From d5c0c200de30a2eddf9fedd7fa09aa7929ddb00a Mon Sep 17 00:00:00 2001
From: Andrew Meadows <andrew@highfidelity.io>
Date: Tue, 27 Jan 2015 15:54:32 -0800
Subject: [PATCH] optimization for when physics engine doesn't step

---
 libraries/physics/src/PhysicsEngine.cpp | 38 ++++++++++++++-----------
 libraries/physics/src/PhysicsEngine.h   |  1 +
 2 files changed, 22 insertions(+), 17 deletions(-)

diff --git a/libraries/physics/src/PhysicsEngine.cpp b/libraries/physics/src/PhysicsEngine.cpp
index dfd28dd8a4..f4aa06e31d 100644
--- a/libraries/physics/src/PhysicsEngine.cpp
+++ b/libraries/physics/src/PhysicsEngine.cpp
@@ -29,23 +29,27 @@ PhysicsEngine::~PhysicsEngine() {
 
 // begin EntitySimulation overrides
 void PhysicsEngine::updateEntitiesInternal(const quint64& now) {
-    // NOTE: the grand order of operations is:
-    // (1) relay incoming changes
-    // (2) step simulation
-    // (3) synchronize outgoing motion states
-    // (4) send outgoing packets
-
-    // this is step (4)
-    QSet<ObjectMotionState*>::iterator stateItr = _outgoingPackets.begin();
-    while (stateItr != _outgoingPackets.end()) {
-        ObjectMotionState* state = *stateItr;
-        if (state->doesNotNeedToSendUpdate()) {
-            stateItr = _outgoingPackets.erase(stateItr);
-        } else if (state->shouldSendUpdate(_numSubsteps)) {
-            state->sendUpdate(_entityPacketSender, _numSubsteps);
-            ++stateItr;
-        } else {
-            ++stateItr;
+    // no need to send updates unless the physics simulation has actually stepped
+    if (_lastNumSubstepsAtUpdateInternal != _numSubsteps) {
+        _lastNumSubstepsAtUpdateInternal = _numSubsteps;
+        // NOTE: the grand order of operations is:
+        // (1) relay incoming changes
+        // (2) step simulation
+        // (3) synchronize outgoing motion states
+        // (4) send outgoing packets
+    
+        // this is step (4)
+        QSet<ObjectMotionState*>::iterator stateItr = _outgoingPackets.begin();
+        while (stateItr != _outgoingPackets.end()) {
+            ObjectMotionState* state = *stateItr;
+            if (state->doesNotNeedToSendUpdate()) {
+                stateItr = _outgoingPackets.erase(stateItr);
+            } else if (state->shouldSendUpdate(_numSubsteps)) {
+                state->sendUpdate(_entityPacketSender, _numSubsteps);
+                ++stateItr;
+            } else {
+                ++stateItr;
+            }
         }
     }
 }
diff --git a/libraries/physics/src/PhysicsEngine.h b/libraries/physics/src/PhysicsEngine.h
index 347f7c2620..67a0076b6c 100644
--- a/libraries/physics/src/PhysicsEngine.h
+++ b/libraries/physics/src/PhysicsEngine.h
@@ -114,6 +114,7 @@ private:
 
     ContactMap _contactMap;
     uint32_t _numContactFrames = 0;
+    uint32_t _lastNumSubstepsAtUpdateInternal = 0;
 };
 
 #endif // hifi_PhysicsEngine_h