From 8cf7aee0092d576c4520c6f5e6c6e7c5e5606edf Mon Sep 17 00:00:00 2001
From: Andrew Meadows <andrew@highfidelity.io>
Date: Fri, 30 Dec 2016 14:13:11 -0800
Subject: [PATCH] fix bug: second collision event with bad data

---
 libraries/entities-renderer/src/EntityTreeRenderer.cpp | 5 ++++-
 libraries/shared/src/RegisteredMetaTypes.cpp           | 6 ++++++
 libraries/shared/src/RegisteredMetaTypes.h             | 6 ++++--
 3 files changed, 14 insertions(+), 3 deletions(-)

diff --git a/libraries/entities-renderer/src/EntityTreeRenderer.cpp b/libraries/entities-renderer/src/EntityTreeRenderer.cpp
index 0e7fbee5c1..da06a07552 100644
--- a/libraries/entities-renderer/src/EntityTreeRenderer.cpp
+++ b/libraries/entities-renderer/src/EntityTreeRenderer.cpp
@@ -1060,7 +1060,10 @@ void EntityTreeRenderer::entityCollisionWithEntity(const EntityItemID& idA, cons
         playEntityCollisionSound(entityB, collision);
         emit collisionWithEntity(idB, idA, collision);
         if (_entitiesScriptEngine) {
-            _entitiesScriptEngine->callEntityScriptMethod(idB, "collisionWithEntity", idA, collision);
+            // since we're swapping A and B we need to send the inverted collision
+            Collision invertedCollision(collision);
+            invertedCollision.invert();
+            _entitiesScriptEngine->callEntityScriptMethod(idB, "collisionWithEntity", idA, invertedCollision);
         }
     }
 }
diff --git a/libraries/shared/src/RegisteredMetaTypes.cpp b/libraries/shared/src/RegisteredMetaTypes.cpp
index 984529c4ba..7f12d6cc00 100644
--- a/libraries/shared/src/RegisteredMetaTypes.cpp
+++ b/libraries/shared/src/RegisteredMetaTypes.cpp
@@ -742,6 +742,12 @@ void collisionFromScriptValue(const QScriptValue &object, Collision& collision)
     // TODO: implement this when we know what it means to accept collision events from JS
 }
 
+void Collision::invert() {
+    std::swap(idA, idB);
+    contactPoint += penetration;
+    penetration *= -1.0f;
+}
+
 QScriptValue quuidToScriptValue(QScriptEngine* engine, const QUuid& uuid) {
     if (uuid.isNull()) {
         return QScriptValue::NullValue;
diff --git a/libraries/shared/src/RegisteredMetaTypes.h b/libraries/shared/src/RegisteredMetaTypes.h
index 2aefd3aa47..498a8b3b3a 100644
--- a/libraries/shared/src/RegisteredMetaTypes.h
+++ b/libraries/shared/src/RegisteredMetaTypes.h
@@ -142,11 +142,13 @@ public:
               const glm::vec3& cPenetration, const glm::vec3& velocityChange)
     :   type(cType), idA(cIdA), idB(cIdB), contactPoint(cPoint), penetration(cPenetration), velocityChange(velocityChange) { }
 
+    void invert(); // swap A and B
+
     ContactEventType type;
     QUuid idA;
     QUuid idB;
-    glm::vec3 contactPoint;
-    glm::vec3 penetration;
+    glm::vec3 contactPoint; // on B in world-frame
+    glm::vec3 penetration; // from B towards A in world-frame
     glm::vec3 velocityChange;
 };
 Q_DECLARE_METATYPE(Collision)