From 22fd4a7116cbfa641341004db81983453e379166 Mon Sep 17 00:00:00 2001
From: Seth Alves <seth.alves@gmail.com>
Date: Sat, 14 Apr 2018 12:27:58 -0700
Subject: [PATCH] fix bug that caused tractor action to go crazy if only one of
 the two entities it connected were known to interface

---
 libraries/physics/src/ObjectActionTractor.cpp | 13 +++++++++----
 1 file changed, 9 insertions(+), 4 deletions(-)

diff --git a/libraries/physics/src/ObjectActionTractor.cpp b/libraries/physics/src/ObjectActionTractor.cpp
index bc68d6de73..9b2da22665 100644
--- a/libraries/physics/src/ObjectActionTractor.cpp
+++ b/libraries/physics/src/ObjectActionTractor.cpp
@@ -47,19 +47,22 @@ ObjectActionTractor::~ObjectActionTractor() {
 bool ObjectActionTractor::getTarget(float deltaTimeStep, glm::quat& rotation, glm::vec3& position,
                                    glm::vec3& linearVelocity, glm::vec3& angularVelocity,
                                    float& linearTimeScale, float& angularTimeScale) {
-    SpatiallyNestablePointer other = getOther();
+    bool success { true };
+    EntityItemPointer other = std::dynamic_pointer_cast<EntityItem>(getOther());
     withReadLock([&]{
         linearTimeScale = _linearTimeScale;
         angularTimeScale = _angularTimeScale;
 
         if (!_otherID.isNull()) {
-            if (other) {
+            if (other && other->isReadyToComputeShape()) {
                 rotation = _desiredRotationalTarget * other->getWorldOrientation();
                 position = other->getWorldOrientation() * _desiredPositionalTarget + other->getWorldPosition();
             } else {
-                // we should have an "other" but can't find it, so disable the tractor.
+                // we should have an "other" but can't find it, or its collision shape isn't loaded,
+                // so disable the tractor.
                 linearTimeScale = FLT_MAX;
                 angularTimeScale = FLT_MAX;
+                success = false;
             }
         } else {
             rotation = _desiredRotationalTarget;
@@ -68,7 +71,7 @@ bool ObjectActionTractor::getTarget(float deltaTimeStep, glm::quat& rotation, gl
         linearVelocity = glm::vec3();
         angularVelocity = glm::vec3();
     });
-    return true;
+    return success;
 }
 
 bool ObjectActionTractor::prepareForTractorUpdate(btScalar deltaTimeStep) {
@@ -122,6 +125,8 @@ bool ObjectActionTractor::prepareForTractorUpdate(btScalar deltaTimeStep) {
                 linearTractorCount++;
                 position += positionForAction;
             }
+        } else {
+            return false; // we don't have both entities loaded, so don't do anything
         }
     }