I'm new to libgdx, and I am finding I am getting stumped by the simplest of things. It seems to want me to do things a specific way, but the documentation won't tell me what that is.

I want to make a very simple 2d game in which the player controls a spaceship. The mouse wheel will zoom in and out, and information and controls are displayed on the screen.

But I can't seem to make the mouse wheel NOT zoom the UI. I've tried futzing with the projection matrices in between

Here's my (current) code:

public class PlayStage extends Stage {
...
    public void draw() {
    // tell the camera to update its matrices.
    camera.update();

    // tell the SpriteBatch to render in the
    // coordinate system specified by the camera.
    spriteBatch.setProjectionMatrix(camera.combined);

    spriteBatch.begin();

    aButton.draw(spriteBatch, 1F);

    playerShip.draw(spriteBatch, 1F);

    spriteBatch.end();
}
}

camera.zoom is set by scrolled(int amount).

I've tried about a dozen variations on the theme of changing the camera's projection matrix after the button is drawn but before the ship is, but no matter what I do, the same things happen to both the button and the ship. So:

What is the usual libgdx way of implementing an on-screen UI that isn't transformed by the camera's projection matrix/zoom?