How do I have objects in an ArrayList collide with one another?

theZetoranian

I'm trying to make a relatively simple little project for fun. In it, you can click your mouse to have a circle appear. That circle will grow until it collides with a wall or another circle, then shrink. You can keep clicking in different places to add new circles. Unfortunately, I can get everything but the circle-to-circle collision to work.

Here is my code:

ArrayList<Circle> circleArray = new ArrayList<Circle>();
int circleCount = 0;

void setup()
{
  size(300, 300);
}

void draw()
{
  background(0);

  for (int i = 0; i < circleCount; i++)
  {
    circleArray.get(i).display();
    circleArray.get(i).update();
    circleArray.get(i).collideWall();

    //for (int j = i+1; j < circleCount; j++)
    //{
    //  circleArray.get(i).collideCircle(circleArray.get(i));
    //}
  }
}


class Circle
{
  int x, y;
  int circumference;
  int radius;
  int growSpeed;
  boolean isGrowing;
  color col;

  Circle(int tempX, int tempY)
  {
    x = tempX;
    y = tempY;

    circumference = 10;
    radius = circumference/2;
    growSpeed = 1;
    isGrowing = true;
    col = color(random(100, 255), random(100, 255), random(100, 255));
  }

  void display()
  {
    // Draw circle:
    noStroke();
    fill(col);
    ellipse(x, y, circumference, circumference);
  }

  void update()
  {
    // Alternate growing and shrinking:
    if (isGrowing)
      circumference += growSpeed;
    else
      circumference -= growSpeed;

    // Redefine radius:
    radius = circumference/2;
  }

  void collideWall()
  {
    // Wall collision detection:
    if (radius > dist(x, y, x, 0) || radius > dist(x, y, x, height)
     || radius > dist(x, y, 0, y) || radius > dist(x, y, width, y))
      isGrowing = false;
    else if (circumference < 20)
      isGrowing = true;
  }

  void collideCircle(Circle other)
  {
    // Other circle collision detection:
    if (radius + other.radius > dist(x, y, other.x, other.y))
      isGrowing = false;
    else if (circumference < 20)
      isGrowing = true;
  }
}


void mouseClicked()
{
  circleArray.add(new Circle(mouseX, mouseY));
  circleCount++;
}

GoToLoop

http://www.JeffreyThompson.org/collision-detection/circle-circle.php

theZetoranian

I think I'm having more of an issue with the objects interacting within the ArrayList, rather than the collision itself.

Also, I'm struggling to see why if (radius + other.radius > dist(x, y, other.x, other.y)) doesn't work for detecting circle collisions by itself. Why use sq()?

mlandry

you need a nested loop to check collision with every other circle. In your code your checking collision with the same element of your arraylist.

GoToLoop

http://studio.SketchPad.cc/sp/pad/view/ro.989GaZC5t7EkE/latest

kaskus

you need a nested loop to check collision with every other circle. In your code your checking collision with the same element of your arraylist.

is it possible to check collision when we use multiple arraylist?