Processingのキャンバス上で手書きで座標値を取得し、速度ベクトルを描画する

import controlP5.*;

ControlP5 cp5;

IntList xarr;
IntList yarr;
IntList vxArr;
IntList vyArr;
int cnt=0;
boolean isFinished = false;
int cursor = 0;
boolean drawVelocityEnabled = false;

void setup() {
  size(800, 400);
  cp5 = new ControlP5(this);
  setupButton(cp5);
  background(255);
  xarr = new IntList();
  yarr = new IntList();
  rect(50, 50, 300, 300);
}

void setupButton(ControlP5 cp5) {
  cp5.addButton("Finish")
    .setPosition(10, 10)
    .setSize(100, 19)
    ;
  cp5.addButton("Calculate")
    .setPosition(150, 10)
    .setSize(100, 19)
    ;
  cp5.addButton("Reset")
    .setPosition(300, 10)
    .setSize(100, 19)
    ;
}

public void Finish() {
  isFinished = true;
  int xLastIdx = xarr.size()-1;
  int xLastElem = xarr.get(xLastIdx);
  int xLastLastElem = xarr.get(xLastIdx-1);
  int yLastIdx = yarr.size()-1;
  int yLastElem = yarr.get(yLastIdx);
  int yLastLastElem = yarr.get(yLastIdx-1);

  xarr.remove(xLastIdx);
  yarr.remove(yLastIdx);
  while (true) {
    if (xLastElem==xLastLastElem && yLastElem==yLastLastElem) {
      xLastIdx = xLastIdx-1;
      yLastIdx = yLastIdx-1;
      xarr.remove(xLastIdx);
      yarr.remove(yLastIdx);
      xLastElem = xLastLastElem;
      xLastLastElem = xarr.get(xLastIdx-1);
      yLastElem = yLastLastElem;
      yLastLastElem = yarr.get(yLastIdx-1);
    } else {
      break;
    }
  }

  plot();
}

public void Calculate() {
  int vx;
  int vy;
  vxArr = new IntList();
  vyArr = new IntList();
  for (int i=0; i<xarr.size()-2; i++) {
    vx = xarr.get(i+1)-xarr.get(i);
    vy = yarr.get(i+1)-yarr.get(i);
    vxArr.append(vx);
    vyArr.append(vy);
  }
  drawVelocityEnabled = true;
}

public void Reset(){
  xarr = new IntList();
  yarr = new IntList();
  vxArr = new IntList();
  vyArr = new IntList();  
  isFinished = false;
  cursor = 0;
  plot();
}

void drawArrow(int cx, int cy, int len, float angle) {
  plot();
  pushMatrix();
  translate(cx, cy);
  rotate(radians(angle));
  line(0, 0, len, 0);
  line(len, 0, len - 8, -8);
  line(len, 0, len - 8, 8);
  popMatrix();
}

int rad = 0;
void draw() {
  if (!isFinished && mousePressed) {
    xarr.append(mouseX);
    yarr.append(mouseY);
    plot();
  }
  if (drawVelocityEnabled) {
    drawVelocityArrow();
  }
}

void drawVelocityArrow() { 
  int cx = 600;
  int cy = 200;
  int vx = vxArr.get(cursor);
  int vy = vyArr.get(cursor);
  int len = int(sqrt(vx*vx+vy*vy));
  float angle = degrees(atan2(vy, vx));
  print("vector: ");
  print(len);
  print(", ");
  println(angle);
  drawArrow(cx, cy, len*5, angle);  
  if (cursor==vxArr.size()-1) {
    drawVelocityEnabled = false;
  } else {
    cursor++;
  }
  delay(10);
}

void plot() {
  background(255);
  rect(50, 50, 300, 300);
  for (int i=0; i<xarr.size()-1; i++) {
    point(xarr.get(i), yarr.get(i));
    line(xarr.get(i), yarr.get(i),
      xarr.get(i+1), yarr.get(i+1));
  }
}

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