Remove object from 2D Array- Processing

Question

I'm creating a simple space invaders game. I'm looking to delete one of the invaders once they are hit by a bullet. The invaders are made up of a 2D array of images and I've tested the collision between the image and the bullet (in an ArrayList) and that works fine. So the game detects a collision, the next step is to delete the correct object that has been hit. I'm a little confused as to how to correctly correspond where the bullet hits to which object it has hit in the 2D array, and then deleting it from the Array and carrying on with the game.

Below is how I created the invader array in setup()

  for(int i=0; i<2; i++){
    for(int j=0; j<4; j++){
        invArray[j][i]= new Taxi(taxiX, taxiY);
        taxiX= taxiX+ 100;
    }
    taxiX=20;
    taxiY= taxiY+ 140;
  }

I then filled the 2D Array with images in draw()

 for(int i=0; i<2; i++){
      for(int j=0; j<4; j++){
        invArray[j][i].update();
        if(invArray[j][i].y>=600){
           invArray[j][i].y= 0;
           invArray[j][i].render();
        }
      }
    }

George Profenza · Accepted Answer · 2017-04-03 18:02:25Z

0

You're using arrays which are fixed size. In theory you might be able to use array helper functions like shorten() and expand(), but you really got watch your counters and array structure. In practice, for a beginner, I would say this is error prone.

It might be simpler(but hackier) to set the array element of the hit invader to null, then simply check if the invader is not null before test collisions/rendering/etc.

e.g. in draw():

for(int i=0; i<2; i++){
      for(int j=0; j<4; j++){
        if(invArray[j][i] != null){
           invArray[j][i].update();
           if(invArray[j][i].y>=600){
              invArray[j][i].y= 0;
              invArray[j][i].render();
           }
         }
      }
    }

Another option is to use an ArrayList which has a dynamic size. e.g.

ArrayList<Taxi> invaders = new ArrayList<Taxi>();

In setup you'd do something similar:

for(int i=0; i<2; i++){
    for(int j=0; j<4; j++){
        invaders.add(new Taxi(taxiX, taxiY));
        taxiX= taxiX+ 100;
    }
    taxiX=20;
    taxiY= taxiY+ 140;
  }

then in draw():

for(int i = 0 ; i < invaders.size(); i++){
    Taxi t = invaders.get(i);
    t.update();
    if(t.y>=600){
       t.y= 0;
       t.render();
    }
    /*
    if(YOUR_HIT_CONDITION_HERE){
        invaders.remove(t);
    }
    */
}

It's a bit tricky to go back and forth between 1D and 2D arrays/indexing at the beginning, but it's not that bad once you get the hand of it.

To convert from 2D x,y to 1D index:

int index = x + y * width;

(where x,y are you counters and width is the width of your grid (number of columns)).

The other way around, 1D index to 2D x,y:

int x = index % width; int y = index / width;

edited Apr 3, 2017 at 18:02

answered Apr 3, 2017 at 11:41

George Profenza

51.9k20 gold badges155 silver badges228 bronze badges

Sign up to request clarification or add additional context in comments.

4 Comments

badprogramming99 Over a year ago

I was thinking of switching over to an ArrayList but wasn't sure how to handle to two rows but I'll try it. Thank you so much!

George Profenza Over a year ago

Feel free to vote and/or mark the answer if it was helpful ;)

badprogramming99 Over a year ago

I've changed everything to an ArrayList now thanks for that :) However the hit detection is off, sometimes it registers and sometimes it does not. For example, the bullets go through the first line of invaders and then hit the second row (the back row). The remove method works for a couple of invaders, after that I'm getting an IndexOutOfBoundsException error for some reason.

George Profenza Over a year ago

It depends how you do the collision detection. It's unclear if the same bullet goes through the first invader, then the second and if it should do that in the first place. I recommend asking a separate question, detailing this aspect

Juan Manuel González Sánchez · Accepted Answer · 2017-04-11 09:24:27Z

0

Try to decouple the hit detection from removing elements from the arraylist, maybe using a flag and removing at the end on the draw loop. Use arraylist.size() as limit of the loop in one part of the code. Maybe that can solve your problem with hit detection, maybe you need a counter.

answered Apr 11, 2017 at 9:24

Juan Manuel González Sánchez

164 bronze badges

Collectives™ on Stack Overflow

Remove object from 2D Array- Processing

2 Answers 2

4 Comments

Comments

Your Answer

Hot Network Questions

Collectives™ on Stack Overflow

2 Answers 2

4 Comments

Comments

Your Answer

Sign up or log in

Post as a guest

Related