pendulum

import greenfoot.*;  // (World, Actor, GreenfootImage, Greenfoot and MouseInfo)

/**
 * Write a description of class Pendulum here.
 * 
 * @author (your name) 
 * @version (a version number or a date)
 */
public class Pendulum extends Actor
{
    
    private double angle = Math.PI / 2;
    private int length;
    
    public Pendulum(int length)
    {
        this.length = length;
        
    }
    
     /**
     * Act - do whatever the Pendulum wants to do. This method is called whenever
     * the 'Act' or 'Run' button gets pressed in the environment.
     */
    
    public void act() 
    {
        // Add your action code here.
        drawPendulum();
        run();
    }
    
    public void drawPendulum()
    {
        GreenfootImage gfim = new GreenfootImage(900,600);
        
        gfim.setColor(Color.WHITE);
        gfim.fillRect(0, 0, gfim.getWidth(), gfim.getHeight());
        gfim.setColor(Color.BLACK);
        int anchorX = gfim.getWidth() / 2, anchorY = gfim.getHeight() / 4;
        int ballX = anchorX + (int) (Math.sin(angle) * length);
        int ballY = anchorY + (int) (Math.cos(angle) * length); 
        gfim.drawLine(anchorX, anchorY, ballX, ballY);
        gfim.fillOval(anchorX - 3, anchorY - 4, 7, 7);
        gfim.fillOval(ballX - 7, ballY - 7, 14, 14);
        
        this.setImage(gfim);
    }
        
    public void run()
    {    
        double angleAccel, angleVelocity = 0, dt = 0.5;
        
            angleAccel = -9.81 / length * Math.sin(angle);
            angleVelocity += angleAccel * dt;
            angle += angleVelocity * dt;
            
            
        
    
    }
}