int x1=85;
int y1=20;
int cx1=10;
int cy1=10;
int cx2=90;
int cy2=90;
int x2=15;
int y2=80;
boolean x1_up=false, x1_down=false, cx1_up=false,  cx1_down=false, cx2_up=false, cx2_down=false, x2_up=false, x2_down=false;

void draw() {
  background(255,255,255);
  stroke(255, 102, 0);
  line(x1,y1, cx1, cy1);
  line(cx2, cy2, x2, y2);
  ellipse(x1,y1,5,5);
  ellipse(cx1,cy1,5,5);
  ellipse(x2,y2,5,5);
  ellipse(cx2,cy2,5,5);
  stroke(0, 0, 0);
  bezier(x1,y1, cx1, cy1, cx2, cy2, x2, y2);
  noLoop();
}

void mouseReleased() {
  if (x1_up) {
    println("ignore x1");
    x1_up = false;
    x1_down = true;
  }
  if (x2_up) {
    println("ignore x2");
    x2_up = false;
    x2_down = true;
  }
  if (cx1_up) {
    println("ignore cx1");
    cx1_up = false;
    cx1_down = true;
  }
  if (cx2_up) {
    println("ignore cx2");
    cx2_up = false;
    cx2_down = true;
  }
}

void mouseDragged() {
  if (x1_up && mouseX < width && mouseX > 0 && mouseY > 0 && mouseY < height) {
    println("drag x1");
    x1 = mouseX;
    y1 = mouseY;
  }
  if (x2_up && mouseX < width && mouseX > 0 && mouseY > 0 && mouseY < height) {
    println("drag x2");
    x2 = mouseX;
    y2 = mouseY;
  }
  if (cx1_up && mouseX < width && mouseX > 0 && mouseY > 0 && mouseY < height) {
    println("drag cx1");
    cx1 = mouseX;
    cy1 = mouseY;
  }
  if (cx2_up && mouseX < width && mouseX > 0 && mouseY > 0 && mouseY < height) {
    println("drag cx2");
    cx2 = mouseX;
    cy2 = mouseY;
  }
    redraw();
}

void mousePressed() {
  // To prevent point from ending up on top of one another and then being dragged together without being able
  // to split them up again, we use 'else'. This means that x1 will always be on top, x2 next, then cx1 and 
  // then cx2.
  if ((!x1_up) && ((mouseX <= (x1 + 5) && mouseX >= (x1 - 5)) && (mouseY <= (y1 + 5) && mouseY >= (y1 - 5)))) {
    println("lift x1");
    x1_up = true;
  } else
  if ((!x2_up) && ((mouseX <= (x2 + 5) && mouseX >= (x2 - 5)) && (mouseY <= (y2 + 5) && mouseY >= (y2 - 5)))) {
    println("lift x2");
    x2_up = true;
  } else
  if ((!cx1_up) && ((mouseX <= (cx1 + 5) && mouseX >= (cx1 - 5)) && (mouseY <= (cy1 + 5) && mouseY >= (cy1 - 5)))) {
    println("lift cx1");
    cx1_up = true;
  } else
  if ((!cx2_up) && ((mouseX <= (cx2 + 5) && mouseX >= (cx2 - 5)) && (mouseY <= (cy2 + 5) && mouseY >= (cy2 - 5)))) {
    println("lift cx2");
    cx2_up = true;
  }
}