Firing bullet from gun's current position to mouse x & y position

Java 2D
#1

Please help I’m kinda lost in my coding.

So I’ve created a bullet class:

package javagame.states;

import org.newdawn.slick.Color;
import org.newdawn.slick.GameContainer;
import org.newdawn.slick.Graphics;
import org.newdawn.slick.Image;
import org.newdawn.slick.Input;
import org.newdawn.slick.SlickException;
import org.newdawn.slick.geom.Vector2f;
import org.newdawn.slick.state.StateBasedGame;

public class Bullet {

    private Vector2f pos;
    private Vector2f speed;
    private int lived = 0;

    private boolean aktiv = true;

    private static int MAX_LIFETIME = 2000;

    public Bullet (Vector2f pos, Vector2f speed){
        this.pos = pos;
        this.speed = speed;
    }

    public Bullet(){
        aktiv = false;
    }

    public void update(int t){

        rotation++;

        if(aktiv){
            Vector2f realSpeed = speed.copy();
            realSpeed.scale((t/1000.0f));
            pos.add(realSpeed);

            lived += t;
            if(lived > MAX_LIFETIME) aktiv = false;
        }
    }

    public void init(GameContainer gc, StateBasedGame sbg) throws SlickException{
    }

    public void render(GameContainer gc, Graphics g) throws SlickException {

        if(aktiv){
            g.setColor(Color.red);
            g.fillOval(pos.getX(), pos.getY(), 10, 10);
        }
    }

    public boolean isAktiv(){
        return aktiv;
    }
}

then called the bullet class here in my robot class:

package javagame.states;

import java.util.Iterator;
import java.util.LinkedList;

import org.newdawn.slick.GameContainer;
import org.newdawn.slick.Graphics;
import org.newdawn.slick.Input;
import org.newdawn.slick.SlickException;
import org.newdawn.slick.geom.Vector2f;
import org.newdawn.slick.state.BasicGameState;
import org.newdawn.slick.state.StateBasedGame;

public class Robot2 extends BasicGameState{

    private LinkedList<Bullet> bullets;

    @Override
    public void init(GameContainer gc, StateBasedGame sbg) throws SlickException {
        bullets = new LinkedList<Bullet>();
    }

    @Override
    public void render(GameContainer gc, StateBasedGame sbg, Graphics g) throws SlickException {
        for(Bullet b : bullets){
            b.render(gc, g);
        }       
    }

    @Override
    public void update(GameContainer gc, StateBasedGame sbg, int delta) throws SlickException {
        Iterator<Bullet> i = bullets.iterator();
        while(i.hasNext()){
            Bullet b = i.next();
            if(b.isAktiv()){
                b.update(delta);
            }else{
                i.remove();
            }
        }

        Input input = gc.getInput();
        int mouseX = input.getMouseX();
        int mouseY = input.getMouseY();

        int xDistance = (int) (RobotX() + Robotwidth() / 2 - mouseX); //RobotX is the robot image x position same to RobotY
        int yDistance = (int) (RobotY() + Robotheight() / 2 - mouseY);
        double angleToTurn = Math.toDegrees(Math.atan2(yDistance, xDistance));

            if(mouseX != 0){
            angleToTurn += 270;
            }else{
            if(mouseY != 0)
            angleToTurn += 180;
            }
            robot.setRotation((float) angleToTurn); //robot is an image. didn't included the code here to shorten my codes

                if(gc.getInput().isMousePressed(Input.MOUSE_LEFT_BUTTON)){
            bullets.add(new Bullet(new Vector2f(Sprites.getRobotX(), Sprites.getRobotY()), new Vector2f(mouseX, mouseY)));
        }
    }

    @Override
    public int getID() {
        return States.ROBOT;// has an integer value
    }

}

The robot is rotating perfectly according to mouse’s cursor movement but when I hit the mouse’s left button to fire a bullet, it doesn’t follow the mouse’s cursor location. This is what I’ve got when i run these codes and pressing the left button of my mouse. Please check my sample image.

http://s12.postimg.org/kwsr41p71/Untitled_1.jpg

What I want to achieve is to correct the direction of the bullet according to mouse cursor location.

Any help would be greately much appreciated. Thank you very much.

#2

This question has been asked numerous times before, I suggest you use the search bar in the top right before you create a topic next time!
Anyways, here’s a link to a topic with a good answer. Best of luck.

http://www.java-gaming.org/topics/creating-projection-of-a-projectile-using-linear-algebra/28310/msg/256834/view.html

#3

this might help you this is my projectile class it works fine!

package com.zgr.Projectile;

import java.awt.Graphics2D;
import java.awt.Rectangle;
import java.util.Random;
import java.util.Vector;

import com.zgr.Traps.ProjectileLauncher.ProjectileType;
import com.zgr.assets.Map;
import com.zgr.assets.Vector2F;
import com.zgr.tile.Tile;

public class Projectile extends Rectangle{

	final int width = 8;
	final int height = 8;
	
	ProjectileType type;

	float timeStep=60f/60f;
	
	float turretX=0f;
	
	float turretY=0f;
	
	float bulletSpeed;
	
	float bulletX;
	float bulletY;
	
	boolean isAlive;
	/*
	 * Fix The Detection Radius For the Projectile Trap
	 * Fix 2 Networking tutorials
	 * Fix So Projectile Shoots the bullets past player if thay dont hit
	 * Fix So Projectiles Rotate!
	 */

	public Projectile(float startX, float startY, float bulletSpeed, ProjectileType type) {
		isAlive = true;
		turretX = startX;
		turretY = startY;
		bulletX=turretX;
		bulletY=turretY;
		
		Random ran = new Random();
		int random = ran.nextInt(200);
		if(random > 150){
			bulletSpeed = random;
		}
		
		dirX = (float) (Map.player.xpos + 12 + Map.xOffset - turretX);
		dirY = (float) (Map.player.ypos + Map.yOffset - turretY);
		setBounds((int) (bulletX - Map.xOffset), (int) (bulletY - Map.yOffset), width, height);
		this.bulletSpeed = bulletSpeed;
		this.type = type;
	}
	
	public void render(Graphics2D g){
		if(isAlive){
			
			switch(type){
			
				case BOX:
					g.drawRect((int) (bulletX - Map.xOffset),(int) (bulletY - Map.yOffset), width, height);
				break;
				case ROUND:
					g.drawOval((int) (bulletX - Map.xOffset),(int) (bulletY - Map.yOffset), width, height);
				break;
			}
			
		}
		
	}
	float dirX;
	float dirY;
	public void tick(double deltaTime){
		if(isAlive){
			setBounds((int) (bulletX - Map.xOffset), (int) (bulletY - Map.yOffset), width, height);
			
			float dirLength= (float) Math.sqrt(dirX*dirX + dirY*dirY);
			dirX=dirX/dirLength;
			dirY=dirY/dirLength;
			
			bulletX=bulletX+(dirX*bulletSpeed*timeStep);
			bulletY=bulletY+(dirY*bulletSpeed*timeStep);
			
		}
	}

	public void setAlive(boolean b) {
		isAlive = b;
	}
	
	public boolean isAlive() {
		return isAlive;
	}
	
}
#4

This should actually be in the Newbie & Debugging board. Now what VIrtueeL works great but if you know anything of vector math, you can get the job done a lot easier like this:


public class Bullet {

     Vector2d pos;
     Vector2d dir;

     public Bullet(int x, int y) {
          pos = new Vector2d(x, y);
          dir = new Vector2d(new Vector2d(mousex, mousey).sub(pos).normalise());
     }

     public void render() {
          // Render bullet at pos.x and pos.y
     }

     public void update() {
          pos.add(dir); // Moves position to direction aka mouse. To have the bullet follow the mouse like a homing missle you would have to constantly keep updating the dir vector
     }

}

That should do it. By the way, I used to use Java2D. I actually made a complete game out of it, however, I wouldn’t recommend it in the long term. It’s just not made for games IMO. I’m sure your mind set is if I use a library I’m cheating, right? Well I’m here to tell you, all of us on this forum use libraries. It’s not cheating, It’s just being efficient. So I recommend you go and check out these 2 great libraries:

Slick2D: (This is where I went to after leaving J2D and still use it now)
Download
Beginner Tutorials

LibGDX: (Cross-platform support and apparently super easy (I find it confusing but I’m an idiot so ::slight_smile: ))
Download
Beginner Tutorials

Good luck! Choose wisely! :wink: