// PolarToCartesian 
// Daniel Shiffman <http://www.shiffman.net> 

float r; 
 
// Angle and angular velocity, accleration 
float theta; 
float theta_vel; 
float theta_acc; 
 
void setup() { 
  size(200,200); 
  framerate(30); 
  smooth(); 
  
  // Initialize all values 
  r = 50.0f; 
  theta = 0.0f; 
  theta_vel = 0.0f; 
  theta_acc = 0.0001f; 
} 
 
void draw() { 
  background(0); 
  // Translate the origin point to the center of the screen 
  translate(width/2,height/2); 
  
  // Convert polar to cartesian 
  float x = r * cos(theta); 
  float y = r * sin(theta); 
  
  // Draw the ellipse at the cartesian coordinate 
  ellipseMode(CENTER); 
  noStroke(); 
  fill(200); 
  ellipse(x,y,16,16); 
  
  // Apply acceleration and velocity to angle (r remains static in this example) 
  theta_vel += theta_acc; 
  theta += theta_vel; 
 
}