# Rendering correctly according to time

OK, here is the case:

I am currently using the OpenInventor libraries for C++, and i want to draw a scene where something happens, e.g. a person walking.

I know that it takes 1 second for a person to take a step forward, because i have coordinate files that tell me the exact position of the limbs at which times. The coordinates are stored on a fileformat which i read into C++ and convert into translations on the person, using the Inventor libraries.

THe problem is the following; i do not want the scene to be rendered too fast. it is important that when i render, it takes exactly one second for the person to take that step.

I want the highest framerate possible at all times in the animation. How do i find out how many fps i can get at a particular state of the scene? Given ofc. the resolution an color depth of the scene to be rendered.

God, this is confusing. I’m not even sure that i understood what i just wrote here Some help or hints to how i can do this would be greatly appreciated;)

• hulapupp

The standard way most games and apps do this is to use the time delta from the previous frame. (some use the average of the last x frames) This is usually clamped to prevent huge time deltas. (framerate spikes can occur depending on what you are doing)

An interpolation from the previous time delta usually works well.
Simple example:

``````static DWORD nowPrevious = GetTickCount();
static DWORD smoothDelta = 0;

#ifndef LIRP
#define LIRP(X,Y,A) ((1.0f-(A))*(float)(X)) + ((A)*(float)(Y))
#endif

DWORD now = GetTickCount();
DWORD nowDelta = now - nowPrevious;
nowPrevious = now;

if (smoothDelta)
smoothDelta = LIRP(smoothDelta, nowDelta, 0.2f);
else
smoothDelta = nowDelta;
``````

smoothDelta now has a smoothed value for the number of milliseconds since the last time the code was executed.
Convert smoothDelta to seconds:-
float secs = float(smoothDelta)/1000.0f;

There are better timer functions than GetTickCount, such as QueryPerformanceCounter…but they involve a bit more work.