Animating an object between two points

[Jj Hill]

Hello all, I'm making a game where you have to order troops around, meaning click on the destination, click on the soldier, and the soldier moves to the destination. I am having problems with the animation part, I have already figured out the MouseListener and graphics stuff. I know that you are supposed to use y = mx + b, m = y2 - y1/x2 - x1 and y - y1 = m(x - x1), but don't know how to implement this into my application, and I have been working on this for a long time with no success (hey, I'm in middle school, and I taught myself). I have a game class that contains the listeners, and a UserUnit class that contains the actual moveTo() method. Assume that I've got everything else figured out, if I don't I'll ask. Any help is appreciated, and thanks in advance.

[Stephan van Hulst]

Well, an animation is a function of distance over time. At time "t" you want to know distance "d" from the starting point. So you need to think of a function that determines this.

If you have a "begin" point and an "end" point, then the "total" distance to be traveled is end - begin. If you want to travel from begin to end in a period of time "duration", then d = distance / duration * t

private Point moveLinear(Point from, Point to, long duration, long time) {
  if (time > duration)
    time = duration;
    
  double x = to.getX() - from.getX(); // horizontal distance after duration
  double y = to.getY() - from.getY(); // vertical distance after duration

  // finish method
}

...

  Point from = ...
  Point to = ...
  long duration = 5000;
  long start = System.currentTimeMillis();

  for (long time = 0; time < duration; time = System.currentTimeMillis() - start) {
    Point here = moveLinear(from, to, duration, time);
    // update screen with 'here'
  }

[Rob Spoor]

Except you need to use a javax.swing.Timer in order for the Event Dispatcher Thread to be able to do the repainting in between. If you use a loop like that, only the last movement will be seen.

[Stephan van Hulst]

Yes, I agree with Rob. My for loop was a poor example.

[Jj Hill]

I've actually found a way to use Thread.sleep(), but thanks for the advice.

[Jj Hill]

I know how to animate it, my problem is the actual movement.

[Stephan van Hulst]

What do you mean by actual movement?