Trig

float px, py, px2, py2;

float angle, angle2;

float radius = 50;

float frequency = 2;

float frequency2 = 2;

float x, x2;

​

void setup(){

  size(600, 200);

  background (127);

}

​

void draw(){

​

background (127);

  noStroke();

  fill(255);

  ellipse(width/8, 75, radius*2, radius*2);

  // Rotates rectangle around circle

  px = width/8 + cos(radians(angle))*(radius);

  py = 75 + sin(radians(angle))*(radius);

  fill(0);

​

rect (px, py, 5, 5);

  stroke(100);

  line(width/8, 75, px, py);

  stroke(200);

  // Keep reinitializing to 0, to avoid

  // flashing during redrawing

  angle2 = 0;

  // Draw static curve - y = sin(x)

  for (int i = 0; i< width; i++){

    px2 = width/8 + cos(radians(angle2))*(radius);

    py2 = 75 + sin(radians(angle2))*(radius);

    point(width/8+radius+i, py2);

    angle2 -= frequency2;

  }

  // Send small ellipse along sine curve

  // to illustrate relationship of circle to wave

  noStroke();

  ellipse(width/8+radius+x, py, 5, 5);

  angle -= frequency;

  x+=1;

  // When little ellipse reaches end of window,

  // set the variables back to 0

  if (x >= width-60) {

    x = 0;

    angle = 0;

  }

​

  // Draw dynamic line connecting circular path with wave

  stroke(50);

  line(px, py, width/8+radius+x, py);

​

  // Output calculations to screen

  text("y = sin x", 35, 185);

  text("px = " + px, 105, 185);

  text("py = " + py, 215, 185);

​

​

}