Fix firing ChangeListener on onGroundProperty() with setScaleX()

[monjasa]

It seems like chaning X scale (it doesn't matter whether the change includes sign change such as from +1 to -1, it still apears, for instance, from +1 to +0.5) invokes a shift of PhysicsComponent's onGroundProperty.

[AlmasB]

Changing the scale of an entity affects its physics shape, which in turn requires the physics world to re-create the fixtures used in collision checks. When previous fixtures are removed, the onGround property becomes false since there is no fixture. Then when a new fixture is created, this triggers the onGround property to become true. So this is not a bug per se.

The above re-creation is necessary since even with just scaleX = -1 asymmetric hitboxes will need to be recalculated.

I don't have a clean solution to this yet, so I'll need some time to think. Any ideas?

[monjasa]

For my problem (exclude triggering with mirroring but keep with jumping) I've used a boolean variable . Inside jump() method I've got something like if (!jumping) jumping = true; if the entity isOnGround() (its physics component with a ground sensor), and then add new ChangeListener with overridden method:

public void changed(ObservableValue<? extends Boolean> observable, Boolean wasOnGround, Boolean isOnGround) {
    if (!isOnGround && wasOnGround && jumping) {
        System.out.println("jumping...");
    } else if (isOnGround && !wasOnGround && jumping) {
        System.out.println("on ground");
        jumping = false;
    }
}

I mean, maybe it's possible to add kind of 'lock'. But I guess it's neither thread-safe nor applicable without a loss of performance due to checking and saving such a variable.