Moving a point (vector) on an angle + Libgdx

Question

i wanna move a point (Vector2) on an angle. i have my angle. but i'm not good in math or libgdx. for getting angle i use this :

degrees = (float) ((Math.atan2(touchPoint.x - x,
                -(touchPoint.y - y)) * 180.0d / Math.PI) + 240.0f);

now, i want to move vector. but i really don't know what i must do... i looked at questions but there was just somethings about changing angle, not transfer. i think there must be a function for this in libgdx. please help.

UPDATE :

public class Games implements ApplicationListener {

SpriteBatch spriteBatch;
Texture texture;
float x = 160;
float y = 5;

Vector2 touch;
Vector2 movement;
Vector2 position;
Vector2 dir;
Vector2 velocity;

float speed;
float deltaTime;

@Override
public void create() {
    spriteBatch = new SpriteBatch();
    texture = new Texture(Gdx.files.internal("images/1.png"));

    touch = new Vector2();
    movement = new Vector2();
    position = new Vector2();
    dir = new Vector2();
    velocity = new Vector2();

    speed = 5;
    deltaTime = Gdx.graphics.getDeltaTime();
}

public void render() {
    Gdx.gl.glClear(Gdx.gl10.GL_COLOR_BUFFER_BIT);
    deltaTime += 0.5f;

    spriteBatch.begin();

    begin(deltaTime);
    spriteBatch.draw(texture, position.x, position.y);

    spriteBatch.end();
}

private void begin(float deltaTime) {
    touch.set(Gdx.input.getX(), Gdx.input.getY());

    position.set(x, y);
    dir.set(touch).sub(position).nor();
    velocity.set(dir).scl(speed);
    movement.set(velocity).scl(deltaTime);
    position.add(movement);
}

Solution

If I am understanding your question correctly, you are looking for a direction vector?

If that is a correct understanding, you can do something like this:

// Declared as fields, so they will be reused
Vector2 position = new Vector2();
Vector2 velocity = new Vector2();
Vector2 movement = new Vector2();

Vector2 touch = new Vector2();
Vector2 dir = new Vector2();

// On touch events, set the touch vector, then do this to get the direction vector
dir.set(touch).sub(position).nor();

Which will give you a normalized direction vector from the position to the touch point.

You can then scale it to the speed you want to move, then use it to update your position.

velocity = new Vector2(dir).scl(speed);

And on each frame, do something like this

movement.set(velocity).scl(deltaTime);
position.add(movement);

---

Update

Here's how it would look like in a full class:

class Game extends ApplicationAdapter {

    Vector2 position = new Vector2();
    Vector2 velocity = new Vector2();
    Vector2 movement = new Vector2();
    Vector2 touch = new Vector2();
    Vector2 dir = new Vector2();

    Vector3 temp = new Vector3();

    float speed = 100;

    OrthographicCamera camera;

    SpriteBatch batch;
    Texture texture;
    Sprite sprite;

    @Override
    public void create () {
        camera = new OrthographicCamera();
        camera.setToOrtho(false);

        batch = new SpriteBatch();

        texture = new Texture(Gdx.files.internal("data/badlogicsmall.jpg"));

        sprite = new Sprite(texture);

        Gdx.input.setInputProcessor(new InputAdapter() {
            @Override
            public boolean touchDown (int screenX, int screenY, int pointer, int button) {
                camera.unproject(temp.set(screenX, screenY, 0));
                touch.set(temp.x, temp.y);
                return true;
            }
        });
    }

    @Override
    public void render () {
        Gdx.gl10.glClear(GL10.GL_COLOR_BUFFER_BIT);
        update(Gdx.graphics.getDeltaTime());
        batch.begin();
        sprite.draw(batch);
        batch.end();
    }

    @Override
    public void dispose() {
        texture.dispose();
        batch.dispose();            
    }
    public void update (float deltaTime) {
        position.set(sprite.getX(), sprite.getY());
        dir.set(touch).sub(position).nor();
        velocity.set(dir).scl(speed);
        movement.set(velocity).scl(deltaTime);
        if (position.dst2(touch) > movement.len2()) {
            position.add(movement); 
        } else {
            position.set(touch);
        }               
        sprite.setX(position.x);
        sprite.setY(position.y);
    }
}

Note, you could do away with the position Vector2 and just use the x and y directly, but I like to use use a Vector2 because it is a bit cleaner.

Comments

[Hosein]

i do what ever you said, but there is a problem. i can't reach to scl(...) method. what is the library's name for this method?

[Hosein]

that was my libs. i just download the latest version, and fixed. but it don't move. i update my code.

[Hosein]

so my problem was in deltaTime. i didn't update it. after update it worked well. tnx. p.s : but if you have a better way to update it just say it to me :D

[Hosein]

hmmm.... i don't know, but it didn't work for low place press. i mean if i click on places upper than 50 in work. but for x = 5 it don't work. it goes somewhere upper, not the right place.

[nEx.Software]

Updated my answer to show how this would look in a full class.

[Hosein]

that was perfect. thanks a lot. i know u answered my question. but can you comment the update function for me? i don't understand some of this codes. and another question, if i want to my texture start from another position (not 0, 0), where i must do that?

[Emre Koç]

You should change touch.set(temp.x, temp.y); to touch.set(temp.x-sprite.getWidth()/2, temp.y-sprite.getHeight()/2); for touch centered sprite