Android/Libgdx How to fix this issue?

Question

Currently iam programming on a game where you move a spaceship and try to avoid asteroids. The spaceship should move when the user touches it and so follow the finger movement of the user. The spaceship is a sprite that moves arround with:

if (Gdx.input.isTouched()) {  

    x = Gdx.input.getX() - width / 2;
    y = -Gdx.input.getY() + height / 2;

} 

The problem that i'm having right now is that the user can teleport the spaceship by touching the screen. How can i fix this? Is it possible to set a touch region?

Answer 1

Calculate a unit vector direction from the ship to the touch point and multiply that by a speed. You need to convert touch coordinates to world coordinates by unprojecting with the camera.

private static final float SHIP_MAX_SPEED = 50f; //units per second
private final Vector2 tmpVec2 = new Vector2();
private final Vector3 tmpVec3 = new Vector3();

//...

if (Gdx.input.isTouched()) {  
    camera.unproject(tmpVec3.set(Gdx.input.getX(), Gdx.input.getY(), 0)); //touch point to world coordinate system.
    tmpVec2.set(tmpVec3.x, tmpVec3.y).sub(x, y); //vector from ship to touch point
    float maxDistance = SHIP_MAX_SPEED * Gdx.graphics.getDeltaTime(); //max distance ship can move this frame
    if (tmpVec2.len() <= maxDistance) {
        x = tmpVec3.x;
        y = tmpVec3.y;
    } else {
        tmpVec2.nor().scl(maxDistance); //reduce vector to max distance length
        x += tmpVec2.x;
        y += tmpVec2.y;
    }
}