From 164439b3037af5628b381a3526a9ef074030aa17 Mon Sep 17 00:00:00 2001
From: Seth Alves <seth.alves@gmail.com>
Date: Tue, 8 Dec 2015 13:53:39 -0800
Subject: [PATCH] don't enable physics until an entire scene has been received
 from the entity server and until nearby (to MyAvatar) entities are ready

---
 interface/src/Application.cpp | 36 +++++++++++++++++++++++++++++++++--
 interface/src/Application.h   |  2 ++
 2 files changed, 36 insertions(+), 2 deletions(-)

diff --git a/interface/src/Application.cpp b/interface/src/Application.cpp
index c0cfbda15b..4a97fd6275 100644
--- a/interface/src/Application.cpp
+++ b/interface/src/Application.cpp
@@ -195,6 +195,8 @@ static const QString INFO_EDIT_ENTITIES_PATH = "html/edit-commands.html";
 static const unsigned int THROTTLED_SIM_FRAMERATE = 15;
 static const int THROTTLED_SIM_FRAME_PERIOD_MS = MSECS_PER_SECOND / THROTTLED_SIM_FRAMERATE;
 
+static const float PHYSICS_READY_RANGE = 3.0f; // how far from avatar to check for entities that aren't ready for simulation
+
 #ifndef __APPLE__
 static const QString DESKTOP_LOCATION = QStandardPaths::writableLocation(QStandardPaths::DesktopLocation);
 #else
@@ -2905,7 +2907,7 @@ void Application::update(float deltaTime) {
 
     _avatarUpdate->synchronousProcess();
 
-    {
+    if (_physicsEnabled) {
         PerformanceTimer perfTimer("physics");
 
         static VectorOfMotionStates motionStates;
@@ -3893,6 +3895,31 @@ void Application::trackIncomingOctreePacket(ReceivedMessage& message, SharedNode
     }
 }
 
+bool Application::nearbyEntitiesAreReadyForPhysics() {
+    // this is used to avoid the following scenario:
+    // A table has some items sitting on top of it.  The items are at rest, meaning they aren't active in bullet.
+    // Someone logs in close to the table.  They receive information about the items on the table before they
+    // receive information about the table.  The items are very close to the avatar's capsule, so they become
+    // activated in bullet.  This causes them to fall to the floor, because the table's shape isn't yet in bullet.
+    EntityTreePointer entityTree = _entities.getTree();
+    if (!entityTree) {
+        return false;
+    }
+
+    QVector<EntityItemPointer> entities;
+    entityTree->withReadLock([&] {
+        AABox box(getMyAvatar()->getPosition() - glm::vec3(PHYSICS_READY_RANGE), glm::vec3(2 * PHYSICS_READY_RANGE));
+        entityTree->findEntities(box, entities);
+    });
+
+    foreach (EntityItemPointer entity, entities) {
+        if (!entity->isReadyToComputeShape()) {
+            return false;
+        }
+    }
+    return true;
+}
+
 int Application::processOctreeStats(ReceivedMessage& message, SharedNodePointer sendingNode) {
     // But, also identify the sender, and keep track of the contained jurisdiction root for this server
 
@@ -3938,7 +3965,12 @@ int Application::processOctreeStats(ReceivedMessage& message, SharedNodePointer
         });
     });
 
-
+    if (!_physicsEnabled && nearbyEntitiesAreReadyForPhysics()) {
+        // These stats packets are sent in between full sends of a scene.
+        // We keep physics disabled until we've recieved a full scene and everything near the avatar in that
+        // scene is ready to compute its collision shape.
+        _physicsEnabled = true;
+    }
 
     return statsMessageLength;
 }
diff --git a/interface/src/Application.h b/interface/src/Application.h
index ce33f051ef..27df7835e6 100644
--- a/interface/src/Application.h
+++ b/interface/src/Application.h
@@ -395,6 +395,7 @@ private:
     
     bool importSVOFromURL(const QString& urlString);
     
+    bool nearbyEntitiesAreReadyForPhysics();
     int processOctreeStats(ReceivedMessage& message, SharedNodePointer sendingNode);
     void trackIncomingOctreePacket(ReceivedMessage& message, SharedNodePointer sendingNode, bool wasStatsPacket);
     
@@ -564,6 +565,7 @@ private:
     bool _isForeground = true; // starts out assumed to be in foreground
     bool _inPaint = false;
     bool _isGLInitialized { false };
+    bool _physicsEnabled { false };
 };
 
 #endif // hifi_Application_h