// A class which defines a pupil and the constraints within which it can move.

import java.awt.*;

public class Pupil
{
	private int pupil_size, pupil_x, pupil_y;
	private int center_x, center_y;
	private int radius, right_border, left_border;
	
	public Pupil (int r, int cx, int cy, int rb, int lb, int ps)
	{
		radius = r;
		pupil_x = center_x = cx;
		pupil_y = center_y = cy;
		right_border = rb;
		left_border = lb;
		pupil_size = ps;
	}
	
	// Update where the eye is looking.
	public void update (int stare_x, int stare_y)
	{
		float height = center_y - stare_y;
		float width = center_x - stare_x;
		
		// Calculate the position of the pupil within the radius of the eye.
		float hypot = (float)Math.sqrt(height * height + width * width);
		pupil_x = (int)(center_x - (radius / hypot) * width);
		pupil_y = (int)(center_y - (radius / hypot) * height);
		
		// Adjust the eye if it is outside the left or right borders.
		if (pupil_x < right_border)
			pupil_x = right_border;
		else if (pupil_x > left_border)
			pupil_x = left_border;
	}
	
	// Draw the pupil.
	public void draw (Graphics g)
	{
		// White background for eyeball.
		g.setColor(Color.WHITE);
		g.fillRect(center_x - radius*2, center_y - radius*2, radius*4, radius*4);
		// Draw the pupil.
		g.setColor(Color.BLACK);
		g.fillOval(pupil_x - pupil_size / 2, pupil_y - pupil_size / 2, pupil_size, pupil_size);
	}
}