danielExample

/*
 * Creative Coding
 * Week 3, 04 - spinning top: curved motion with sin() and cos()
 * by Indae Hwang and Jon McCormack
 * Copyright (c) 2014 Monash University
 *
 * This sketch is the first cut at translating the motion of a spinning top
 * to trace a drawing path. This sketch traces a path using sin() and cos()
 *
 */

int num = 5;  // the number of spinning tops
float[] x = new float [num];
float[] y = new float [num];      // current drawing position
float[] dx = new float [num];
float[] dy = new float [num];
float rad;       // radius for the moving hand

void setup() {
  size(500, 500);
  background(0);
  for (int i=0; i<num; i++) {
    float val = 2; //  value for the max/min value of the increments
    x[i]= random(width); // initial horizontal starting point
    y[i]= random(height); // initial vertical starting point
    dx[i] = random(-val, val); // x-increments
    dy[i] = random(-val, val); // y-increments
  }
}


void draw() {
  // blendMode(BLEND); .-> not needed, it's the default
  fill(0, 20); // I would increase the alpha to 15 in order not to have 'smears', except if that's what you want ;)
  rect(0, 0, width, height);
  rad = radians(frameCount);
  for (int i=0; i<num; i++) {
    spinningTop(i, x[i], y[i], dx[i], dx[i]);
  }
}

void spinningTop(int i, float _x, float _y, float _dx, float _dy) {
  // calculate new position
  x[i] += dx[i];
  y[i] += dy[i];
  float max = 1.5;
  float min = 0.5;

  //When the shape hits the edge of the window, it reverses its direction and changes velocity
  if (x[i] > width-100 || x[i] < 100) {
    dx[i] = dx[i] > 0 ? -random(min, max) : random(min, max);
  }

  if (y[i] > height-100 || y[i] < 100) {
    dy[i] = dy[i] > 0 ? -random(min, max) : random(min, max);
  }

  float bx = x[i] + 100 * sin(rad);
  float by = y[i] + 100 * cos(rad);
  fill(180);

  float radius = 100 * sin(rad*0.1);
  float handX = bx + radius * sin(rad*3);
  float handY = by + radius * cos(rad*3);

  stroke(255, 50);
  line(bx, by, handX, handY);
  ellipse(handX, handY, 2, 2);
}