How to draw to a gameloop

Newbie & Debugging Questions
#1

I am reading killer game programming in java and reffering to foriegnguymike on youtube. I think my game loop is ok but someone said not to use thread.sleep() and i’ll work on it. For now based on that youtuber I’m trying to draw the player using its’ methods. Anything unprofessional please point out because I’m new to advanced game programming with loops. I’ll show you my classes and PLEASE criticize by explaining what I did wrong, what I can correct and how I can draw an image from a resource folder. I really need to understand how to draw images in this gameloop

Main CLass


    import javax.swing.JFrame;

     public class Game {
  
     public static void main(String[] args) {
        JFrame f = new JFrame();
        f.setTitle("OMG I MADE A GAME");
        f.setResizable(true);
        f.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        f.setContentPane(new Panel());
        f.pack();
         
        f.setVisible(true);
     }
  
          }

JPanel Class



      import java.awt.*;
      import java.awt.image.BufferedImage;
      import java.awt.event.*;
    
      import javax.swing.JPanel;
    
      import com.game.entity.Player;
    
    
    
   
     public class Panel extends JPanel 
      implements Runnable, KeyListener{
     
      //game objects
     private Player p;///////////new Player
     
     // dimensions
     public static final int WIDTH = 320;
     public static final int HEIGHT = 240;
     public static final int SCALE = 2;
   
     // game thread
     private Thread thread;
     private boolean running;
    
     // image
     private BufferedImage image;
     private Graphics2D g;
     
     public Panel() {
        super();
        setPreferredSize(new Dimension(WIDTH * SCALE, HEIGHT * SCALE));
        setFocusable(true);
        requestFocus();
     }
     // DRAWS PANEL TO FRAME
     public void addNotify() {
        super.addNotify();
        if(thread == null) {
           thread = new Thread(this);
           addKeyListener(this);
           thread.start();
        }
     }
     
     private void init() {
        
        image = new BufferedImage(
                 WIDTH, HEIGHT,
                 BufferedImage.TYPE_INT_RGB
              );
        g = (Graphics2D) image.getGraphics();
        
        running = true;
        p.init();
        p = new Player(100, 100);
     }
     
     public void run() {
        
        init();
        
        // game loop
        while(running) {
           
           update();
           draw();
           p.draw(g);
           drawToScreen();         
           
           try  {
              Thread.sleep(10);
           }
           catch(Exception e) {
              e.printStackTrace();
           }
           
        }
       
      }
     
      private void update() {
        p.update();
     }
     private void draw() {
        p.draw(g);
     }
     private void drawToScreen() {
        Graphics g2 = getGraphics();
        g2.drawImage(image, 0, 0,
              WIDTH * SCALE, HEIGHT * SCALE,null);
        
        g.drawString("2014 Jay H.", 10, 230);
        g2.dispose();
     }
     
     public void keyTyped(KeyEvent key) {}
    
     // PUBLIC KEYRELEASES
     public void keyPressed(KeyEvent key) {
        
     } 
     // PUBLIC KEYRELEASES
     public void keyReleased(KeyEvent key) {
  
     }
  
      }

Player Class


      import java.awt.Graphics2D;
       import java.awt.Image;
  
     import javax.swing.ImageIcon;
  
     public class Player {
     
       // PLAYER CORDINATES AND VELOCITY
       int x,y,dx,dy;
     
     
       //   PLAYER IMAGE
     private Image PImg; 
     
     public Player(int x, int y) {
              
     }
     
     public void init() {//////////////////////////// How to get image from resource folder
        //GET IMAGE OF PLAYER IN THE SAME PACKAGE
        ImageIcon i = new ImageIcon(this.getClass().getResource("playersprites.gif"));
        PImg = i.getImage();
     }
   
     public void update() {
        this.x += dx;
        this.y += dy;
     }
     
     // DRAW TO PANEL CLASS
     public void draw(Graphics2D g) {
        g.drawImage(PImg, x, y, null);
      } 
     
      //GET METHODS FOR CORDINATES AND VELOCITY  (Unused for now... i think)
     public void getX() {}
     public void getY() {}
     public void getDX() {}
      public void getDY() {}
  
         }

Also point me out to some good game loop tutorials that explains how to add graphics

#2

You asked for criticism, so I’ll give it to you. :wink:

 public void run() {
        
        init();
        
        // game loop
        while(running) {
           
           update();
           draw();
           p.draw(g);
           drawToScreen();         
           
           try  {
              Thread.sleep(10);
           }
           catch(Exception e) {
              e.printStackTrace();
           }
           
        }
       
      }
     private void draw() {
        p.draw(g);
     }

Here, you’re drawing the player twice: once in the draw method, then in the game loop. Remove the one in the loop. Drawing should be done in the draw method. Same thing with drawToScreen(). Don’t call that directly from the game loop; instead, call it from the draw method.

Who told you not to use Thread.sleep()? That is the only way that I have ever seen it done. I think you’re only other option would be to run intensive calculations on the cpu until enough time has passed, but that would be HORRIBLE. Using Thread.sleep() is fine.

The rest of the code looks good, nothing else worth noting. My advice is to just keep learning :smiley:

Edit: You don’t have to keep creating new topics. There’s an edit button in the top right of your post.

#3

There is also the possibility of using a util Timer for game loops. In Killer Game Programming, the author demonstrates both short-comings of the Swing Timer and the excellent accuracy of the util Timer. However, the author has a strong preference for methods that make use of a variable amount of Sleep rather than using a Timer, and most Java game programmers (at least around here) follow this practice.

#4

Oh yes, I completely forgot about timer (probably because I never use it :D)

#5

Some tips:

  • your code formatting makes my brain hurt. Use a consitent code formatting style so others can read your code.
    Eclipse has an autoformat function (alt+shift+f I think) that can help with this.
  • for a good game loop see this article to get a clear grasp.