LibGDX - managing zoom

Question

Zooming an OrtographicCamera effectively changes the amount of world units that can be shown in the camera window. Should thus the camera viewport dimensions be correspondingly updated upon zoom? For example,

...
camera.zoom -= 0.01;
camera.viewportWidth *= camera.zoom;
camera.viewportHeight *= camera.zoom;
camera.update();
...

EDIT: Here's the full code:

private float CAMERA_WIDTH = 50;
private float CAMERA_HEIGHT = 50;
camera = new OrthographicCamera(CAMERA_WIDTH,CAMERA_HEIGHT);
camera.position.set(CAMERA_WIDTH / 2, CAMERA_HEIGHT / 2, 0);
camera.update();
// prints 1.0, 50.0, 50.0   --> OK
System.out.println(camera.zoom + ", " + camera.viewportWidth + ", " + camera.viewportHeight);
...

camera.zoom += 0.1;
camera.update();
// prints 1.1, 50.0, 50.0   --> NOT Ok
System.out.println(camera.zoom + ", " + camera.viewportWidth + ", " + camera.viewportHeight);
...

Executive summary: if you need the zoomed camera viewportWidth and viewportHeight, maintain them as separate variables. They must not be changed in the camera otherwise zoom calculation messes up (obviously, since the zoom is relative to the values the camera was created with, so the original values are always needed). If you absolutely want or need to reassign camera.viewportWidth and camera.viewportHeight, you have to reset camera.zoom to 1 immediately after.

Answer 1

The camera viewport width and height do not need updated after the camera zoom is changed as this is done already inside the update method.

The OrthographicCamera update method:

@Override
public void update (boolean updateFrustum) {
    projection.setToOrtho(zoom * -viewportWidth / 2, zoom * (viewportWidth / 2), zoom * -(viewportHeight / 2), zoom
        * viewportHeight / 2, near, far);
    view.setToLookAt(position, tmp.set(position).add(direction), up);
    combined.set(projection);
    Matrix4.mul(combined.val, view.val);

    if (updateFrustum) {
        invProjectionView.set(combined);
        Matrix4.inv(invProjectionView.val);
        frustum.update(invProjectionView);
    }
}

After your camera has been updated you should then update your rendering system such as spritebatch to use the new values with:

    cam.update();
    batch.setProjectionMatrix(cam.combined);