Looking for a random direction loop for an object

Question

In CS class we made a simple game using a program called greenfoot. This game was much like the game "Frogger" if you are familiar. I am now practicing on my own, and want to make a game similar. My new game is going to be somewhat close to PacMan. The game I made before I control a rocket ship that needs to reach the top of the screen. Meanwhile, I have made randomly selected sizes and speeds for rectangles bouncing of the walls. But, I want to make it more interesting for my new game. I want a loop for these objects that create a random direction when it is first complies, and bounce of the walls and continue on in that direction, much like that famous screen saver that bounces around. Here is my code for the first game, is it anything like this? So ultimately my question is, how do I write a loop for a random direction.

public boolean canMoveRight() 
{
  if ( getX() + 1 < getWorld().getWidth() ) 
    return true;
  else
    return false;
}
public boolean canMoveLeft() 
{
  if ( getX() - 1 > 0 )
    return true;
  else 
    return false;
}

public void moveRight()
{
       setLocation( getX() + speed, getY() );
}
public void moveLeft() 
{
      setLocation ( getX() - speed, getY()  );
}  

    public void act() 
    {
    if (right==true) 
    {
    if (canMoveRight() )
    {
       moveRight();
    }
    else
    {
       right = false;
    }
  }
  else 
  {
     if( canMoveLeft() )
             moveLeft();
     else
            right = true;
  }
}

Yes, this is working for my first game. But, I want a new loop that is random, instead of starting on the left, and going right every time. — New2.java, Apr 10 '12 at 14:45
This may be a bit unrelated but I believe this is close to the pokemon-styled gameplay. You would be better off setting collision flags for the tiles. That will enable dynamic areas. — , Apr 10 '12 at 14:54
Hm, okay. I am fairly new to Java, I do no think I have learned about collision flags yet. — New2.java, Apr 10 '12 at 14:57

score 0 · Answer 1 · answered Apr 10 '12 at 14:57

Define a Direction enum e.g. Up, RightUp,Right... LeftUp.

Use random to pick one. Direction translates to a change in position of dX,dX, so with a movement step of say 1 pixel UpLeft is -1,-1 (origin top left !) then in your loop simply add dx to X and dy to Y.

score 0 · Answer 2 · answered Apr 10 '12 at 14:57

0

Something along these lines, I guess, would work:

Random random = new Random();

int direction = random.nextInt(1); // gives 0 or 1 randomly
if (direction == 0) {
   // move left
} else {
   // move right
}

answered Apr 10 '12 at 14:57

maksimov

5,792
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Why not simply `if(new java.util.Random().nextBoolean())` or `if(Math.random() >= 0.5)`? – mmaag Apr 10 '12 at 16:49
@IchBinKeinBaum yep, nicer, by all means. However, since New2.java is new to Java :) and is using Greenfoot, I think, it may be better if code is more or less self-explanatory, rather than an efficient one-liner. – maksimov Apr 10 '12 at 20:54

twain249 · Answer 3 · 2012-04-10T15:53:17.537

Are you looking for something likes this?

int horz = ((Math.random() * 10) % 10) + 1; //I just choose 10 at random
int vert = ((Math.random() *10) % 10) + 1;
//You can use another random number to choose to negate either horz or vert if you want
//You can also use random numbers to define the start location.

public boolean canMoveHorz() 
{
  if ( (getX() + horz < getWorld().getWidth() && horz > 0) || (getX() + horz > 0 && horz < 0)) 
    return true;
  else
    return false;
}
public boolean canMoveVert() 
{
  if ( (getY() + vert > 0 && vert < 0) || (getY() + vert < getWorld().getHeight() && vert > 0))
    return true;
  else 
    return false;
}


public void act() {
   if(!canMoveHorz()) {
       horz *= -1;
   }

   if(!canMoveVert()) {
       vert *= -1;
   }

   setLocation(getX() + horz, getY() + vert);
}

This will require some tweaking but what it does is choose 2 random numbers that dictate the speed (vertically and horizontally) for the object. Then it moves the object in those directions until it reaches the edge of the World at which point it negates the speed so the object will move the opposite direction. This is not the same as a true bounce off the walls because I don't do anything with the angle of the hit to determine the angle of the bounce but this should be able to get you started. If you want a more realistic bounce you'll have to do some geometric calculations.

Yes! Thank you this looks right. I will change the things that need to be changed, and I'm sure it will work. Thank you! — New2.java, Apr 10 '12 at 15:53

Looking for a random direction loop for an object

3 Answers3