Clock() for Frame Independent Animation

[torleif]

Is it safe to use clock()?

A script kiddie tool I used a while ago it simply used ticks (ie, clock()) to do get sub second time. Some research seems to indicate it's bad, it might change if you swap to another computer that fails on a multiple of 66MHz

I want to have a character affected by many forces at once, IE: wind, gravity, weapons and jumping. Traditionally I get the players original position, and then add the time on this. But with these forces, I need to get a small amount of time since last update. Being dead accurate isn't important, but if your game runs twice as slow as it should there are going to be problems. Irrlichts getFPS() has problems, and I want to keep the code cross compatible.

How do you solve this problem?

[hybrid]

Irrlicht has a virtual timer interface which will give you all necessary information.

[B@z]

ISceneManager->getTimer()->getTime()
or get RealTime()

its better to use because you can slow it down (slow mtion) or stop it (pause)

[ehenkes]

but be careful with setTime, because animators use it, too.

[torleif]

Thanks for your replies, Irrlichts timer tends to jump, but I realized such a small jump in time isn't noticeable. It still can be used for animations as long as I don't divide by the difference (newtime-oldtime is often 0):

Code: Select all

endTime = timer->getTime()
main loop{
  // I use this variable to animate stuff 
  difference = timer->getTime() - endTime
  // do stuff here

  // end loop
  endTime = timer->getTime()
}

I was scared off by irrlichts getTimer function because:

Code: Select all

Itimer* timer = device->getTimer();
while(main loop) {
  std::cout << timer->getTime() <<"\n";
}

Would print out:

Code: Select all

120 
120 
120 
120 
120 
160 
160 
160 
160 
160 
160 

The time isn't updated every render loop.

[vitek]

I was scared off by irrlichts getTimer function because:

Code: Select all

Itimer* timer = device->getTimer();
while(main loop) {
  std::cout << timer->getTime() <<"\n";
}

Would print out:

Code: Select all

120 
120 
120 
120 
120 
160 
160 
160 
160 
160 
160 

The time isn't updated every render loop.

The system timer is only so accurate. The real issue is that the loop executes more frequently than the system timer updates. In a real program your main loop will do something that takes up some time, then you won't see the problem.

Assuming the high performance counters are being used, you can check the timer update interval with a call to QueryPerformanceFrequency(). If the counters are not being used, then the GetTickCount() API is used (on windows) and I believe that function is subject to a 15ms update interval.

Travis

[rogerborg]

If you update to the SVN trunk, you'll get a fixed version that uses the HPC on Windows.