From 64d440871478c1e943e41ee0f79d37daf0174b16 Mon Sep 17 00:00:00 2001
From: Joona Aalto <jondolf.dev@gmail.com>
Date: Sat, 13 Jul 2024 19:48:25 +0300
Subject: [PATCH] Fix contact constraints being cleared many times with many
 backends

---
 src/collision/narrow_phase.rs | 15 ++++++++++++---
 1 file changed, 12 insertions(+), 3 deletions(-)

diff --git a/src/collision/narrow_phase.rs b/src/collision/narrow_phase.rs
index 4d5200c0..f3117071 100644
--- a/src/collision/narrow_phase.rs
+++ b/src/collision/narrow_phase.rs
@@ -135,6 +135,18 @@ impl<C: AnyCollider> Plugin for NarrowPhasePlugin<C> {
         );
 
         if self.generate_constraints {
+            if is_first_instance {
+                // Clear contact constraints.
+                app.add_systems(
+                    self.schedule,
+                    (|mut constraints: ResMut<ContactConstraints>| {
+                        constraints.clear();
+                    })
+                    .after(NarrowPhaseSet::PostProcess)
+                    .before(NarrowPhaseSet::GenerateConstraints),
+                );
+            }
+
             // Generate contact constraints.
             app.add_systems(
                 self.schedule,
@@ -262,9 +274,6 @@ fn generate_constraints<C: AnyCollider>(
 ) {
     let delta_secs = time.delta_seconds_adjusted();
 
-    // Clear contact constraints.
-    constraints.clear();
-
     // TODO: Parallelize.
     for contacts in narrow_phase.collisions.get_internal().values() {
         let Ok([collider1, collider2]) = narrow_phase