CODEWITHSUNDEEP
javamathgame-physics
TameHog
TameHog

Reputation: 950

Regulating step speed in game

I am developing a game and I need to create a method to create a movement. What it needs to do is take x y and target x y values and create a float[] with the movement inside of it defined to a certain time. The movement will be used every frame for a certain amount of frames until it has reached the target in a specific time. Here is what I have so far.

public void calculateRoute(int time) {
    if(x > tx){
        movement[0] = -((x - tx) / time);
    }else if(x < tx){
        movement[0] = ((tx - x) / time);
    }else if(x == tx){
        movement[0] = 0;
    }

    if(y > ty){
        movement[1] = -((y - ty) / time);
    }else if(y < ty){
        movement[1] = ((ty - y) / time);
    }else if(y == ty){
        movement[1] = 0;
    }
}

The problem with this is that the farther the target, the quicker the movement is. I want to have the movement regulating to a certain speed but still reach its target. Basically I need to calculate the time variable to a speed that will always be the same, no matter the distance. I tried this with setting the movement to 1 but it would miss its target since x could be 500, and the y could be 700. It would end up being x = 700, y = 700. Any help is appreciated! :)

Also some sample code would be nice!

Upvotes: 0

Views: 118

Answers (2)

jefflunt
jefflunt

Reputation: 33954

Maybe what you're asking is, given:

  • a distance between point A and point B
  • a fixed distance per step let's call this stepSize

You want to have in a float []:

One element for every step it will take to travel distance, one stepSize at a time. So:

stepSize = speed / 60.0;   // 60 fps
stepCount = distance / stepSize;

Then a for loop that goes from 0 to stepCount-1, moving stepSize distance on each step.

I don't know what you need a float[] for in that case. If your step size doesn't evenly divide the distance you need to travel, and on the last step you've overshot you're target a bit, then on the last step simply set the (x, y) to the target (x, y)

Upvotes: 0

jefflunt
jefflunt

Reputation: 33954

Some things to consider:

  1. In today's multi-core, multi-tasking computers you cannot reliably predict how much time will elapse between each rendered frame or each logic/physics/AI update.
  2. As you've discovered with your solution, your speed calculation is based on distance, when it needs to be some units moved per unit of time (perhaps pixels/second, or blocks/second - whatever unit of measure makes sense in your game).
  3. When you're moving things around in your world, it's often best to measure the time elapsed since the last time you moved things around, and then multiply the time elapsed by your speed, because speed*time=distance moved

If you're using a game engine, which would be a really good idea because this is a solved problem, they will provide some kind of "delta" time that tells you how much time has elapsed since the last logic/physics/AI update. You can use that value.

Upvotes: 1

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