Teensy Mouse Code

int ledPin = 0;                  // Led Output pin
int inPins[] = {0,1,2,3};        // Analog Input pins for the 4 photoresistors
int bufferPast[] = {0,0,0,0};    // Motion detector buffer. Not used.
int bufferPresent[] = {0,0,0,0}; // Motion detector buffer. Not used.
int calibated[] = {0,0};         // Store the X and Y bias. => Ambiant light noise. used to remove the light noise in the reading.
int is_calibrated = 0;           // 0 = Not calibrated yet. 1 = calibrated. Set to 1 by the calibrate() function.

void setup()   {
  pinMode(ledPin, OUTPUT);
  Serial.begin(9600);
}

void loop() {
  if (is_calibrated == 0) {
    blinkIt(5,200);                       // Blink the led 5 time slowly to let the user know the calibration is going to start
    Serial.println("---------------");
    Serial.println("Calibrating...");
    digitalWrite(ledPin, HIGH);           // light the LED
    calibrate();                          // Calibrate the sensor. The X and Y bias are stored in calibated[]
    Serial.println("Calibration Done!");
    Serial.print("x bias:");
    Serial.print(calibated[0]);
    Serial.print("\t");
    Serial.print("y bias:");
    Serial.print(calibated[1]);
    Serial.println("");
    Serial.println("---------------");
    blinkIt(10,100);                      // Blink 10 time fast to let the user know the calibration is done
  } else {
    digitalWrite(ledPin, HIGH);           // Light the LED
    Serial.print(x_vector_motion());
    Serial.print(";");
    Serial.print(y_vector_motion());
    Serial.println("");
    Mouse.move(x_vector_motion()/10, y_vector_motion()/10);  // Move the mouse according to the sensor's reading. Values divided by 10 to reduce the speed.
    delay(20);
  }
}

// Blink n times with a delay of d ms
void blinkIt(int n, int d) {
  for (int i=0;i<n;i++) {
    digitalWrite(ledPin, HIGH);
    delay(d);
    digitalWrite(ledPin, LOW);
    delay(d);
  }
}

/*
To calibrate:
Sum the X and Y vectors over a few loops, and get the average vector.
This allows to get the X and Y bias of the ambient location.
Then substract this bias from the X and Y vectors when using the sensors.
*/
void calibrate() {
   int x_t = 0;
   int y_t = 0;
   int loops = 100;
   for (int i=0;i<loops;i++) {
     x_t += x_vector_motion();
     y_t += y_vector_motion();
     delay(50);
   }
   calibated[0] = x_t/loops;
   calibated[1] = y_t/loops;
   is_calibrated = 1;
}

// Motion detection function. return 0 for no motion and up to 1023 for motion, depending on the intensity of the light changing. really sensitive!
unsigned int motion(int n) {
  int value = analogRead(inPins[n]);
  bufferPresent[n] = value-bufferPast[n];
  if (bufferPresent[n] < 0) {
    bufferPresent[n] = -bufferPresent[n];
  }
  bufferPast[n] = value;
  return (unsigned int) bufferPresent[n];
}

// return the raw reading of a photoresistor (0 to 1023)
unsigned int raw_motion(int n) {
  int value = analogRead(inPins[n]);
  return (unsigned int) value;
}


/* Vectors:
Create an average between 2 vectors to get a stable reading.
*/
int x_vector_motion() {
  int vector1 = raw_motion(inPins[0])-raw_motion(inPins[1]);
  int vector2 = raw_motion(inPins[2])-raw_motion(inPins[3]);
  return ((vector1+vector2)/2)-calibated[0];
}

int y_vector_motion() {
  int vector1 = raw_motion(inPins[0])-raw_motion(inPins[2]);
  int vector2 = raw_motion(inPins[1])-raw_motion(inPins[3]);
  return ((vector1+vector2)/2)-calibated[1];
}