensure the contact filter callbacks are on.
+        m_OldContactFilterCallbacks = m_PhysicsWorld.contactFilterCallbacks;
+        m_PhysicsWorld.contactFilterCallbacks = true;
+        
+        SetupOptions();
+
+        SetupScene();
+    }
+
+    private void OnDisable()
+    {
+        // Restore global default.
+        m_PhysicsWorld.contactFilterCallbacks = m_OldContactFilterCallbacks;
+        
+	    // Reset overrides.
+	    m_SandboxManager.ResetOverrideColorShapeState();        
+    }
+
+    private void SetupOptions()
+    {
+        var root = m_UIDocument.rootVisualElement;
+
+        {
+            // Menu Region (for camera manipulator).
+            var menuRegion = root.Q<VisualElement>("menu-region");
+            menuRegion.RegisterCallback<PointerEnterEvent>(_ => ++m_CameraManipulator.OverlapUI);
+            menuRegion.RegisterCallback<PointerLeaveEvent>(_ => --m_CameraManipulator.OverlapUI);
+            
+            // Reset Scene.
+            var resetScene = root.Q<Button>("reset-scene");
+            resetScene.clicked += SetupScene;
+
+            // Fetch the scene description.
+            var sceneDescription = root.Q<Label>("scene-description");
+            sceneDescription.text = $"\"{m_SceneManifest.LoadedSceneName}\"\n{m_SceneManifest.LoadedSceneDescription}";
+        }
+    }
+
+    private void SetupScene()
+    {
+        // Reset the scene state.
+        m_SandboxManager.ResetSceneState();
+
+        var bodies = m_SandboxManager.Bodies;
+
+        // Ground.
+        {
+            var body = m_PhysicsWorld.CreateBody();
+            bodies.Add(body);
+            using var vertices = new NativeList<Vector2>(Allocator.Temp)
+            {
+	            new(-20f, 0f),
+	            new(-20f, 10f),
+	            new(20f, 10f),
+	            new(20f, 0f)
+            };
+            body.CreateChain(new ChainGeometry(vertices.AsArray()), PhysicsChainDefinition.defaultDefinition);
+        }
+
+        // Create even/odd bodies.
+        {
+            var geometry = PolygonGeometry.CreateBox(Vector2.one * 2f, 0.2f);
+            var shapeDef = new PhysicsShapeDefinition { contactFilterCallbacks = true };
+            
+            for (var n = 0; n < 15; ++n)
+            {
+                var body = m_PhysicsWorld.CreateBody(new PhysicsBodyDefinition { bodyType = RigidbodyType2D.Dynamic, gravityScale = 4f, position = new Vector2(-17.5f + n * 2.5f, 4f) });
+
+                var colorGroup = n % 3;
+
+                // Set the color appropriately.
+                shapeDef.surfaceMaterial.customColor = colorGroup switch
+                {
+                    0 => Color.red,
+                    1 => Color.green,
+                    2 => Color.blue,
+                    _ => default
+                };
+
+                var shape = body.CreateShape(geometry, shapeDef);
+                
+                // Set the custom data.
+                shape.userData = new PhysicsUserData { intValue = colorGroup, boolValue = true };
+                
+                // Set the callback target.
+                shape.callbackTarget = this;
+            }
+        }
+    }
+
+    // Called when any shapes that are asking for a contact filter potentially come into contact.
+    // This must be thread-safe and should NOT perform any write operations to the physics engine!
+    public bool OnContactFilter2D(PhysicsEvents.ContactFilterEvent contactFilterEvent)
+    {
+        // Fetch the user-data from the shapes.
+        // NOTE: This is a (thread) safe way to pass custom-data.
+        var userData1 = contactFilterEvent.shapeA.userData;
+        var userData2 = contactFilterEvent.shapeB.userData;
+
+        // Allow contact if this isn't a filtered shape pair.
+        if (!userData1.boolValue || !userData2.boolValue)
+            return true;
+        
+        // Allow contact if in the same "color group".
+        return userData1.intValue == userData2.intValue;
+    }
+}