fix(Interaction): ensure undroppable objects cannot be dropped

If the Interactable Object is set as `isDroppable = false` then it
should not be able to drop the object by the joint breaking or
the object/controller distance being too far. It should also not
drop if the controller is disabled but it will drop if the
Interactable Object is disabled.

The way the prevent drop works on controller disable is by storing
a reference to the grabbed object then auto grabbing it again
when the controller is re-enabled.

Assets/VRTK/Scripts/VRTK_InteractGrab.cs

@@ -57,6 +57,7 @@ public class VRTK_InteractGrab : MonoBehaviour
         private VRTK_ControllerEvents controllerEvents;
         private int grabEnabledState = 0;
         private float grabPrecognitionTimer = 0f;
+        private GameObject undroppableGrabbedObject;
 
         public virtual void OnControllerGrabInteractableObject(ObjectInteractEventArgs e)
         {
@@ -127,6 +128,17 @@ private void OnEnable()
                 return;
             }
 
+            if (undroppableGrabbedObject && !undroppableGrabbedObject.GetComponent<VRTK_InteractableObject>().IsGrabbed())
+            {
+                undroppableGrabbedObject.SetActive(true);
+                interactTouch.ForceTouch(undroppableGrabbedObject);
+                AttemptGrab();
+            }
+            else
+            {
+                undroppableGrabbedObject = null;
+            }
+
             GetComponent<VRTK_ControllerEvents>().AliasGrabOn += new ControllerInteractionEventHandler(DoGrabObject);
             GetComponent<VRTK_ControllerEvents>().AliasGrabOff += new ControllerInteractionEventHandler(DoReleaseObject);
 
@@ -135,6 +147,17 @@ private void OnEnable()
 
         private void OnDisable()
         {
+            if (undroppableGrabbedObject)
+            {
+                if (undroppableGrabbedObject.GetComponent<VRTK_InteractableObject>().isDroppable)
+                {
+                    undroppableGrabbedObject = null;
+                }
+                else
+                {
+                    undroppableGrabbedObject.SetActive(false);
+                }
+            }
             ForceRelease();
             GetComponent<VRTK_ControllerEvents>().AliasGrabOn -= new ControllerInteractionEventHandler(DoGrabObject);
             GetComponent<VRTK_ControllerEvents>().AliasGrabOff -= new ControllerInteractionEventHandler(DoReleaseObject);
@@ -252,7 +275,7 @@ private void CreateJoint(GameObject obj)
                 }
                 controllerAttachJoint = tempSpringJoint;
             }
-            controllerAttachJoint.breakForce = objectScript.detachThreshold;
+            controllerAttachJoint.breakForce = (objectScript.isDroppable ? objectScript.detachThreshold : Mathf.Infinity);
             controllerAttachJoint.connectedBody = controllerAttachPoint;
         }
 
@@ -489,6 +512,8 @@ private void AttemptGrabObject()
                     initialGrabAttempt = GrabInteractedObject();
                 }
 
+                undroppableGrabbedObject = (grabbedObject && grabbedObject.GetComponent<VRTK_InteractableObject>() && !grabbedObject.GetComponent<VRTK_InteractableObject>().isDroppable ? grabbedObject : null);
+
                 if (grabbedObject && initialGrabAttempt)
                 {
                     var rumbleAmount = grabbedObject.GetComponent<VRTK_InteractableObject>().rumbleOnGrab;

Assets/VRTK/Scripts/VRTK_InteractableObject.cs

@@ -766,7 +766,7 @@ private void ChangeColor(Dictionary<string, Color[]> colors)
 
         private void CheckBreakDistance()
         {
-            if (trackPoint)
+            if (trackPoint && isDroppable)
             {
                 float distance = Vector3.Distance(trackPoint.position, originalControllerAttachPoint.position);
                 if (distance > (detachThreshold / 1000))