int a = 1000;
float cx, cy;
float bx, by;
boolean grabbed = false;

void setup(){
  size(400, 400);
  bx = random(width);
  by = random(height);
}

void draw(){
  background(255); // don't forget to clear at each frame
  
  noFill();
  if(a < width){
    ellipse(cx, cy, a, a);
    a = a + 10;
  }
  
  fill(0);
  ellipse(bx, by, 30, 30);

  if(mousePressed){
    fill(0);
  }
  else{
    noFill();
  }
  line(mouseX, mouseY, pmouseX, pmouseY);
  ellipse(mouseX, mouseY, 10, 10);
}

void mouseDragged(){
  if(grabbed){
    bx = mouseX;
    by = mouseY;
  }
}

void mousePressed(){
  if(dist(mouseX, mouseY, bx, by) < 30){
    grabbed = true;
  }
}

void mouseReleased(){
  grabbed = false;
}

void mouseClicked(){
  a = 10;
  cx = mouseX;
  cy = mouseY;
}