How do you get a line to shoot in random directions with drawLine()?

Question

I'm working on a fun assignment that consists of a little ship that moves with the mouseMoved() and shoots laser beam in random directions. I want to use drawLine(mouse_x, mouse_y, ?, ?)for the laser but I can't define the coordinates of x2 and y2. The laser has to cross the screen.

This is what I have so far. page.drawLine(mouse_x-15, mouse_y-5,300,300);of course I don't want the laser to keep shooting at the corner (300,300).

import java.applet.*;
import java.awt.*;
import java.awt.event.*;


public class SpaceShip extends Applet
   implements MouseListener, MouseMotionListener {

   private int applet_width = 300; //width of applet
   private int applet_height =300; //height of applet
   private int mouse_x, mouse_y;  // the mouse coordinates
   private int shots = 0; //count of shots
   private boolean buttonPressed = false;


   //init()
   public void init() {
      setSize(applet_width, applet_height); //set size of applet
      setBackground( Color.black ); //set color of background

      mouse_x = applet_width/2; //initiate mouse in the middle of the applet
      mouse_y = applet_height/2;

      addMouseListener( this ); //adding mouse listener
      addMouseMotionListener( this ); // adding motion listener
   }


  // Drawing of the spaceship and laser beam
   public void paint( Graphics page ) {

          page.setColor(colorRand()); // random color laser beam
          page.drawLine(mouse_x-15, mouse_y-5,300,300);

          page.setColor( Color.YELLOW );//yellow spaceship
          page.fillOval( mouse_x-30, mouse_y-15, 60, 30 );


       }

   public void mouseEntered( MouseEvent e ) {

   }
   public void mouseExited( MouseEvent e ) {

   }
   public void mouseClicked( MouseEvent e ) {
      shots++;
      showStatus("Number of shots: " + shots);

   }
   public void mousePressed( MouseEvent e ) { 
      buttonPressed = true;  
      repaint();

   }
   public void mouseReleased( MouseEvent e ) {
      buttonPressed = false;
      setBackground( Color.black );
      repaint();

   }
   public void mouseMoved( MouseEvent e ) { 
      mouse_x = e.getX();
      mouse_y = e.getY();
      repaint();

   }
   public void mouseDragged( MouseEvent e ) {

   }

   //method generating a random color RGB
   public Color colorRand(){

       int r = (int)(Math.random()*256);
       int g = (int)(Math.random()*256);
       int b = (int)(Math.random()*256);

        Color randomColor = new Color(r,g,b);
        return randomColor;
   }


}

Thank you in advance, I've been stuck on this for quite a while now.

Didi

why not use Math.random() to get the laser to shoot somewhere random? — Outsider, Apr 13 '14 at 05:33

score 3 · Answer 1 · edited May 23 '17 at 12:05

3

You could use a small algorithm :

//find a random angle :
double randomAngle = Math.random()*Math.PI*2;

//find the diameter of the circle around your ship that contains all the screen
int maxX = Math.max( mouse_x, screenWidth - mouse_x );
int maxY = Math.max( mouse_y, screenHeight - mouse_y );
int diam = (int) Math.sqrt( maxX * maxX + maxY * maxY );

//Then take the point of this circle at randomAngle : 
int x2 = mouse_x + (int) diam*Math.cos( randomAngle );
int y2 = mouse_y + (int) diam*Math.sin( randomAngle );
page.drawLine( mouse_x - 15, mouse_y - 5, x2, y2 );

Where you could get the screen dimensions, like in this thread : How can I get screen resolution in java?.

edited May 23 '17 at 12:05

Community

1
1

answered Apr 13 '14 at 05:33

Snicolas

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I actually tried that but the line has to continue across the screen. – Didi Bui Apr 13 '14 at 05:46
What do you mean ? All Screen ? Or from your ship to a border of the screen ? – Snicolas Apr 13 '14 at 05:47
Correct from the ship to the border of the screen – Didi Bui Apr 13 '14 at 05:49
Yitzih and Snicolas, I'm impressed. You guys kick ass. – Didi Bui Apr 13 '14 at 06:00
No secret, practice a lot. – Snicolas Apr 13 '14 at 06:04

score 3 · Accepted Answer · answered Apr 13 '14 at 05:48

How do you get a line to shoot in random directions with drawLine()?

2 Answers2