atan2 - find angle between two points (360deg)

Question

I have a game where there is a Player and some enemies. These enemies, just as the player itself, can shoot bullets. But the angle of bullets don't change as it is supposed to; The newly created bullet is supposed to find the angle between itself and the player, then just go in that direction - this has to be done in 360° .

I have followed this answer but I believe that I have done something incorrect.

because this is what happens:

and this is how it should be:

currently it only goes like this:

This is the part of code which takes care of X & Y of bullets:

angle = Math.atan2(Game.getPlayerY(), Game.getPlayerX()) - Math.atan2(getY(), getX());
if (angle < 0) 
    angle += 2 * Math.PI;
setX((getX()+(float)(Math.sin(angle)))-Config.BulletSpeed);
setY((getY()+(float)(Math.cos(angle)))-Config.BulletSpeed);

How do I make the Bullets go in a certain angle?

I guess you mean cos for one of the sets (you use sin for both). — Andy Turner, Sep 15 '18 at 11:05
I changed to sin & cos but that didn't help, it only goes in a diagonal way as shown above — Feelsbadman, Sep 15 '18 at 11:09
one of them should use cos, one should use sin. But I don't think you are calculating the angle correctly either, it should be more like `atan2(y2-y1, x2-x1)`. — Andy Turner, Sep 15 '18 at 11:17
For better help sooner, post a [MCVE] or [Short, Self Contained, Correct Example](http://www.sscce.org/). — Andrew Thompson, Sep 16 '18 at 00:04

Andy Turner · Answer 1 · 2018-09-15T12:51:40.327

1

Honestly, I think you are over-complicating it by using angles. All you seem to be wanting to do is to move a bullet along the vector between the two objects at a given speed.

All you have to do for this is to normalize the vector. The length of the line between the two things is given by:

double dx = Game.getPlayerX() - getX();
double dy = Game.getPlayerY() - getY();
double len = Math.hypot(dx, dy);

So you can use this to calculate a scale factor for the bullet speed:

double s = Config.BulletSpeed / len;

Then just use this in your expression to update x and y:

setX((getX()+dx*s);
setY((getY()+dy*s);

edited Sep 15 '18 at 12:51

answered Sep 15 '18 at 12:44

Andy Turner

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It is not supposed to follow the player like a rocket which follows a target. If I am at (23, 23) and the bullet is created at (100, 53) the bullet should travel a straight line between these two and continue for as long as it can. Imagine a real gun, you point it somewhere and shoot it. If target moves, bullet wont follow it. – Feelsbadman Sep 15 '18 at 12:51
@IdontReallywolf then why does your expression involve `Game.getPlayerX()` and `getX()` (and for y)? – Andy Turner Sep 15 '18 at 12:55
I am trying to get that angle between the two points :D but obviously i have 0 knowledge of this – Feelsbadman Sep 15 '18 at 12:57

clabe45 · Answer 2 · 2018-09-17T18:49:41.293

I agree with Andy's answer; you really only need a normalized vector between the two points, instead of an angle. But if you need an angle, you just form the vector between the two points, and then use Math.atan2:

let velocity = new Vector(target.x - source.x, target.y - source.y);
let angle = Math.atan2(velocity.y, velocity.x);

Then, if you need the x or y step, from the source to the target, normalize the vector, and then just use velocity.x and velocity.y:

// normalize
let magnitude = Math.sqrt(velocity.x*velocity.x + velocity.y*velocity.y);  // distance formula for length of vector
velocity.x /= magnitude;
velocity.y /= magnitude;

// scaled to speed you want
velocity.x *= SPEED;
velocity.y *= SPEED;

You don't need to derive the vector from the angle that you derived from the vector.

EDIT: As Topaco pointed out in the comments, to add a realistic touch, add the source velocity to the final velocity:

velocity.x += source_velocity.x
velocity.y += source_velocity.y

atan2 - find angle between two points (360deg)

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