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I need to find the angle of rotation from a bullet traveling from point A to point B, like in my attached diagram. I tried searching, but I got a little lost in which exact formula to use.
I want to find the direction of a bullet, expressed as a vector with X and Y coordinates.
In your situation you need a simple subtraction, with a normalization.
vectDistance = B - A
vectDirection = vectDistance / lenght(vectDistance)
This will give you the direction.
In LibGDX, you can use the sub method from the Vector2 class, along with the nor from the same class:
vectDirection = b.sub(a).nor();
To help figure out if you need to subtract A from B or B from A, try to translate (in your mind) the 'origin' to (0, 0), and move the 'target' along with it. From that perspective, the "direction" should be taken from the position of the 'target'.
Another clue that will make you notice that you used the wrong order: the bullets will fly in the opposite direction of what you're expecting ;P
sub method, along with the nor method. The sub method will give you the vector from A to B. This vector contains 2 things: the direction and the distance. You don't need the distance, so you need to normalize this vector. To do so you use the nor method, which will normalize it, i.e. give you a unit vector, i.e. a vector of length 1.
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OK thanks to the help of this community (above) Here is actually how I implemented it:
public Bullet(Texture texture, Vector2 startPosition, Vector2 targetPosition){
super(texture);
setSize(0.1f,1f);
setPosition(startPosition.x, startPosition.y);
direction = targetPosition.sub(startPosition);
direction.nor();
System.out.println("direction " + direction.x + "," + direction.y);
}
public void update(float delta){
setPosition(getX() + (direction.x * speed), getY() + (direction.y * speed));
}
This works with the player character standing near the middle of the screen, it will fire bullet anywhere around him that I press. Thanks
B - A? \$\endgroup\$