From 181f690bb8865001b8edba9767eea2192c637db3 Mon Sep 17 00:00:00 2001
From: David Rose <david@ddrose.com>
Date: Fri, 7 Dec 2007 02:25:10 +0000
Subject: [PATCH] ClockObject::calc_frame_rate_deviation()

---
 panda/src/grutil/frameRateMeter.cxx |  5 +++--
 panda/src/putil/clockObject.cxx     | 35 +++++++++++++++++++++++++++++
 panda/src/putil/clockObject.h       |  1 +
 3 files changed, 39 insertions(+), 2 deletions(-)

diff --git a/panda/src/grutil/frameRateMeter.cxx b/panda/src/grutil/frameRateMeter.cxx
index 1fa46af613..d97960eb8b 100644
--- a/panda/src/grutil/frameRateMeter.cxx
+++ b/panda/src/grutil/frameRateMeter.cxx
@@ -181,14 +181,15 @@ do_update(Thread *current_thread) {
   _last_update = _clock_object->get_frame_time(current_thread);
 
   double frame_rate = _clock_object->get_average_frame_rate(current_thread);
+  double deviation = _clock_object->calc_frame_rate_deviation(current_thread);
 
   static const size_t buffer_size = 1024;
   char buffer[buffer_size];
 #ifdef WIN32_VC
   // Windows doesn't define snprintf().  Hope we don't overflow.
-  sprintf(buffer, _text_pattern.c_str(), frame_rate);
+  sprintf(buffer, _text_pattern.c_str(), frame_rate, deviation);
 #else
-  snprintf(buffer, buffer_size, _text_pattern.c_str(), frame_rate);
+  snprintf(buffer, buffer_size, _text_pattern.c_str(), frame_rate, deviation);
 #endif
   nassertv(strlen(buffer) < buffer_size);
 
diff --git a/panda/src/putil/clockObject.cxx b/panda/src/putil/clockObject.cxx
index f047d32417..f78e6ff1d9 100644
--- a/panda/src/putil/clockObject.cxx
+++ b/panda/src/putil/clockObject.cxx
@@ -277,6 +277,41 @@ get_average_frame_rate(Thread *current_thread) const {
   }
 }
 
+////////////////////////////////////////////////////////////////////
+//     Function: ClockObject::calc_frame_time_deviation
+//       Access: Published
+//  Description: Returns the standard deviation of the frame times of
+//               the frames rendered over the past
+//               get_average_frame_rate_interval() seconds.  This
+//               number gives an estimate of the chugginess of the
+//               frame rate; if it is large, there is a large
+//               variation in the frame rate; if is small, all of the
+//               frames are consistent in length.
+//
+//               A large value might also represent just a recent
+//               change in frame rate, for instance, because the
+//               camera has just rotated from looking at a simple
+//               scene to looking at a more complex scene.
+////////////////////////////////////////////////////////////////////
+double ClockObject::
+calc_frame_rate_deviation(Thread *current_thread) const {
+  CDStageReader cdata(_cycler, 0, current_thread);
+  if (_ticks.size() <= 1) {
+    return 0.0;
+  } else {
+    double mean = (_ticks.back() - _ticks.front()) / (_ticks.size() - 1);
+    size_t i;
+    double sum_squares = 0.0;
+    for (i = 0; i < _ticks.size() - 1; ++i) {
+      double delta = _ticks[i + 1] - _ticks[i];
+      double diff = (delta - mean);
+      sum_squares += (diff * diff);
+    }
+    double deviation_2 = sum_squares / (_ticks.size() - 1);
+    return sqrt(deviation_2);
+  }
+}
+
 ////////////////////////////////////////////////////////////////////
 //     Function: ClockObject::tick
 //       Access: Published
diff --git a/panda/src/putil/clockObject.h b/panda/src/putil/clockObject.h
index 3b9951638f..6caad2b14e 100644
--- a/panda/src/putil/clockObject.h
+++ b/panda/src/putil/clockObject.h
@@ -108,6 +108,7 @@ PUBLISHED:
   INLINE void set_average_frame_rate_interval(double time);
   INLINE double get_average_frame_rate_interval() const;
   double get_average_frame_rate(Thread *current_thread = Thread::get_current_thread()) const;
+  double calc_frame_rate_deviation(Thread *current_thread = Thread::get_current_thread()) const;
 
   void tick(Thread *current_thread = Thread::get_current_thread());
   void sync_frame_time(Thread *current_thread = Thread::get_current_thread());