High Resolution Timing In Games

I found an article here on gamedev about High Resolution Timing In Games. It can be found here:

http://www.gamedev.net/reference/articles/article753.asp

I downloaded the source code for VC, and got it running fine and I understand how the timer is working more or less. My problem is I don''t understand how to update (a variable for instance) a specific number of times per second using the timer.

The article mentions this:

players.location_x+=players.x_units_per_second*frametime;

Where players.x_units_per_second is supposed to be say the update rate of a variable. So you multiply the update rate of the variable with the time it takes to display a "frame", and you sum up this value...

So I did a little theoretical application of this:

players.x_units_per_second = 4
players.location_x = 0;

players.location_x += 4 * 0.025; // 0 + 4 * 0.025 = 0.1
players.location_x += 4 * 0.070; // 0.1 + 4 * 0.070 = 0.38
players.location_x += 4 * 0.011; // 0.38 + 4 * 0.011 = 0.424
players.location_x += 4 * 0.059; // 0.424 + 4 * 0.059 = 0.66

I just made up some theoretical frame times to multiply with my units per second, and I can''t figure out how I''m supposed to use this to update something a specific number of times per second.

Please help!

i used the code in this article for frame-rate indepentent movement, but it still runs way to fast on my friends ultra-powerful computer, and runs the same no matter how fast i get it. (by turning off vsync i got it to run around 1000fps fullscreen... still speed stayed perfect) how come?

-plasmicsoup

My application before adding a timer for movement using QueryPerformanceTimer and QueryPerformanceFrequency ran smooth as silk, after adding the timer to move in units per second instead of just a constant speed makes the application look terribly chunky, I did not limit the fps or change
anything else I just replaced

float speed = 0.1f

with

float speed = static_cast<float> (1.0f * m_input_timer.Elapsed());

Here is the defintion of the timer:

#ifndef GAME_TIMER_H
#define GAME_TIMER_H
//-----------------------------------------------------------------------------------------------

// game_timer.h

//

// Timer object

//

// Purpose: To provide an interface for timers

//

// Christopher Pisz

// 04/27/04

//-----------------------------------------------------------------------------------------------

#include <windows.h>

class Game_Timer
{
public:
	Game_Timer();
	~Game_Timer();

	void  Start();
	double Elapsed();

private:
	double m_start;

	double GetCurrentCount();
};

#endif // GAME_TIMER_H


//-----------------------------------------------------------------------------------------------

// game_timer.cpp

//

// Timer object

//

// Purpose: To provide an interface for game timers such as frame timer

//

// 

// Christopher Pisz

// 04/27/04

//-----------------------------------------------------------------------------------------------

#include "game_timer.h"

Game_Timer::Game_Timer()
:
m_start( GetCurrentCount() )
{
}

//-----------------------------------------------------------------------------------------------

Game_Timer::~Game_Timer()
{
}

//-----------------------------------------------------------------------------------------------

void Game_Timer::Start()
{
	m_start = GetCurrentCount();
}

//-----------------------------------------------------------------------------------------------

double Game_Timer::Elapsed()
{
	return GetCurrentCount() - m_start;
}

//-----------------------------------------------------------------------------------------------

double Game_Timer::GetCurrentCount()
{
	LARGE_INTEGER time,
		      frequency;

	QueryPerformanceCounter(&time);
	QueryPerformanceFrequency(&frequency);

	return static_cast<double>(time.QuadPart) / frequency.QuadPart;
}

and here is where it is in my render loop

// Enter main event loop

	while(TRUE)
	{
		// Test if there is a message in que, if so get it

		if(PeekMessage(&msg, NULL, 0, 0, PM_REMOVE))
		{
			// Test if this is a quit

			if(msg.message==WM_QUIT)
				break;
			
			// Translate any accelerator keys

			TranslateMessage(&msg);

			// Send the message to window proc

			DispatchMessage(&msg);
		}

		// Main processing loop

		if(m_active)
		{
			// Process input

			ProcessInput();
			m_input_timer.Start();

			// Perform any game logic

			ProcessLogic();
			//m_logic_timer.Start();


			// Render

			//if( m_frame_timer.Elapsed() > 0.0083333333f )

			{
			//	m_frame_timer.Start();

				RenderLoop();
			}
		}
	}

and here is the process input function

void MyGameHost::ProcessInput()
{
	float speed = static_cast<float> (1.0f * m_input_timer.Elapsed());
	//float speed = 0.01f;


	// Rotations /////////////////////////////////////


	// If the ''a'' key is pressed look towards the left

	if(m_keys[65])
		m_camera.Rotate(-speed, D3DXVECTOR3(0.0f, 1.0f, 0.0f));

	// If the ''d'' key is pressed look towards the right

	if(m_keys[68])
		m_camera.Rotate(speed, D3DXVECTOR3(0.0f, 1.0f, 0.0f));
	
	// If the ''w'' key is pressed look up

	if(m_keys[87])
		m_camera.Rotate(-speed, D3DXVECTOR3(1.0f, 0.0f, 0.0f));
	
	// If the ''x'' key is pressed look down

	if(m_keys[88])
		m_camera.Rotate(speed, D3DXVECTOR3(1.0f, 0.0f, 0.0f));

	// If the ''e'' key is pressed roll right

	if(m_keys[69])
		m_camera.Rotate(-speed, D3DXVECTOR3(0.0f, 0.0f, 1.0f));

	// If the ''q'' key is pressed roll left

	if(m_keys[81])
		m_camera.Rotate(speed, D3DXVECTOR3(0.0f, 0.0f, 1.0f));

	// Translations ///////////////////////////////////

	
	// If the ''s'' key is pressed move foward

	if(m_keys[83])
		m_camera.Translate(speed, D3DXVECTOR3(0.0f, 0.0f, 1.0f));

	// If the ''v'' key is pressed move backward

	if(m_keys[86])
		m_camera.Translate(speed, D3DXVECTOR3(0.0f, 0.0f, -1.0f));

	// If the ''z'' key is pressed strafe left

	if(m_keys[90])
		m_camera.Translate(speed, D3DXVECTOR3(-1.0f, 0.0f, 0.0f));
	
	// If the ''c'' key is pressed strafe right

	if(m_keys[67])
		m_camera.Translate(speed, D3DXVECTOR3(1.0f, 0.0f, 0.0f));

	// If the ''r'' key is pressed move up

	if(m_keys[82])
		m_camera.Translate(speed, D3DXVECTOR3(0.0f, 1.0f, 0.0f));

	// If the ''f'' key is pressed move down

	if(m_keys[70])
		m_camera.Translate(speed, D3DXVECTOR3(0.0f, -1.0f, 0.0f));
	
	}

Any ideas on why things became chukified?

I can also provide the full source and .exe from my ftp is anyone wants to see first hand.

Thanks,
Christopher