Error with Serial Communication between Processing and Arduino

I have a sensor which can give information about X and Y position movement, and I want to create a simple interface in which a circle on the screen will move in the same direction as I move the sensor. I use Arduino to send position data (float) through serial communication.

However, the code doesn't seem to work well. The circle I create, sometimes it disappears from the screen, and after a while, it shows up again. Besides, the circle seems to "blink" (I mean it appears/disappears in high frequency) all the time. I'm doubted that the problem is about the buffer, but I'm not so sure. Here is the code I use:

PROCESSING CODE

 // import libraries
import java.awt.Frame;
import java.awt.BorderLayout;
import processing.serial.*;

// Serial port to connect to
String serialPortName = "COM3";


/* SETTINGS END */

Serial serialPort; // Serial port object


void setup() {
  size(900,900);
  noStroke();

    serialPort = new Serial(this, serialPortName, 9600); 
}

byte[] inBuffer = new byte[50]; // holds serial message

void draw() {
      background(0);
  if (serialPort.available() > 0) {
    float[] x= new float[2];
    String myString = "";
      try {
        serialPort.readBytesUntil('\r', inBuffer);
      }
      catch (Exception e) {
      }
      myString = new String(inBuffer);
      String[] nums = split(myString, ' ');
        try {
            x[0] = float(nums[0]);    //X
            x[1] = float(nums[1]);    //Y
        }
        catch (Exception e) {
        }  
      ellipse(x[0]+500, x[1]+500, 70, 70);      //+500 to make the circle in the middle of interface
  }
  }

Serial communication in Arduino:

Serial.print(xf,DEC);        //méthode 1
Serial.print(" ");
Serial.print(yf,DEC);       
Serial.print('\r');

Please help me to find the root cause of this problem. Thank you so much!!