Cursor c;
void setup()
{
  size(500,200);
  noCursor();
  c = new Cursor(loadImage("cursor.png"));
}

void draw()
{
  if(!mousePressed) background(0);
  c.update(10);
  c.draw();
}

class Cursor
{
  PImage img;
  int px, py, x, y;
  float theta,ttheta;
  Cursor(PImage _img)
  {
    img = _img;
    update(1);
  }

  void update(int C)
  {
    if(!(pmouseX==mouseX && pmouseY==mouseY)){
	px = pmouseX;
	py = pmouseY;
	x = mouseX;
	y = mouseY;
	ttheta = angle(x,y,px,py)-HALF_PI;
    }
    theta += (ttheta-theta)/C;
  }

  void draw()
  {
    stroke(255);
    fill(220);
    pushMatrix();
    translate(x,y);
    rotate(theta);
    image(img,0,0);
    popMatrix();
  }
}

float angle(float x, float y, float px, float py)
{
  float dx = px-x;
  float dy = py-y;
  float r  = atan2(dy,dx);
  return r;
}