Slick2d | Shooting with same speed

Question

The problem:

I succesfully implemented a shooting mechanism into my little game, but there is a problem.
The speed of the bullets are faster if my cursor is further from the player, and slower if the cursor is closer to the player.

So my question is: How can I make the bullets always go with the same speed?

Links:

The game (finished)

The code (from Shot.java):

public Shot(World world, Camera camera, float x, float y, int width, int height, Color color, float targetX, float targetY) {
    super(world, camera, x, y, width, height, color);

    this.targetX = targetX;
    this.targetY = targetY;

    dx = targetX - x;
    dy = targetY - y;
}

@Override
public void render(GameContainer gc, Graphics g) {
    g.setColor(color);
    g.fillOval(x - camera.getX(), y - camera.getY(), width, height);
}

@Override
public void update(GameContainer gc, int delta) {
    x += dx * delta * .005f;
    y += dy * delta * .005f;
}

I did it! Here is my solution (Thanks to Axis for help):

float dx, dy;
Vector2f vector;

public Shot(World world, Camera camera, float x, float y, float targetX, float targetY, int width, int height, Color color) {
    super(world, camera, x, y, width, height, color);

    dx = targetX - x;
    dy = targetY - y;

    vector = new Vector2f(dx, dy).normalise();
}

@Override
public void render(GameContainer gc, Graphics g) {
    g.setColor(color);
    g.fillOval(x - camera.getX(), y - camera.getY(), width, height);
}

@Override
public void update(GameContainer gc, int delta) {
    x += vector.getX() * delta * 0.8f;
    y += vector.getY() * delta * 0.8f;
}

score 1 · Answer 1 · answered Apr 13 '13 at 16:37

1

Your problem is here:

public Shot(World world, Camera camera, float x, float y, int width, int height, Color color, float             targetX, float targetY) {
    super(world, camera, x, y, width, height, color);
    this.targetX = targetX;
    this.targetY = targetY;

    dx = targetX - x;
    dy = targetY - y;
}

Your bullets speed is dependent on the distance from the target. Make it a constant value.

answered Apr 13 '13 at 16:37

phcoding

608
4
16

But if i set it something like dx = 100 and dy = 100, then it will always add 100 to the x and y. And becouse of this, the bullet will contantly go to one direction. (actually to the bottom right) – HUNeater Apr 13 '13 at 16:40
1

@HUNeater just normalize the vector – Axis Apr 13 '13 at 16:42
Yes so if you make dx = -100 it will go to the left :) – phcoding Apr 13 '13 at 16:45
1

You can use `if (target > x) dx = 1; if (target < x) dx = -1;` – phcoding Apr 13 '13 at 16:46
@phcoding And what about the dy? It seems different – HUNeater Apr 13 '13 at 16:53

score 1 · Accepted Answer · answered Apr 13 '13 at 16:56

1

First I would suggest switching to a vector class instead of splitting everything up into x and y. It will save you a lot of time in the long run.

All you need to do is change

public Shot(World world, Camera camera, Vector2 pos, int width, int height, Color color, Vector2 target) {
    super(world, camera, pos, width, height, color);
    this.target = target

    //dx = targetX - x; get rid of this
    //dy = targetY - y; and this

//add a vector called direction

this.direction = (target - pos).Normalize();
}

@Override
public void update(GameContainer gc, int delta) {

pos += direction * delta * bulletSpeed;
}

answered Apr 13 '13 at 16:56

Axis

826
7
22

Well, I have got some problems... The Slick2d has a Vector2f class. But this is not allows operations with the vector. So i cant do this: direction = (target - pos).normalize(); – HUNeater Apr 13 '13 at 17:19
1

do direction = target.sub(pos).normalize(); – Axis Apr 13 '13 at 17:23
And what about this line: pos += direction * delta * bulletSpeed; ? – HUNeater Apr 13 '13 at 18:49
1

pos.add(direction.scale(delta * bulletSpeed)); – Axis Apr 13 '13 at 18:54
Everything seems good, but when i shoot, the bullet is created, but then the player moves with the shots. Im really confused now. – HUNeater Apr 13 '13 at 19:21
Update the link to your source with your new code and I will take a look at what you are doing. – Axis Apr 13 '13 at 20:17

Slick2d | Shooting with same speed

The problem:

2 Answers2