osu-lazer/osu.Game/Screens/BackgroundScreenStack.cs

// Copyright (c) ppy Pty Ltd <contact@ppy.sh>. Licensed under the MIT Licence.
// See the LICENCE file in the repository root for full licence text.

using System.Collections.Generic;
using osu.Framework.Graphics;
using osu.Framework.Screens;

namespace osu.Game.Screens
{
    public partial class BackgroundScreenStack : ScreenStack
    {
        public BackgroundScreenStack()
            : base(false)
        {
            RelativeSizeAxes = Axes.Both;
            Anchor = Anchor.Centre;
            Origin = Anchor.Centre;
        }

        /// <summary>
        /// Attempt to push a new background screen to this stack.
        /// </summary>
        /// <param name="screen">The screen to attempt to push.</param>
        /// <returns>Whether the push succeeded. For example, if the existing screen was already of the correct type this will return <c>false</c>.</returns>
        public bool Push(BackgroundScreen? screen)
        {
            if (screen == null)
                return false;

            bool isFirstScreen = CurrentScreen == null;
            screen.AnimateEntry = !isFirstScreen;

            if (EqualityComparer<BackgroundScreen>.Default.Equals((BackgroundScreen?)CurrentScreen, screen))
                return false;

            base.Push(screen);

            return true;
        }
    }
}