gistfile1.ino

int xPosition = 0;
int yPosition = 0;
int totalStepsCircle = 25; // number steps to complete the circle
int centerX = 500; // half the frame lenght
int centerY = 500; // half the frame lenght
int radius = 250; 
int currentStep = 0;

void setup() {
  // put your setup code here, to run once:

}

void loop() {
  updateCirclePosition();
  
 /*
  - Then just call the motors to update to position xPosition and yPosition
  - Then call run
  - You can easily move this function to processing and just send the commands acorsing to the x and y
  - Take care that if you are not aware when the motor is done,
    when the steps are accomplished, just set some interval, 
    call the update circle the commands every X seconds.
 */
 
}

void updateCirclePosition(){
  if(currentStep > totalStepsCircle) currentStep = 0;
  xPosition = (centerX + radius * cos(2 * PI * currentStep / totalStepsCircle));
  yPosition = (centerY + radius * sin(2 * PI * currentStep / totalStepsCircle));
  currentStep++;
}