From c0847e19554ebd3d931a7bad226ff12cce8b6869 Mon Sep 17 00:00:00 2001
From: Max Cahill <1bardesign@gmail.com>
Date: Thu, 20 Jan 2022 17:37:40 +1100
Subject: [PATCH] fixed intersect.bounce_off bouncing if the velocity was
 already going away from the normal

---
 intersect.lua | 13 ++++++++-----
 1 file changed, 8 insertions(+), 5 deletions(-)

diff --git a/intersect.lua b/intersect.lua
index f4ddf16..a6f3ca5 100644
--- a/intersect.lua
+++ b/intersect.lua
@@ -508,11 +508,14 @@ function intersect.bounce_off(velocity, normal, conservation)
 	conservation = conservation or 1
 	--take a copy, we need it
 	local old_vel = velocity:pooled_copy()
-	--reject on the normal (keep velocity tangential to the normal)
-	velocity:vector_rejection_inplace(normal)
-	--add back the complement of the difference;
-	--basically "flip" the velocity in line with the normal.
-	velocity:fused_multiply_add_inplace(old_vel:vector_sub_inplace(velocity), -conservation)
+	--heading into the normal
+	if old_vel:dot(normal) < 0 then
+		--reject on the normal (keep velocity tangential to the normal)
+		velocity:vector_rejection_inplace(normal)
+		--add back the complement of the difference;
+		--basically "flip" the velocity in line with the normal.
+		velocity:fused_multiply_add_inplace(old_vel:vector_sub_inplace(velocity), -conservation)
+	end
 	--clean up
 	old_vel:release()
 	return velocity