transmitting x,y coordinates back and forth between arduino and processing

serialxycoord_arduino.pde

int buf = 0;
int xcoordinate = 0;
int ycoordinate = 0;

void setup()
{
    // start serial port at 9600 bps and wait for port to open:
    Serial.begin(115200);
}

void loop()
{
    if (Serial.available() > 0) {
        readCoordinates();
        delay(2);    //9600 baud rate is slower than the arduino clock speed this delay removes problems
        if(Serial.available() == 0){ //this is where you would move the arm to a coordinate I just print them.
            Serial.print(xcoordinate);
            Serial.print(",");
            Serial.println(ycoordinate);
        }
    }
}

/* This function reads serial data and interprets it as
   integer coordinates.  The format should be a string of
   two numbers seperated by only a comma with a new line
   exactly at the end. */
void readCoordinates(){
    byte character = Serial.read(); //read the first byte on serial
    if(character != 10 && character != ','){ //newline(10) and , are special
        buf = buf*10;
        buf += (int)(character - '0'); //these two lines turn the string into an integer
    } else if(character == ','){
        xcoordinate = buf; //after a comma the buffer has the x coordinate
        buf = 0;
    } else {
        ycoordinate = buf; //after a space the buffer has the y coordinate
        buf = 0;
    }
}

serialxycoord_processng.ino

/**
 * Mouse Press. 
 * 
 * Move the mouse to position the shape. 
 * Press the mouse button to invert the color. 
 */

import processing.serial.*; //This allows us to use serial objects
 
Serial port; // Create object from Serial class
int[] x = new int[0];
int[] y = new int[0];
int[] shoulder = new int[0];
int[] elbow = new int[0];
// int[] xylines = new int[0];
float xcoordinate;
float ycoordinate;
String xyline;
float theta1;
float theta2;
boolean elbowup = false; // true=elbow up, false=elbow down
float c2; //is btwn -1 and 1
float s2;
float l1 = 74; //length of links in mm
float l2 = 53;
int width = 700;
int height = 700;

void setup() {
  size(width, height);
  noSmooth();
  fill(126);
  background(102);
  //  println(Serial.list()); //This shows the various serial port option0
  String portName = Serial.list()[0]; //The serial port should match the one the Arduino is hooked to
  port = new Serial(this, portName, 9600); //Establish the connection rate
}

void draw() {}

/* mousePressed() keeps track of mouse clicks
   and sends the coordinates over serial */
void mousePressed() {
  stroke(255);
  ellipse(mouseX,mouseY,5,5);
  if(inbounds(mouseX, mouseY)) {
      mapCoordinates(mouseX, mouseY); //get adjusted coordinates
      getAngles(xcoordinate, ycoordinate); //change coordinates to angles
      sendAngles(); //send the angles over serial
      shoulder = append(shoulder, int(theta1));
      elbow = append(elbow, int(theta2));
      x = append(x, int(xcoordinate));
      y = append(y, int(ycoordinate));
  }

}

/* mouseDragged() keeps track of the mouse
   coordinates while being dragged and sends
   them over serial*/
void mouseDragged() {
  stroke(255);
  ellipse(mouseX,mouseY,5,5);
  if(inbounds(mouseX, mouseY)) {
      mapCoordinates(mouseX, mouseY); //get adjusted coordinates
      getAngles(xcoordinate, ycoordinate); //change coordinates to angles
      sendAngles(); //send them over serial
      shoulder = append(shoulder, int(theta1));
      elbow = append(elbow, int(theta2));
      x = append(x, int(xcoordinate));
      y = append(y, int(ycoordinate));
  }
}

/* sendAngles() sends two ints over serial in
   the form 2,3'\n' for the arudino to parse*/
void sendAngles() {
    int angle1 = touSec(theta1);
    int angle2 = touSec(theta2);
    xyline = angle1 + "," + angle2 + "\n";
    String lol = int(xcoordinate) + "," + int(ycoordinate);
    print("Sent: " + lol + ',' + xyline);
    port.write(xyline);
}

//Given target(Px, Py) solve for theta1, theta2 (inverse kinematics)
void getAngles(float Px, float Py) {
  // first find theta2 where c2 = cos(theta2) and s2 = sin(theta2)
  c2 = (pow(Px,2) + pow(Py,2) - pow(l1,2) - pow(l2,2))/(2*l1*l2); //is btwn -1 and 1
  //if (elbowup == false) {  # for now, commented out because assume always elbowdown solution
  s2 = sqrt(1 - pow(c2,2));  //sqrt can be + or -, and each corresponds to a different orientation
  theta2 = degrees(atan2(s2,c2));  // solves for the angle in degrees and places in correct quadrant
  theta1 = degrees(atan2(-l2*s2*Px + (l1 +  l2*c2)*Py,
                         (l1 + l2*c2)*Px + l2*s2*Py));

}

/* inbounds() checks to see if the mouse position
   is actually on the drawing window */
boolean inbounds(int x, int y) {
    if(x > 0 && y > 0 && x < width && y < height){
        return true;
    } else {
        return false;
    }
}

/* mapCoordinates() takes the x and y cooridantes
   from the mouse and changes them to numbers
   suitable for the arduino to control the servos*/
void mapCoordinates(float x, float y) {
    xcoordinate = -1*(x/width)*50;
    ycoordinate = -1*(y/height)*50+90;
}
   


void keyPressed() { // Press a key to save the data
    String[] lines = new String[x.length];
    for (int i = 0; i < x.length; i++) {
        lines[i] = int(touSec(shoulder[i])) + "," + int(touSec(elbow[i])) + "," + x[i] + "," + y[i];
    }
    saveStrings("/home/cappie/sketchbook/lines.txt", lines);
    exit(); // Stop the program
}

int touSec(float angle) {
    return int((angle/180)*1900 + 500);
}