CODEWITHSUNDEEP
javagame-physics
user2309865
user2309865

Reputation: 377

Basic 2D path finding (no graph needed)

I am working on a game (just for my own fun) in Processing (a variant of Java), and have run into a problem. I have a projectile class that is created and managed by a Castle class, and it goes towards an Enemy class (which is a moving target). What I am trying to do (conceptually) is make this projectile find its intended target (Euclidian distance), say its 20 units away, and move 5 units along that line (i.e. 1/4 of the way there). My problem is that I don't know how to extract the x and y components of that vector to update this projectile's position. Here is my projectile class currently:

class Projectile{

  private PImage sprite;
  private Enemy target;
  private int x;
  private int y;
  private int speed;

  public Projectile(PImage s, Enemy t, int startx, int starty, int sp) throws NullPointerException{
    if(t == null){
      if(debug){
        println("Null target given to Projectile(), throwing exception");
      }
      throw new java.lang.NullPointerException("The target of the projectile is null");
    }
    sprite = s;
    target = t;
    x = startx;
    y = starty;
    speed = sp;
    if(debug){
      println("Projectile created: " + t + " starting at position: " + startx + " " + starty);
    }
  }


  public void update(){
    if(target != null){
      int goingToX = target.getCenterX() ;
      int goingToY = target.getCenterY();

      //find the total distance to the target
      float d = dist(this.x, this.y, target.getCenterX(), target.getCenterY());
      //divide it by the velocity vector
      d /= speed;

      //get the dx and dy components of the vector



    }else{//target is null, i.e. already destroyed by something else
      //destroy this projectile
      //if the higher functions were correct, then nothing needs to go here
      //this should be deleted as long as it checks for this.hitTarget()
      return;
    }
  }

  public void render(){
    image(sprite, x, y, 10, 10);
  }

  //checks if it hit the target, but does a little bit of rounding because the sprite is big
  //done this way in the interest of realism
  public boolean hitTarget(){
    if(target != null){
      if(abs(x - target.getCenterX()) <= 5 && abs(y - target.getCenterY()) <= 5 ){
        return true;
      }else{
        return false;
      }
    }
    //this activates if the target is null, which marks this for deletion
    return true;
  }
}

I've been researching this for hours and realized my approach was unnecessarily complicated when I was looking into converting floats into strings, formatting them to some number of decimal places, then trying to convert that into a fraction which I would then reduce. I feel like this is far easier than I realize, but I am lacking the math background to do it. All necessary changes should only need to be done in Projectile.update(). Thanks!

Upvotes: 0

Views: 316

Answers (1)

Sinkingpoint
Sinkingpoint

Reputation: 7624

Assuming that you want your projectile to 'track' the target, then you can use a simple bit of trig to work out the relative speeds in x and y:

//Calculate the differences in position
float diffX = target.getCenterX() - this.x;
float diffY = target.getCenterY() - this.y;

//Calculate the angle
double angle = Math.atan2(diffY, diffX);

//Update the positions
x += Math.cos(angle) * speed;
y += Math.sin(angle) * speed;

This essentially calculates the angle between the projectile and the target, then moves the projectile in that direction, based on the speed given.

Upvotes: 3

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