How is it possible to fade-out a TextButton after it has been pressed? - libgdx

Question

I simply want to fade-out (opacity = completely transparent) a button after I've pressed it... the following code has the unexplainable effect of fading the background image (a totally different actor!) to black !
What am I doing wrong ?
Skin skin = new Skin();
TextureAtlas buttonAtlas = new TextureAtlas(Gdx.files.internal("gfx/menu_buttons.pack"));
skin.addRegions(buttonAtlas);
TextButtonStyle textButtonStyle = new TextButtonStyle();
textButtonStyle.font = mButtonSpacefont;
textButtonStyle.up = skin.getDrawable("menu_button_background_top");
textButtonStyle.down = skin.getDrawable("menu_button_background_bottom");
mButtonStartGame = new TextButton("Play", textButtonStyle);
mButtonStartGame.setPosition(game.getIdealWidth()/2 - mButtonStartGame.getWidth()/2,
game.getIdealHeight()/2 - mButtonStartGame.getHeight()/2);
mButtonStartGame.addListener(new ChangeListener()
{
#Override
public void changed (ChangeEvent event, Actor actor)
{
//triggers when button is pressed and let go
mButtonStartGame.addAction(Actions.fadeOut( 1.0f ));
}
});
// add actors to stage
mStage.addActor(backgroundActor);//background
mStage.addActor(titleActor);//ontop of background
mStage.addActor(mButtonStartGame);//ontop of background
UPDATE 1:
I've discovered that the TextButton is faded out - BUT - so is the actor that contains the background image backgroundActor ! Why would the backgroundActor be faded when the code doesn't even call backgroundActor.addAction(Actions.fadeOut( 1.0f )); ??
UPDATE 2:
The render() method seems to play a part... when I call Gdx.gl.glClearColor(0, 0, 0, 0); the whole screen (except for the titleActor!) turns black due to the fadeOut action. When I call Gdx.gl.glClearColor(1, 1, 1, 1); the whole screen (except for the titleActor!) turns white.
#Override
public void render(float delta)
{
Gdx.gl.glClearColor(0, 0, 0, 0);//clear the screen black
//Gdx.gl.glEnable(GL20.GL_BLEND);// no effect, so commented out
Gdx.gl.glClear(GL20.GL_COLOR_BUFFER_BIT);
// update the actors
mStage.act(Gdx.graphics.getDeltaTime());
// draw the actors
mStage.draw();
}

Answer 1

The solution was that all of my actor's need to take into consideration the parentAlpha and set the color with batch.setColor().
Since my background was an actor, and I wasn't setting the batch color, the background was screwed up.
for example:
public class ActorBackground extends Actor
{
// Member Variables
private Texture mTexture;
// Constructor
public ActorBackground(GFXLoader gfxloader)
{
mTexture = new Texture(gfxloader.loadGraphic("menu_background"));// returns Gdx.files.internal(file.path())
//setBounds(getX(), getY(), mTexture.getWidth(), mTexture.getHeight());
setWidth(mTexture.getWidth());
setHeight(mTexture.getHeight());
}
#Override
public void draw(Batch batch, float parentAlpha)
{
// needed to make actions work
super.act(Gdx.graphics.getDeltaTime());
// needed to make fade work
Color color = new Color(this.getColor().r, this.getColor().g, this.getColor().b, this.getColor().a * parentAlpha);
batch.setColor(color);
// show it
batch.draw(mTexture, getX(), getY(), getWidth(), getHeight());
}
}