Object movement with different time scale

Question

Hi everyone,

I am making a top down game in 2d where the player is a car. If you press the right mouse button, the car will "jump" to a certain height which is implemented by increasing the y pos with a height delta that gives the illusion that the car is jumping. This is how it is implemented:

bodyTransform.position = new Vector3(bodyTransform.position.x, bodyTransform.position.y + heightDelta, bodyTransform.position.z);

I am now implementing a feature where, if you press the spacebar, the game will be in slow motion. I implemented this by just reducing the timescale of the game until a value let's say 0.3f.

In slow motion, the normal movement of the car is slowed down, but when I jump, the car just jumps at normal speed.

I tried to multiply the "heightDelta" variable with the "Time.deltaTime" which worked fine for the normal movement, but for jumping, the normal speed is kept and it's only reducing the height of the jump since "Time.deltaTime" is lower when the timescale is lower.

I am doing the movement of the car in the Update function because the movement in slow motion is much smoother than in FixedUpdate

Does anyone have an idea how can I implement the slow motion for the jump?

Any clue would be a great help.

Thank you very much
Ricardo

Answer 1

Hi Everyone,

I have managed to found the solution if this can help anyone in the same situation.

Basically I knew that I had to relate the heightDelta with the the Time.DeltaTime somehow, but if I multiply it directly in the instruction above (in the position update), the car when in slow motion will just jump lower as the Time.DeltaTime is smaller with a smaller Time.TimeScale.

The solution was to use the Time.DeltaTime as I am calculating the heightDelta. To calculate the jump trajectory I am using a parabolic equation like:

h = -t^2 + (ti+tf)*t - ti*tf + h0 where (ti,h0) is the initial jump height and time instant.
Let's consider that the car is jumping from the current car position and we start to measure time from the instant we jump, so we can consider (ti,h0) = (0,0). The tf is the duration of the jump we want. With this we endup with: h = -t^2 + tf*t.

Refer to this page where I found similar information: https://answers.unity.com/questions/1113304/how-can-make-my-player-to-jump-like-parabola.html

From this point we can simply replace t by the current Time.DeltaTime to get the height value.

As the car position is being calculated by using the current position itself, I cannot use the height directly coming from the above equation because we will be always adding positive values which will make the car only go up but will not go down.
What we need to do is to calculate the heightDelta that will be result from recursively subtracting the previous from the current height: heightDelta = h(n) - h(n-1)

With this we can use different time scales and still mantain the same behaviour when jumping.

Object movement with different time scale

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