From 907972d245012518d7075afceaf499ad6c894011 Mon Sep 17 00:00:00 2001
From: Erik Onarheim <erik.onarheim@gmail.com>
Date: Fri, 31 Jan 2025 09:15:46 -0600
Subject: [PATCH] fix: composite multi contact (#3351)

This PR fixes and issue where composite colliders in the "together" strategy contacts were being resolved multiple times in the ArcadeSolver causing visual jitter/artifacts
---
 src/engine/Collision/Colliders/Shape.ts        |  2 ++
 src/engine/Collision/CollisionSystem.ts        |  2 +-
 .../Collision/Detection/CollisionContact.ts    |  2 +-
 src/engine/Collision/Solver/ArcadeSolver.ts    | 18 +++++++++++++++++-
 4 files changed, 21 insertions(+), 3 deletions(-)

diff --git a/src/engine/Collision/Colliders/Shape.ts b/src/engine/Collision/Colliders/Shape.ts
index da92ad2ee..f0fda3702 100644
--- a/src/engine/Collision/Colliders/Shape.ts
+++ b/src/engine/Collision/Colliders/Shape.ts
@@ -91,6 +91,7 @@ export class Shape {
         Shape.Box(width, height - width, Vector.Half, offset),
         Shape.Circle(width / 2, vec(0, height / 2 - width / 2).add(offset))
       ]);
+      capsule.compositeStrategy = 'together';
       return capsule;
     } else {
       // width > height, if equal maybe use a circle
@@ -99,6 +100,7 @@ export class Shape {
         Shape.Box(width - height, height, Vector.Half, offset),
         Shape.Circle(height / 2, vec(width / 2 - height / 2, 0).add(offset))
       ]);
+      capsule.compositeStrategy = 'together';
       return capsule;
     }
   }
diff --git a/src/engine/Collision/CollisionSystem.ts b/src/engine/Collision/CollisionSystem.ts
index 7d27c3d67..1356401ec 100644
--- a/src/engine/Collision/CollisionSystem.ts
+++ b/src/engine/Collision/CollisionSystem.ts
@@ -113,7 +113,7 @@ export class CollisionSystem extends System {
     this._currentFrameContacts.clear();
 
     // Given possible pairs find actual contacts
-    let contacts: CollisionContact[] = []; // = this._processor.narrowphase(pairs, this._engine?.debug?.stats?.currFrame);
+    let contacts: CollisionContact[] = [];
 
     const solver: CollisionSolver = this.getSolver();
 
diff --git a/src/engine/Collision/Detection/CollisionContact.ts b/src/engine/Collision/Detection/CollisionContact.ts
index a1c724c3e..8f50698a5 100644
--- a/src/engine/Collision/Detection/CollisionContact.ts
+++ b/src/engine/Collision/Detection/CollisionContact.ts
@@ -80,7 +80,7 @@ export class CollisionContact {
     this.info = info;
     this.id = Pair.calculatePairHash(colliderA.id, colliderB.id);
     if (colliderA.composite || colliderB.composite) {
-      // Add on the parent composite pair for start/end contact if 'together
+      // Add on the parent composite pair for start/end contact if 'together'
       const colliderAId = colliderA.composite?.compositeStrategy === 'separate' ? colliderA.id : colliderA.composite?.id ?? colliderA.id;
       const colliderBId = colliderB.composite?.compositeStrategy === 'separate' ? colliderB.id : colliderB.composite?.id ?? colliderB.id;
       this.id += '|' + Pair.calculatePairHash(colliderAId, colliderBId);
diff --git a/src/engine/Collision/Solver/ArcadeSolver.ts b/src/engine/Collision/Solver/ArcadeSolver.ts
index 7c27251f2..523bfe899 100644
--- a/src/engine/Collision/Solver/ArcadeSolver.ts
+++ b/src/engine/Collision/Solver/ArcadeSolver.ts
@@ -69,15 +69,30 @@ export class ArcadeSolver implements CollisionSolver {
     return contacts;
   }
 
+  private _compositeContactsIds = new Set<string>();
   public preSolve(contacts: CollisionContact[]) {
     const epsilon = 0.0001;
     for (let i = 0; i < contacts.length; i++) {
       const contact = contacts[i];
+
+      // Cancel dup composite together strategy contacts
+      const index = contact.id.indexOf('|');
+      if (index > 0) {
+        const compositeId = contact.id.substring(index + 1);
+        if (this._compositeContactsIds.has(compositeId)) {
+          contact.cancel();
+          continue;
+        }
+        this._compositeContactsIds.add(compositeId);
+      }
+
+      // Cancel near 0 mtv collisions
       if (Math.abs(contact.mtv.x) < epsilon && Math.abs(contact.mtv.y) < epsilon) {
-        // Cancel near 0 mtv collisions
         contact.cancel();
         continue;
       }
+
+      // Record distance/direction for sorting
       const side = Side.fromDirection(contact.mtv);
       const mtv = contact.mtv.negate();
 
@@ -93,6 +108,7 @@ export class ArcadeSolver implements CollisionSolver {
         new PreCollisionEvent(contact.colliderB, contact.colliderA, Side.getOpposite(side), mtv.negate(), contact)
       );
     }
+    this._compositeContactsIds.clear();
   }
 
   public postSolve(contacts: CollisionContact[]) {