Back to For Beginners

[Java] Draw something more than once?

For Beginners

Started by LeisureForce October 04, 2012 03:47 AM

13 comments, last by rockstar8577 11 years, 6 months ago

LeisureForce

119

Author

October 04, 2012 03:47 AM

Hey all, I'm a beginner to the LWJGL framework, and cannot for the life of me figure this out. I am recreating the space invader game. I have the ship on the screen and moving, but I can't draw the bullet so that you can have more than 1 on the screen. Right now it just draws and goes forward when you push space, but stops drawing when you let go of space. And then when you hit space again, it draws from where it left off. Here is the code



import static org.lwjgl.opengl.GL11.*;

import java.io.File;

import java.io.FileInputStream;

import java.io.FileNotFoundException;

import java.io.IOException;

import java.util.ArrayList;

import java.util.List;

import java.util.Random;

import org.lwjgl.input.Mouse;

import org.lwjgl.input.Keyboard;

import org.lwjgl.opengl.*;

import org.lwjgl.*;

import org.newdawn.slick.opengl.Texture;

import org.newdawn.slick.opengl.TextureLoader;

import org.newdawn.slick.util.ResourceLoader;

public class Move {

private static Texture texture;



private static Texture bull;



public static int mx = 200;



public static int my = 400;



public static int bvelx = SetShip.x;



public static int bvely = SetShip.y;



public static void main(String[] args){



  setUpDisplay(640,480);

  SetShip.init();

  ShootBullet.init();



  while (true){

   glClear(GL_COLOR_BUFFER_BIT);

   SetShip.draw();

   logic();



   Display.update();

   Display.sync(60);



   if(Display.isCloseRequested()){

    Display.destroy();

    System.exit(0);

   }

  }

}

private static void logic() {

  // TODO Auto-generated method stub



  if (Keyboard.isKeyDown(Keyboard.KEY_LEFT)){

   mx = -5;

   SetShip.update(mx);

  }

  if (Keyboard.isKeyDown(Keyboard.KEY_RIGHT)){

   mx = 5;

   SetShip.update(mx);

  }

  if (Keyboard.isKeyDown(Keyboard.KEY_SPACE)){

   bvely = -15;

   ShootBullet.update(bvely);

   ShootBullet.draw();

  }



}



private static void setUpDisplay(int width, int height) {

  // TODO Auto-generated method stub

  try{

   Display.setDisplayMode(new DisplayMode(width, height));

   Display.setTitle("Space Invaders");

   Display.create();

  } catch (LWJGLException e){

   e.printStackTrace();

  }



  glEnable(GL_BLEND);

  glBlendFunc(GL_SRC_ALPHA, GL_ONE_MINUS_SRC_ALPHA);



  glMatrixMode(GL_PROJECTION);

  glLoadIdentity();

  glOrtho(0, 640, 480, 0, 1, -1);

  glMatrixMode(GL_MODELVIEW);

  glEnable(GL_TEXTURE_2D);



}



private static class ShootBullet {

  private static int bulletx = SetShip.x, bullety = SetShip.y;



  static void init(){

   try{

    bull = TextureLoader.getTexture("PNG", new FileInputStream(new File("img/bullet.png")));

   } catch (IOException e){

    e.printStackTrace();

   }

  }



  static void update(int by){

   bullety += by;

  }



  static void draw(){

   bull.bind();



   glBegin(GL_QUADS);

    glTexCoord2f(0,0);

    glVertex2f(bulletx, bullety);

    glTexCoord2f(1,0);

    glVertex2f(bulletx +50, bullety);

    glTexCoord2f(1,1);

    glVertex2f(bulletx +50, bullety+50);

    glTexCoord2f(0,1);

    glVertex2f(bulletx, bullety + 50);

   glEnd();

  }



}



private static class SetShip{



  public static int x = 200, y = 400;



  static void init() {

   // TODO Auto-generated method stub

   try{

    texture = TextureLoader.getTexture("PNG", new FileInputStream(new File("img/spaceship.png")));

   } catch (IOException e){

    e.printStackTrace();

   }



  }



  static void update(int mx){

   x += mx;

  }



  static void draw() {

   // TODO Auto-generated method stub

   texture.bind();







   glBegin(GL_QUADS);

    glTexCoord2f(0,0);

    glVertex2f(x, y);

    glTexCoord2f(1,0);

    glVertex2f(x +200, y);

    glTexCoord2f(1,1);

    glVertex2f(x +200, y+100);

    glTexCoord2f(0,1);

    glVertex2f(x, y + 100);

   glEnd();



  }

}

}

And the images used

(ship)
http://i.imgur.com/5ZsbS.png

(bullet)
http://i.imgur.com/w5qIM.png

Thanks in advance!

rockstar8577

259

October 04, 2012 04:46 AM

It's because you only have it set to update when space is held. From my knowledge you would want to have a state for the bullet being checked to see if it's still alive. If it's still alive update its position, if not remove it. I think that's right.

Viromancer

102

October 04, 2012 05:18 AM

There's a couple issues here. If your bullet is its own class, with its own update method, you need to call that method every tick on every bullet, not just when the space bar key is pressed. One way to achieve this would be to maintain an array of all bullets currently created. Then iterate through that array and call each bullet's update method every tick. This also means you should set the velocity as a property of the bullet object.

SimonForsman

7,644

October 04, 2012 06:18 AM

a few pointers to get you on the right track:

1) You are abusing static. (The only thing in your code that should be static is main, the rest shouldn't be static imo) (You don't have a bullet object, just a single global bulletx,bullety variable pair)
a static class can not be instantiated and its public members are effectivly globals. (Make a non static bullet class, create an array of bullets(in main) and add a new bullet to that array when you fire, update and draw all bullets in that array in the normal game loop.

2) You shouldn't load the image file when you shoot the bullet (loading images is slow so load them before the game starts)

[size="1"]I don't suffer from insanity, I'm enjoying every minute of it.
The voices in my head may not be real, but they have some good ideas!

DoniRamirezSoto

383

October 04, 2012 09:31 AM

I've taken a look at your code and seems that it needs bit reorganizing. Games have a main loop that consist of few functions like input (could be user or/and network), logic, and draw.Each of them should handle specifically what it says. Meaning that in the input function you would only do things that have to do with input, logic would only handle the logic that needs to be run each frame and draw should only be drawing the game object on to your canvas.

What you have done is putting the draw function of the bullet inside your (logic/input) function which not the way to go. Move the draw function of the bullet to where you draw the ship. I suppose you did this with the idea that the bullet would only be displayed when you would press a key.

My advice to you is try to improve your OO by moving the ship and the bullet to a separate class file and like SimonForsman said don't use static you have noneed for this at this point.

LeisureForce

119

Author

October 04, 2012 01:50 PM

and like SimonForsman said don't use static you have noneed for this at this point.

Thanks for your help! And I only used static because eclipse was yelling at me, and it wouldn't work unless I put a static behind everything

SimonForsman

7,644

October 04, 2012 03:33 PM

[quote name='DARSC0D3' timestamp='1349343094' post='4986701']
and like SimonForsman said don't use static you have noneed for this at this point.

Thanks for your help! And I only used static because eclipse was yelling at me, and it wouldn't work unless I put a static behind everything
[/quote]

Thats usually because you didn't instantiate the class before trying to use it.

If you have a non static class named Bullet you use it by doing:

Bullet myBullet = new Bullet(ship.x,ship.y,ship.direction); //create a new bullet instance at the ships position heading in the direction the ship is facing.

you can create as many bullets as you want this way and each bullet will get its own instance of the member variables you've defined in the Bullet class, you can also store the bullets in a Vector or List instead of a variable(which helps if you want lots of them). ( Vector<Bullet> bullets = new Vector<Bullet>();
bullets.push_back(new Bullet(ship.x,ship.y,ship.direction); //create a bullet and add it to the bullets vector.

myBullet.update(); //update the bullet instance we just created //this method should move the bullet.
myBullet.draw(); //draw the bullet we just created (normally you don't want the bullet to render itself but in this case its a bit overkill to create a proper renderer)
or if you use a vector:
for (Bullet b : bullets) {
b.update();
b.draw();
} //updates and draws all bullets
Just remove the bullets from the vector when you want to destroy them, with vectors its fastest to remove from the back, with Lists it doesn't really matter that much. (You can swap the bullet you want to remove with the last bullet in the vector before removing to speed things up if necessary)

static classes are not objects, they're effectivly just a collection of global functions and variables, (in languages such as C++ you use namespaces for this instead) and in Java they are only really useful to group support functions in a logical way.

[size="1"]I don't suffer from insanity, I'm enjoying every minute of it.
The voices in my head may not be real, but they have some good ideas!

LeisureForce

119

Author

October 04, 2012 09:31 PM

Thanks a ton!

LeisureForce

119

Author

October 04, 2012 11:50 PM

Okay, now i've taken all of that into consideration, but I still have a few problems. Now, when I go to draw the bullet, it just turns the ship purple instead of drawing a rectangle to the screen. Here is my code. (I know that i am still drawing the rectangle only when i hit space, I'm just doing it for now).

import static org.lwjgl.opengl.GL11.*;

import java.io.File;

import java.io.FileInputStream;

import java.io.FileNotFoundException;

import java.io.IOException;

import java.util.ArrayList;

import java.util.List;

import java.util.Random;

import org.lwjgl.input.Mouse;

import org.lwjgl.input.Keyboard;

import org.lwjgl.opengl.*;

import org.lwjgl.*;

import org.newdawn.slick.opengl.Texture;

import org.newdawn.slick.opengl.TextureLoader;

import org.newdawn.slick.util.ResourceLoader;

public class Move {

//make the screen width and height values public

public int SCREENWIDTH = 640, SCREENHEIGHT = 480;

private boolean isRunning = true;

private Texture spaceShip;

public int inx = 100;

public SetShip myShip = new SetShip();

public Bullet myBullet = new Bullet();

public int x = myShip.ShipXStart;

public int y = myShip.ShipYStart;



public Move(){

  //Set up the display

  try{

   Display.setDisplayMode(new DisplayMode(SCREENWIDTH, SCREENHEIGHT));

   Display.setTitle("Space Invaders");

   Display.create();

  } catch (LWJGLException e){

   e.printStackTrace();

  }











  glEnable(GL_BLEND);

  glBlendFunc(GL_SRC_ALPHA, GL_ONE_MINUS_SRC_ALPHA);



  glMatrixMode(GL_PROJECTION);

  glLoadIdentity();

  glOrtho(0, 640, 480, 0, 1, -1);

  glMatrixMode(GL_MODELVIEW);

  glEnable(GL_TEXTURE_2D);



  myShip.init();



  //main game loop

  while (isRunning){

   glClear(GL_COLOR_BUFFER_BIT);

   myShip.draw();

   input();





   Display.update();

   Display.sync(60);



   if(Display.isCloseRequested()){

    isRunning = false;

    Display.destroy();

    System.exit(0);

   }

  }

  Display.destroy();





}



private void input() {

  // TODO Auto-generated method stub

  if (Keyboard.isKeyDown(Keyboard.KEY_LEFT)){

   inx = -5;

   myShip.update(inx);

  }

  if (Keyboard.isKeyDown(Keyboard.KEY_RIGHT)){

   inx = 5;

   myShip.update(inx);

  }

  if (Keyboard.isKeyDown(Keyboard.KEY_SPACE)){

   myBullet.update(10, 20);

   myBullet.draw();

  }

}

private Texture loadTexture(String key) {

  // TODO Auto-generated method stub

  try{

   return TextureLoader.getTexture("PNG", new FileInputStream(new File("img/" + key + ".png")));

  } catch (FileNotFoundException e){

   e.printStackTrace();

  } catch (IOException e){

   e.printStackTrace();

  }

  return null;

}



public class SetShip{

  public int ShipXStart = 100, ShipYStart = 400;

  //initialize the ship

  void init(){

   //store the image in a texture

   //load the image

   try {



    spaceShip = TextureLoader.getTexture("PNG", new FileInputStream(new File("img/spaceship.png")));

   } catch (FileNotFoundException e){

    e.printStackTrace();

   } catch (IOException e){

    e.printStackTrace();

   }







  }





  void update(int inx){

   ShipXStart += inx;

  }



  void draw(){





   spaceShip.bind();



   glBegin(GL_QUADS);

    glTexCoord2f(0, 0);

    glVertex2f(ShipXStart, ShipYStart);

    glTexCoord2f(1, 0);

    glVertex2f(ShipXStart + 200, ShipYStart);

    glTexCoord2f(1, 1);

    glVertex2f(ShipXStart + 200, ShipYStart + 100);

    glTexCoord2f(0, 1);

    glVertex2f(ShipXStart, ShipYStart + 100);

   glEnd();

  }





}

private static class Bullet{

  //set up the variables

  public int x, y; //set the starting x and y for the bullets



  void update(int dx, int dy){

   x += dx;

   y += dy;

  }



  void draw(){

   glColor3f(1.0f,0f,1.0f);

   glBegin(GL_QUADS);

    glVertex2i(50, 50);

    glVertex2i(100, 100);

    glVertex2i(50, 100);

    glVertex2i(100, 100);

   glEnd();

  }



}



public static void main(String[] args) {

  // TODO Auto-generated method stub

  new Move();

}



}