From f10a47ed75d6367bf286cc1c095808b674967ff9 Mon Sep 17 00:00:00 2001
From: Robert Osfield <robert@openscenegraph.com>
Date: Tue, 2 Mar 2004 21:37:44 +0000
Subject: [PATCH] From David Fries, changed the Win32 Timer init code across to
 using QueryPerformanceCounter to avoid inaccurate and slow original Sleep
 based code.

---
 src/osg/Timer.cpp | 71 +++++++++++++++++++++++++++++++++++++++++------
 1 file changed, 63 insertions(+), 8 deletions(-)

diff --git a/src/osg/Timer.cpp b/src/osg/Timer.cpp
index a2bdb489f..9bf696b72 100644
--- a/src/osg/Timer.cpp
+++ b/src/osg/Timer.cpp
@@ -47,20 +47,75 @@ const Timer* Timer::instance()
         }
         else
         {
-
-            // use a static here to ensure that the Sleep(..) for 1 sec
-            // is not incurred more than once per app execution.
+            // use a static here to ensure that the time to determine
+            // the cpu frequency is not incurred more than once
+            // per app execution.
             static double _tempSecsPerClick=0.0;
             if (_tempSecsPerClick==0.0)
             {
-                Timer_t start_time = tick();
-                Sleep (1000);
-                Timer_t end_time = tick();
+                // QueryPerformanceCounter under Windows 2000 Service Pack 3
+                // two 2.4 GHz cpus was timed to take about 70 times longer
+                // than the RDTSC assembly instruction sequence, but if
+                // that counter is available we use it to quickly determine
+                // the Time Stamp Counter rate, quickly as in 240 microseconds
+                LARGE_INTEGER frequency;
+                if(QueryPerformanceFrequency(&frequency))
+                {
+                    //#define DEBUG_TIME_OUTPUT 1
+                    LARGE_INTEGER QPCstart, QPCstop,
+                        QPCstartAfter, QPCstopAfter;
+                    Timer_t TSCstart, TSCstop;
+                    double QPCSecsPerClock = 1.0/frequency.QuadPart;
+                    double elapsed, last, current, bound;
 
-                _tempSecsPerClick = 1.0/(double)(end_time-start_time);
+                    QueryPerformanceCounter(&QPCstart);
+                    TSCstart=tick();
+                    QueryPerformanceCounter(&QPCstartAfter);
+
+                    current = 0;
+                    do
+                    {
+                        // store the seconds per clock
+                        last = current;
+                        // read the clocks
+                        QueryPerformanceCounter(&QPCstop);
+                        TSCstop=tick();
+                        QueryPerformanceCounter(&QPCstopAfter);
+                        // average before and after to approximate reading
+                        // both clocks at the same time
+                        elapsed = ((QPCstop.QuadPart+QPCstopAfter.QuadPart)
+                            -(QPCstart.QuadPart+QPCstartAfter.QuadPart))/2.0
+                            *QPCSecsPerClock;
+                        // TSC seconds per clock
+                        current = elapsed / (TSCstop-TSCstart);
+                        // calculate a bound to check against
+                        bound = current/1000000;
+                        // break if current-bound<last && current+bound>last
+                    }while(current-bound>last || current+bound<last);
+                    _tempSecsPerClick = current;
+                    #ifdef DEBUG_TIME_OUTPUT
+                    fprintf(stderr, "current %e, last %e\n",
+                        1.0/current, 1.0/last);
+                    fprintf(stderr, "Total Time %e\n",
+                        (QPCstop.QuadPart-QPCstart.QuadPart)*QPCSecsPerClock);
+                    #endif
+                }
+                #ifndef DEBUG_TIME_OUTPUT
+                else
+                #endif
+                {
+                    Timer_t start_time = tick();
+                    Sleep (1000);
+                    Timer_t end_time = tick();
+
+                    _tempSecsPerClick = 1.0/(double)(end_time-start_time);
+                    #ifdef DEBUG_TIME_OUTPUT
+                    fprintf(stderr, "Sec delay rate %e\n",
+                        1.0/_tempSecsPerClick);
+                    #endif
+                }
             }
             _secsPerTick = _tempSecsPerClick;
-
         }
     }