Need help with Array intersection.

Programming Questions

Wanaka

Need help with Array intersection.

in Programming Questions • 1 year ago

Hey guys, i have made some balls from an array which are just bouncing around at the moment...I have tried to make them bounce when they intersect with each other, but i have no clue of how to do it. I can manage it when there are only two instances of the ballclass... so please can someone tell me how to make the balls from the same array bounce away from each other?!

Code:

Ball[] ball;
int totalBalls = 0;
int lastMillis = 0;
void setup() {
size(400, 400);
smooth();
// Initialize balls
ball = new Ball[100];
}
void draw() {
background(255);
//timer; display a new ball randomly
if (millis()- lastMillis>random(1000, 3000))
{
ball[totalBalls] = new Ball();
lastMillis = millis();
//add one each time
totalBalls ++;
}
//when all balls have been created, start over
if (totalBalls >= ball.length)
{
totalBalls = 0;
}
//move and display
for (int i = 0; i<totalBalls; i++ )
{
ball[i].movement();
ball[i].display();
}
}
class Ball {
float r; // radius
float x, y;
float xspeed, yspeed;
color c = color(100, 50);
// Constructor
Ball() {
r = random(20, 50);
x = random(width);
y = random(height);
xspeed = 5;
yspeed = 5;
}
//movement
void movement() {
x += xspeed; // Increment x
y += yspeed; // Increment y
// Check horizontal edges
if (x > width || x < 0) {
xspeed *= - 1;
}
// Check vertical edges
if (y > height || y < 0) {
yspeed *= - 1;
}
}
// //bounce function
// void bounce()
// {
// xspeed = xspeed * -1;
// yspeed = yspeed * -1;
// }
// Draw the ball
void display() {
stroke(0);
fill(c);
ellipse(x, y, r*2, r*2);
}
}

Replies(4)

micke85

Re: Need help with Array intersection.

1 year ago

Maybe this can help you ?

http://www.learningprocessing.com/examples/chapter-10/example-10-3/

Wanaka

Re: Need help with Array intersection.

1 year ago

I have done my code with this example, but i dont know how to get it to work with an array.

if (ball1.intersect(ball2)) { // New! An object can have a function that takes another object as an argument. This is one way to have objects communicate. In this case they are checking to see if they intersect.
    ball1.highlight();
    ball2.highlight();
  }
  
  ball1.display();
  ball2.display();
}

here they use two instances of the ballclass...but when you only have an array of the ballclass, u cant make the intersect like that; ball1.intersect(ball2)..

So that's my problem, figuring out how to make it work with the array.

quarks

Re: Need help with Array intersection.

1 year ago

The trick is to ensure that each ball is tested against every other ball just once and avoid testing against itself..

So if you have an array of Ball objects called ball and the ball has an intersect method similar to the one in your last post then the solution for an array is

for(int i = 0; i < ball.length - 1; i++){
for(int j = i + 1; j < ball.length; j++){
if(ball[i].intersect(ball[j]){
// balls have intersected do what needs to be done
}
}
}

Wanaka

Re: Re: Need help with Array intersection.

1 year ago

I have tried your code, but I get the "NullPointerException" - error..I have no clue what to do. I wrote what you posted and also in the method, I wrote; ball[i].bounce(); (so that the ball goes reverse)..and later I also tried to write in ball[j].bounce(); but nothing works..is there something I've missed? my intersect method looks like this;

boolean intersect(Ball b) {
// Objects can be passed into functions as arguments too!
float distance = dist(x, y, b.x, b.y); // Calculate distance
// Compare distance to sum of radii
if (distance < r + b.r) {
return true;
}
else {
return false;
}
}

my bounce method
void bounce()
{
xspeed = xspeed * -1;
yspeed = yspeed * -1;
}