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FrameRate.h

// FrameRate.h
//
/////////////////////////////////////////////////////////////////////////////
//
// Copyright (c) 2002 David Ward
//
/////////////////////////////////////////////////////////////////////////////

#ifndef __FrameRate_h__
#define __FrameRate_h__

// keeps track of framerate
// computes the Steps parameter
// computes RXmax - which controls the maximum rate of zooming in

const double LN2 = log(2.0);

class CFrameRate {
      public:
            CFrameRate() ;
            ~CFrameRate() {};
            void Initialise();
            double Rxmax() const {return m_dRXmax;}
            int Steps() const {return m_iSteps;}
            double Framerate() const {return m_dFr;}
            void Reset(unsigned long Time);
            void NewFrame(unsigned long Time);
            
            // TODO: These two shouldn't be the same thing:
            void SetBitrate(double TargetRate);
            void SetMaxBitrate(double MaxRate);
      private:
            double m_dFr;
            double m_dMaxbitrate;    // the maximum rate of entering information
            double m_dRXmax;         // the maximum zoomin per frame
            int m_iFrames,m_iTime,m_iTime2,m_iSamples;
            int m_iSteps;            // the 'Steps' parameter. See djw thesis.
};
      
inline CFrameRate::CFrameRate() {

 // maxbitrate should be user-defined and/or adaptive. Currently it is not.
#if defined(_WIN32_WCE)
      m_dMaxbitrate=5;
#else
      m_dMaxbitrate=5.5;
#endif

      m_dRXmax=2;  // only a transient effect
      m_iFrames=0;
      m_iSamples=1;

      // we dont know the framerate yet - play it safe by setting it high
      m_dFr=1<<5;

      // start off very slow until we have sampled framerate adequately
      m_iSteps=2000;
      m_iTime=0; // Hmmm, User must reset framerate before starting.
}

inline void CFrameRate::Initialise(void) {
      m_dRXmax=2;  // only a transient effect
      m_iFrames=0;
      m_iSamples=1;

      // we dont know the framerate yet - play it safe by setting it high
      m_dFr=1<<5;

      // start off very slow until we have sampled framerate adequately
      m_iSteps=2000;
      m_iTime=0; // Hmmm, User must reset framerate before starting.
}

inline void CFrameRate::NewFrame(unsigned long Time) 
      // compute framerate if we have sampled enough frames
{
      m_iFrames++;

      if (m_iFrames==m_iSamples) {
            m_iTime2=Time;
            if (m_iTime2-m_iTime < 50) 
                  m_iSamples++;      // increase sample size
            else if (m_iTime2-m_iTime > 80) {
                  m_iSamples--;
                  if (m_iSamples <2)
                        m_iSamples=2;
            }
            if (m_iTime2-m_iTime) {
                        m_dFr=m_iFrames*1000.0/(m_iTime2-m_iTime);
                        m_iTime=m_iTime2;
                        m_iFrames=0;

                  }
            m_dRXmax=exp(m_dMaxbitrate*LN2/m_dFr);
            m_iSteps=m_iSteps/2+(int)(-log(0.2)*m_dFr/LN2/m_dMaxbitrate)/2;

            // If the framerate slows to < 4 then we end up with steps < 1 ! 
            if (m_iSteps==0)
                  m_iSteps=1;

      //    dchar debug[256];
      //          _stprintf(debug,TEXT("fr %f Steps %d samples %d time2 %d rxmax %f\n"),fr,Steps,samples,time2,RXmax);
      //    OutputDebugString(debug);
      
      }
}

inline void CFrameRate::Reset(unsigned long Time)
{
      m_iFrames=0;
      m_iTime=Time;
}

inline void CFrameRate::SetBitrate(double TargetRate)
{
      m_dMaxbitrate = TargetRate;
}


inline void CFrameRate::SetMaxBitrate(double MaxRate)
{
      m_dMaxbitrate = MaxRate;
}



#endif /* #ifndef __FrameRate_h__ */

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