This example is for Processing 3+. If you have a previous version, use the examples included with your software. If you see any errors or have suggestions, please let us know.

Sine Cosine.

Linear movement with sin() and cos(). Numbers between 0 and PI*2 (TWO_PI which angles roughly 6.28) are put into these functions and numbers between -1 and 1 are returned. These values are then scaled to produce larger movements.

 
float x1, x2, y1, y2;
float angle1, angle2;
float scalar = 70;

void setup() {
  size(640, 360);
  noStroke();
  rectMode(CENTER);
}

void draw() {
  background(0);

  float ang1 = radians(angle1);
  float ang2 = radians(angle2);

  x1 = width/2 + (scalar * cos(ang1));
  x2 = width/2 + (scalar * cos(ang2));
  
  y1 = height/2 + (scalar * sin(ang1));
  y2 = height/2 + (scalar * sin(ang2));
  
  fill(255);
  rect(width*0.5, height*0.5, 140, 140);

  fill(0, 102, 153);
  ellipse(x1, height*0.5 - 120, scalar, scalar);
  ellipse(x2, height*0.5 + 120, scalar, scalar);
  
  fill(255, 204, 0);
  ellipse(width*0.5 - 120, y1, scalar, scalar);
  ellipse(width*0.5 + 120, y2, scalar, scalar);

  angle1 += 2;
  angle2 += 3;
  
}