The Instruction Limit

I think that XNA’s implementation of the XInput API for Xbox 360 controllers is terrific. Simple, complete, ready to use. So when I wanted to add gamepad support (including analog input and vibration) to Super HYPERCUBE, a TV3D 6.5 game, I just added a reference to the XNA Framework assembly and carried on like I did in Fez. But I realize that referencing XNA just for controller support is silly, and I don’t want to assume that it’s installed on clients, nor force-install the redistributable.

So I recently looked for a more proper solution. It looks like MDX 2.0 Beta had support for XInput, but it’s been discontinued in favor of XNA for some time. There is also a handful of managed wrappers around the XInput native DLL that use P/Invokes… wasn’t too keen on that either.

Then I recalled that SlimDX is the community-maintained successor to MDX, and that it’s awesome. And as a matter of fact, it has complete support for XInput! So might as well use that.

But SlimDX is, well, slim. It’s a very thin wrapper and doesn’t do any normalization or dead zone detection for thumbsticks. It’s not much of a bother to do yourself, but I figured I’d post my code as a reference to people who want to use SlimDX’s XInput implementation in the real world.

Details

My dead zone code is based around the “Getting Started With XInput” guide on MSDN, but given the C#3/SlimDX beautifying treatment.
I also found that analog triggers on my controllers did not need dead zones, but if you want to use them as binary buttons, you can check against the appropriate SlimDX constant.

My “state class” does not wrap everything that the SlimDX Controller class exposes, like voice support, battery information, etc. So I made the local Controller instance a public readonly member, and you can access it to query whatever other information you need. Or of course you can add the getters/state variables that you need.

Download

GamepadState.cs (C#3 – 5 Kb, SlimDX March 2009 SP1 SDK or later needed)

Just the dead zone code

If you’re only looking for that, here it is :

    var gamepadState = Controller.GetState().Gamepad;
    var leftStick = Normalize(gamepadState.LeftThumbX, gamepadState.LeftThumbY, Gamepad.GamepadLeftThumbDeadZone);
    var rightStick = Normalize(gamepadState.RightThumbX, gamepadState.RightThumbY, Gamepad.GamepadRightThumbDeadZone),
}
 
static Vector2 Normalize(short rawX, short rawY, short threshold)
{
    var value = new Vector2(rawX, rawY);
    var magnitude = value.Length();
    var direction = value / (magnitude == 0 ? 1 : magnitude);
 
    var normalizedMagnitude = 0.0f;
    if (magnitude - threshold > 0)
        normalizedMagnitude = Math.Min((magnitude - threshold) / (short.MaxValue - threshold), 1);
 
    return direction * normalizedMagnitude;
}

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