Ghost/replay system

Unity Engine
1

Hi,

I am trying to create a system that allow to recreate player’s drive path. Vehicle is a rigidbody object with physic, “ghost” is simple transform that interpolates between positions and rotations from drivee path.
How it works now? I check every time step player’s vehicle position and rotation and save it in an array. It looks like this:

	public void mark() {
		time += Time.deltaTime;
		if(time >= TIME_STEP) {
			time = 0;
			interpolations.Add(player.transform.position);
		}
	}

When I read array I try to interpolate between current position and destination point. Code looks like this:

	void readMark() {
		time += Time.deltaTime;
		if(time >= TIME_STEP) {
			time = 0;
			if(index >= (interpolations.Length -1)) {
				index = 0;
			} else {
				index++;
			}
			moveDirection = (interpolations[index] - transform.position).normalized;
			velocity = ((interpolations[index] - transform.position).magnitude / TIME_STEP);
		}
		transform.position += moveDirection * (velocity * Time.deltaTime);
	}

This code works… more or less. More, cus path is right, but less, cus you can notice juttering while moving. Any ideas how it should be done without annoying jittering?

2

Maybe store your last position at TIME_STEP and use Mathf.Lerp to interploate smoothly?

3

I actually take position at TIME_STEP. For example, if TIME_STEP equals 1, that means I take position every second. I tried to make TIME_STEP smaller to have more data, but jittering still exists.

4

Ok, this was easy if you think for a while :smile:.

Update isn’t called with same interval, so I have statement time >= TIME_STEP. And this was a problem, cus first script could save points after undefined time step (bigger or equal to TIME_STEP) and second script could read data after different time step.

I did two coroutines, reader and writer, both waits my TIME_STEP, so now writing and loading points are synchronized with same time intervals.

5

Interpolation is key with stuff like this. You probably want to use linear (“Lerp”), and you want to apply it to both position and rotation. You’ll also need a fairly short timestep, otherwise it’ll still look really floaty.