Question

What is a good way to get an accurate framerate (frames per second) in native windows opengl c++?

Answer 1

Here’s a timer class I used to use back in the day, in an ATL project. Haven’t done C++ or opengl for awhile, but maybe this will give you some ideas:

Usage

// Put this in your class somewhere
CTimer m_timer;

// Initialize the timer using
m_timer.Init();

// Call this everytime you call draw your scene
m_timer.Update();

// Call this to get the frames/sec
m_timer.GetFPS();

Timer Class

// Timer.h: Timer class used for determining elapsed time and 
//              frames per second.
//
//////////////////////////////////////////////////////////////////////

#ifndef _E_TIMER_H
#define _E_TIMER_H

#pragma once

//////////////////////////////////////////////////////////////////////
// INCLUDES
//////////////////////////////////////////////////////////////////////

#include <windows.h>
#include <stdio.h>
#include <math.h>

//////////////////////////////////////////////////////////////////////
// CLASSES
//////////////////////////////////////////////////////////////////////

class CTimer
{
private:
    //performance timer variables
    __int64       m_i64PerformanceTimerStart;
    __int64       m_i64PerformanceTimerElapsed;

    //multimedia timer variables
    unsigned long m_ulMMTimerElapsed;
    unsigned long m_ulMMTimerStart;

    //general timer variables
    __int64       m_i64Frequency;
    float         m_fResolution;
    bool          m_bPerformanceTimer;

    //FPS variables
    float m_fTime1;
    float m_fTime2;
    float m_fDiffTime;
    float m_fFPS;
    int m_iFramesElapsed;

public:

    //----------------------------------------------------------
    // Name:    CTimer::CTimer
    // Desc:    Default constructor
    // Args:    None
    // Rets:    None
    //----------------------------------------------------------
    CTimer( void )
        : m_fFPS(0.0f), m_fTime1(0.0f), m_fTime2(0.0f), m_fDiffTime(0.0f), m_iFramesElapsed(0)
    {   }

    //----------------------------------------------------------
    // Name:    CTimer::CTimer
    // Desc:    Default destructor
    // Args:    None
    // Rets:    None
    //----------------------------------------------------------
    virtual ~CTimer( void )
    {   }

    //----------------------------------------------------------
    // Name:    CTimer::Init - public
    // Desc:    Initiate the timer for the program
    // Args:    None
    // Rets:    bool:   -true: using performance timer
    //                  -false: using multimedia timer
    //----------------------------------------------------------
    bool Init( void )
    {
        //check to see if we are going to be using the performance counter
        if( QueryPerformanceFrequency( ( LARGE_INTEGER* )&m_i64Frequency ) )
        {
            //we are able to use the performance timer
            m_bPerformanceTimer= true;

            //get the current time and store it in m_i64PerformanceTimerStart
            QueryPerformanceCounter( ( LARGE_INTEGER* )&m_i64PerformanceTimerStart );

            //calculate the timer resolution
            m_fResolution= ( float )( ( ( double )1.0f )/( ( double )m_i64Frequency ) );

            //initialize the elapsed time variable
            m_i64PerformanceTimerElapsed= m_i64PerformanceTimerStart;
        }

        //we cannot use the performence counter, so we'll use the multimedia counter
        else
        {
            //we're using the multimedia counter
            m_bPerformanceTimer= false;

            m_ulMMTimerStart   = timeGetTime( );    //record the time the program started
            m_ulMMTimerElapsed = m_ulMMTimerStart;  //initialize the elapsed time variable
            m_fResolution      = 1.0f/1000.0f;
            m_i64Frequency     = 1000;
        }

        return m_bPerformanceTimer;
    }

    //----------------------------------------------------------
    // Name:    CTimer::Update - public
    // Desc:    Update the timer (perform FPS counter calculations)
    // Args:    None
    // Rets:    None
    //----------------------------------------------------------
    void Update( void )
    {
        //increase the number of frames that have passed
        m_iFramesElapsed++;

        if ( m_iFramesElapsed % 5 == 1 )
          m_fTime1 = GetTime( )/1000;

        else if ( m_iFramesElapsed % 5 == 0 ) 
        {
            m_fTime1 = m_fTime2;
            m_fTime2   = GetTime( )/1000;
            m_fDiffTime= ( float )fabs( m_fTime2-m_fTime1 );      
        }  

        m_fFPS= 5/( m_fDiffTime );



        /*m_fTime2   = GetTime( )/1000;
        m_fDiffTime= ( float )fabs( m_fTime2-m_fTime1 );
        if (m_fDiffTime > 1.0f)
        {
            m_fTime1 = m_fTime2;
            m_fFPS= m_iFramesElapsed / ( m_fDiffTime );
            m_iFramesElapsed = 0;
        }
        */
    }

    //----------------------------------------------------------
    // Name:    CTimer::GetTime - public
    // Desc:    Get the current time since the program started
    // Args:    None
    // Rets:    float: The time elapsed since the program started.
    //----------------------------------------------------------
    float GetTime( void )
    {
         __int64 i64Time;

        //check to see if we are using the performance counter
        if( m_bPerformanceTimer )
        {
            //get the current performance time
            QueryPerformanceCounter( ( LARGE_INTEGER* )&i64Time );

            //return the time since the program started
            return ( ( float )( i64Time - m_i64PerformanceTimerStart )*m_fResolution )*1000.0f;
        }

        //we are using the multimedia counter
        else
        {
            //return the time since the program started
            return ( ( float )( timeGetTime( ) - m_ulMMTimerStart )*m_fResolution )*1000.0f;
        }
    }

    //----------------------------------------------------------
    // Name:    CTimer::GetElapsedSeconds - public
    // Desc:    Get the elapsed seconds since the last frame was drawn.
    // Args:    elapsedFrames:
    // Rets:    float: The time elapsed since the program started.
    //----------------------------------------------------------
    float GetElapsedSeconds(unsigned long elapsedFrames = 1)
    {   return m_fDiffTime;     }

    //----------------------------------------------------------
    // Name:    CTimer::GetFPS - public
    // Desc:    Get the current number of frames per second
    // Args:    None
    // Rets:    float: the number of frames per second
    //----------------------------------------------------------
    inline float GetFPS( void )
    {   return m_fFPS;  }
};

#endif // _E_TIMER_H