NYUSH2020S_6_arrays.pde

/* IxLab 2020S -  NYU Shanghai
 *  recorded to introduce concepts 
 *  Ideas for exercises to practice: 
 *  make the balls have different size
 *  make the balls appear if you press a key
 *  make them vanish if certain time elapsed
 */


float[] x;        //positions X
float[] y;        //positions Y
float[][] spd;      //speeds: first element is speedX, second speedY
color[] c;           //colors of the balls

int d = 20;
int qty = 50; //how many balls
int t = 255;

void setup() {
  size(500, 500);
  x = new float[qty];
  y = new float[qty];
  spd = new float[qty][2];
  c = new color[qty];

  for (int i=0; i<qty; i++) {
    x[i] = random(width);
    y[i] = random(height);
    spd[i][0] = random(-5, 5);
    spd[i][1] = random(-5, 5);
  }
  noStroke();
}

void draw() {
  background(125);

  for (int i=0; i<qty; i++) {
    x[i]  =  x[i]  + spd[i][0];
    y[i]  =  y[i]  + spd[i][1];

    if ((x[i]  > width-d/2) || (x[i]  < d/2)) {  // x is too big
      spd[i][0] *= -1;
    }
    if ((y[i]  > height-d/2) || (y[i]  < d/2)) {  // x is too big
      spd[i][1] *= -1;
    }

    fill(c[i]);
    ellipse (x[i], y[i], d, d);
  }
}

void mousePressed() {
  for (int i=0; i<qty; i++) {
    c[i] = color(random(0, 255), random(0, 255), random(0, 255), t); //the 4th parameter sets transparency
  }
}

void keyPressed() {
}