Easing in Java with Slick2D

Question

I am trying to make an object ease in and out.

But when I render this it works well but I always get another object behaving directly opposite to the other.

So when the object is heading up, the "ghost" object will be directly opposite heading down. It gives a rather weird screen tearing effect. I've tried turning on vsync but that seemed to make it worse. The object is a slick2d rectangle. It also has the habit of completely disappearing for a few seconds or even permanently turning into a straight line without me every changing its dimensions. This is the update code.

   @Override
public void update(GameContainer gc, StateBasedGame game, int delta) throws SlickException {
    // TODO Auto-generated method stub

    Input i=gc.getInput();
    d=2000/delta;
    if(i.isKeyDown(Input.KEY_DOWN)){
        if(frames<d)
        frames++;

        if(frames==1)b=hele.getY();
        hele.setY(Quad.easeInOut(frames, b, 720-b-50, d));//the 50 is the size of the sprite
        //c+=10;
    }
    else if(i.isKeyDown(Input.KEY_UP)){
        if(frames<d)
        frames++;

        if(frames==1)b=hele.getY();
        hele.setY(Quad.easeInOut(frames, b, -b, d));

    }



}

The ease in out formulas can be found here on github.

I have the frames var reset once the key is released elsewhere. I am trying to make the sprite behave like a helicopter. If you have any idea how to make it more helicopter like, please share your knowledge!

Answer 1

I seem to have found the problem, updating d with the delta every update causes the screen tear! Keeping it constant will solve the problem.

Instead of using a frame count I used a delta timer instead...

if(elapsedtime<d)
                elapsedtime+=delta;

that keeps track of the time using the delta and for every place I used frames, I replaced with the elapsed time.

if(frames==1){b=getCBox().getY();}
            getCBox().setY(Bounce.easeOut(elapsedtime, b, 720-b-getCBox().getHeight(), d));

However, I still used the frame count to identify the first update for the delta isn't always reliable.

The full source can be found on git here: https://bitbucket.org/BallisticBlaze/helirush-game/

Hope this helps anyone.