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+/************************************************************************************
+
+Filename    :   CAPI_FrameLatencyTracker.h
+Content     :   DK2 Latency Tester implementation
+Created     :   Dec 12, 2013
+Authors     :   Volga Aksoy, Michael Antonov
+
+Copyright   :   Copyright 2014 Oculus VR, LLC All Rights reserved.
+
+Licensed under the Oculus VR Rift SDK License Version 3.2 (the "License"); 
+you may not use the Oculus VR Rift SDK except in compliance with the License, 
+which is provided at the time of installation or download, or which 
+otherwise accompanies this software in either electronic or hard copy form.
+
+You may obtain a copy of the License at
+
+http://www.oculusvr.com/licenses/LICENSE-3.2 
+
+Unless required by applicable law or agreed to in writing, the Oculus VR SDK 
+distributed under the License is distributed on an "AS IS" BASIS,
+WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+See the License for the specific language governing permissions and
+limitations under the License.
+
+************************************************************************************/
+
+#ifndef OVR_CAPI_FrameLatencyTracker_h
+#define OVR_CAPI_FrameLatencyTracker_h
+
+#include <OVR_CAPI.h>
+#include <Kernel/OVR_Timer.h>
+#include <Extras/OVR_Math.h>
+#include <Util/Util_Render_Stereo.h>
+#include "CAPI_FrameTimeManager3.h"
+
+namespace OVR { namespace CAPI {
+
+
+//-------------------------------------------------------------------------------------
+// ***** FrameLatencyData
+
+// This structure contains the timing data for each frame that is tracked by the
+// latency tester.
+
+struct FrameLatencyData
+{
+    uint8_t DrawColor;           // Red channel color value drawn for the latency tester quad for this frame
+    double PresentTime;          // (seconds) Time at which Vsync/Present occurred
+    double RenderIMUTime;        // (seconds) Time when hardware sensors were sampled for render pose
+    double TimewarpIMUTime;      // (seconds) Time when hardware sensors were sampled for timewarp pose
+
+    double TimewarpPredictedScanoutTime; // (seconds) Time at which we expected scanout to start at timewarp time
+    double RenderPredictedScanoutTime;   // (seconds) Time at which we expected scanout to start at render time
+};
+
+
+//-------------------------------------------------------------------------------------
+// ***** OutputLatencyTimings
+
+// Latency timings returned to the application.
+
+struct OutputLatencyTimings
+{
+    double LatencyRender;       // (seconds) Last time between render IMU sample and scanout
+    double LatencyTimewarp;     // (seconds) Last time between timewarp IMU sample and scanout
+    double LatencyPostPresent;  // (seconds) Average time between Vsync and scanout
+    double ErrorRender;         // (seconds) Last error in render predicted scanout time
+    double ErrorTimewarp;       // (seconds) Last error in timewarp predicted scanout time
+
+    void Clear()
+    {
+        LatencyRender      = 0.;
+        LatencyTimewarp    = 0.;
+        LatencyPostPresent = 0.;
+        ErrorRender        = 0.;
+        ErrorTimewarp      = 0.;
+    }
+};
+
+
+//-------------------------------------------------------------------------------------
+// ***** FrameLatencyTracker
+
+// FrameLatencyTracker tracks frame Present to display Scan-out timing, as reported by
+// the DK2 internal latency tester pixel read-back. The computed value is used in
+// FrameTimeManager for prediction. View Render and TimeWarp to scan-out latencies are
+// also reported for debugging.
+//
+// The class operates by generating color values from GetNextDrawColor() that must
+// be rendered on the back end and then looking for matching values in FrameTimeRecordSet
+// structure as reported by HW.
+
+class FrameLatencyTracker
+{
+public:
+    enum { FramesTracked = Util::LT2_IncrementCount-1 };
+
+    FrameLatencyTracker();
+
+    // DrawColor == 0 is special in that it doesn't need saving of timestamp
+    unsigned char GetNextDrawColor();
+
+    void SaveDrawColor(FrameLatencyData const & data);
+
+    void MatchRecord(Util::FrameTimeRecordSet const & r);
+
+    bool IsLatencyTimingAvailable();
+    void GetLatencyTimings(OutputLatencyTimings& timings);
+
+    // Returns time between vsync and scanout in seconds as measured by DK2 latency tester.
+    // Returns false if measurements are unavailable.
+    bool GetVsyncToScanout(double& vsyncToScanoutTime) const;
+
+    void Reset();
+
+protected:
+    struct FrameTimeRecordEx : public Util::FrameTimeRecord
+    {
+        bool             MatchedRecord;
+        FrameLatencyData FrameData;
+    };
+
+    void onRecordMatch(FrameTimeRecordEx& renderFrame,
+                       Util::FrameTimeRecord const& scanoutFrame);
+
+    // True if rendering read-back is enabled.
+    bool                  TrackerEnabled;
+
+    enum SampleWaitType
+    {
+        SampleWait_Zeroes, // We are waiting for a record with all zeros.
+        SampleWait_Match   // We are issuing & matching colors.
+    };
+    
+    SampleWaitType        WaitMode;
+    int                   MatchCount;
+    // Records of frame timings that we are trying to measure.
+    FrameTimeRecordEx     History[FramesTracked];
+    int                   FrameIndex;
+    // Median filter for (ScanoutTimeSeconds - PostPresent frame time)
+    mutable OVR::CAPI::FTM3::MedianCalculator FrameDeltas;
+    double                LatencyRecordTime;
+
+    // Latency reporting results
+    OutputLatencyTimings  OutputTimings;
+};
+
+
+}} // namespace OVR::CAPI
+
+#endif // OVR_CAPI_FrameLatencyTracker_h