WaitUntil Component

Here’s a little something that I hope to use increasingly in the future : elements of functional programming to facilitate modification of state over time or game loops, without using threads all over the place. It’s nothing new, and there are other solutions (like Nick Gravelyn’s Interpolators and Timers), but I tried to make it as concise and generic as I could.

Here it is, more comments after the listing.

using System;
using Microsoft.Xna.Framework;
using Microsoft.Xna.Framework.GamerServices;

namespace Foo
    public class WaitUntil : IGameComponent, IUpdateable
        public static Game Game { private get; set; }

        public static void GuideDisappears(Action onValid)
            Game.Components.Add(new WaitUntil(_ => !Guide.IsVisible, onValid));

        public static void TimePassed(float secondsToWait, Action onValid)
            Game.Components.Add(new WaitUntil(waited => (waited as TimeKeeper).Elapsed.TotalSeconds > secondsToWait,
                                              (elapsed, waited) => (waited as TimeKeeper).Elapsed += elapsed,
                                              onValid, new TimeKeeper()));
        class TimeKeeper { public TimeSpan Elapsed; }

        readonly Func<object, bool> condition;
        readonly Action<TimeSpan, object> whileWaiting;
        readonly Action onValid;
        readonly object state;

        WaitUntil(Func<object, bool> condition, Action onValid) : this(condition, ActionHelper.NullAction, onValid) { }
        WaitUntil(Func<object, bool> condition, Action<TimeSpan, object> whileWaiting, Action onValid) : this(condition, whileWaiting, onValid, null) { }
        WaitUntil(Func<object, bool> condition, Action<TimeSpan, object> whileWaiting, Action onValid, object state) 
            this.condition = condition;
            this.whileWaiting = whileWaiting;
            this.onValid = onValid;
            this.state = state;

        public void Update(GameTime gameTime)
            if (condition(state))
                whileWaiting(gameTime.ElapsedGameTime, state);

        #region Stuff we don't care about
        public void Initialize() { }
        public bool Enabled { get { return true; } }
        public event EventHandler EnabledChanged;
        public event EventHandler UpdateOrderChanged;
        public int UpdateOrder { get { return 0; } }

    public static class ActionHelper
        public static void NullAction<T, U>(T t, U u) { }

I ended up using basically a GameComponent, which means I need access to a Game instance to add it and remove it from the component collection. I decided to use a static field (that you assign in the Game’s constructor) to avoid passing it every time. It’s very unlikely that the Game instance will change or be destroyed… and I already static-ified it in my ServiceHelper earlier anyway.

I also wrote a couple (okay, two) static factory methods that are slightly fluent-interface-ey.

// (from the context of your Game class implementation)
    // Say "OK" when the guide stops being visible, like this?
    Components.Add(new WaitUntil(_ => !Guide.IsVisible, () => Console.WriteLine("OK!")));
    // ...or like this!
    WaitUntil.GuideDisappears(() => Console.WriteLine("OK!"));

    // And while we're at it...
void WaitForTwoSeconds()
    Console.WriteLine("Will wait for two seconds...");
    // ...recursive timers!
    WaitUntil.TimePassed(2, WaitForTwoSeconds);

I’ll probably add new factory methods as the needs arise, and make the class overall more useful, but I feel like it’s a good start.
I used the “GuideDisappears” method when a gamer signs out and I want to show a warning message using the Xbox Guide before going back to a sign-up screen… but since signing out is usually performed from the Guide itself, you have to wait for it to close before doing anything. This seemed like the simplest solution, and it works great.

Anaglyph Stereoscopic Rendering in First Person

I decided to finally finish up my analgyph stereoscopy sample, and cut the depth-of-field component that was adding too much complexity for my limited spare time right now.

stereoscopy finalstereoscopy final 2


Binaries : stereoscopy_bin.zip (1.9 Mb – Binaries)
Code : stereoscopy_src.zip (524 Kb – Source Only, get DLLs for TV3D and SlimDX from the Binaries)


This sample demonstrates a couple of things :

  • Optimized anaglyph filters for red/cyan stereoscopic rendering, to reduce eye-strain by minimizing retinal revialry but still keep some color information. As my source suggests, I’ve also implemented red channel gamma correction in the shader.
  • Auto-focus of both eyes on a focal plane. The camera is in the first person and the two “virtual cameras” act like human eyes, in the manner that they are connected to a single brain that wants to look at a single point. So the center of the screen is assumed to be that focal point, and both eyes will look at it. I used a depth rendering pass to achieve this, and a weighted sum of a certain portion of the screen near the center (this is all tweakable in realtime)

The distance between the eyes is also tweakable, if you want to give yourself a headache.

I wanted to do a stereoscopy sample to show how I did it in Super HYPERCUBE, but I can’t/don’t want to release its source, so I just re-did it properly. Auto-focus is a bonus feature that I wanted to play with; sHC didn’t need that since the focal plane was always the backing wall.

This sample, like all my recent ones, uses the latest version of my components framework. There are some differences between this release and the Stencil Rendering one, but it’s mostly the same. The biggest thing is that base components (Keyboard, Sound, etc.) are not auto-loaded anymore, and must be added in the Core.Initialize() implementation. This way, if I don’t need the sound engine, I just don’t load it… makes more sense.

Hope you like it!