Question

I have an image that rotating in a counter clockwise direction. Now, I want it to move in a random direction during or whenever it touch the wall. The problem is I can’t do it, please help me about this matter.

This is my code :

private double x;
private double y;
private double speed;

public void move(long dt)
{
    double dt_s = dt / 1e9;
    double dx = speed * dt_s;
    double dy = speed * dt_s;

    final double right_border = 100;
    final double up_border = 100;
    final double down_border = 0.0;
    final double left_border = 0.0;


    x += dx;

    if (x >= right_border)
    {
        x = right_border;
      if (y >= down_border)
       {               
    y += dy;
       }

    }
    if (y > up_border)
    {
        y = up_border;
        if (x >= left_border)
        {
            speed *= -1;
        }

    }
    if (x <= left_border)
    {
        x = left_border;
        if (y <= up_border)
        {
            y += dy;
        }

    }
    if (y < down_border)
    {
        y = down_border;
        if (x <= right_border)
        {
            speed *= -1;
        }

    }

 }

Answer 1

First you must solve the problem of your class being directionless – you have speed, but your direction is fixed at 45 degree north east (increment x and y the same).

Add direction to your class as follows:

...
private double speed;
private double angle; // in radians - makes math easier

public void move(long dt) {
    ...
    double dx = speed * dt_s * Math.sin(angle);
    double dy = speed * dt_s * Math.cos(angle);
    ...

Now to head in a random direction:

myObject.setAngle(Math.PI * 2 * Math.random()); // Math.PI * 2 = 360 degrees

If hitting a wall, you will have to limit your angle to an angle that’s away from the wall you are hitting. I’ll leave that to you, but it will take the form of:

myObject.setAngle(minAngle + ((maxAngle - minAngle) * Math.random()));