libgdx vector2: shooting ball at an angle

java, libgdx

Solution

I'd do something like this, assuming you are shooting the ball from its current position (or any known position really) toward the touched position:

public class Snippet extends ApplicationAdapter {

    ShapeRenderer renderer;
    OrthographicCamera camera;

    Ball ball = new Ball();

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

    @Override
    public void render () {
        Gdx.gl.glClear(GL10.GL_COLOR_BUFFER_BIT);

        ball.update(Gdx.graphics.getDeltaTime());

        renderer.setProjectionMatrix(camera.combined);
        renderer.begin(ShapeType.Line);
        renderer.setColor(1.0f, 1.0f, 1.0f, 1.0f);
        renderer.circle(ball.position.x, ball.position.y, ball.radius);

        // Show the travel path of the ball if we were to click at the current location.
        if (Gdx.app.getType() == ApplicationType.Desktop || Gdx.app.getType() == ApplicationType.WebGL) {
            renderer.setColor(0.2f, 0.2f, 0.2f, 1.0f);
            renderer.line(ball.position.x, ball.position.y, Gdx.input.getX(), Gdx.graphics.getHeight()- Gdx.input.getY());          
        }
        renderer.end();

        if (Gdx.input.justTouched()) {
            // Invert the the y to accommodate difference in coordinate systems
            ball.shootToward(Gdx.input.getX(), Gdx.graphics.getHeight()- Gdx.input.getY());
        }
    }

    class Ball {

        public float speedMax = 350;

        public float radius = 10;
        public Vector2 position = new Vector2();
        public Vector2 velocity = new Vector2();

        /** Shoot the ball toward the designated position */
        public void shootToward(float targetX, float targetY) {
            /*
             * Get the normalized direction vector from our position to the target. Then scale that value to our desired speed. In
             * this particular example, we are using the distance of the target from the current position to determine how fast we
             * will shoot the ball, and limiting to a maximum speed. We will apply velocity in the update method.
             */
            velocity.set(targetX - position.x, targetY - position.y).nor().scl(Math.min(position.dst(targetX, targetY), speedMax));
        }

        public void update(float deltaTime) {
            position.add(velocity.x * deltaTime, velocity.y * deltaTime);
            velocity.scl(1 - (0.98f * deltaTime)); // Linear dampening, otherwise the ball will keep going at the original velocity forever
        }

    }

    public static void main(String[] args) {
        new LwjglApplication(new Snippet2());
    }

}

Problem

Original source