Setting up custom motors for motion

[DrKillingerParticipant]

Hi guys

I was wondering if it’s possible to set up a custom motor script in Rain? I’m busy checking Rain out to see if my current project will work well. I love what I see so far, but I have a set of very specific motor scripts for various types of vehicles (tanks, hovercraft, etc) with their own acceleration and turning behaviours.

In short, is it possible to port my code as a motion in Rain, and if so, can someone perhaps point me in the right direction in the API to get a handle on doing so?

Thanks!

Edit: It struck me that I might just use a custom script to replace “move”. Would this be preferable?

Edit2: Never mind. All was answered after diving through the API a bit. I might be back later for guidance, but so far things seem great.

• This topic was modified 1 year, 8 months ago by  DrKillinger. Reason: Symantics
• This topic was modified 1 year, 8 months ago by  DrKillinger.
• This topic was modified 1 year, 8 months ago by  DrKillinger.

[primeKeymaster]

Yes, you can absolutely set up a Custom Motor. You can start by overriding BasicMotor and just modifying the Move and Face methods. Here are some things to keep in mind:

The job of the Motor is to
a) Grab the current state of the Body in UpdateMotionTransforms. This usually equates to copying Transform data in the the AI Kinematic
b) Modify the AI Kinematic state based on Move and Face. Do this however you want. The BasicMotor uses instantaneous velocities calculated from trying to follow paths generated by the Navigator. These velocities are set into the Kinematic.
c) Apply Kinematic changes back to the Body in ApplyMotionTransforms. This usually equates to calling Kinematic.UpdateTransformData and then copying Kinematic position and rotation back into the Body transform.

Here’s how that looks in BasicMotor

/// <summary>
        /// UpdateMotionTransforms updates the AI Kinematic structure with the current
        /// values associated with the AI Body.
        /// </summary>
        public override void UpdateMotionTransforms()
        {
            _ai.Kinematic.Position = _ai.Body.transform.position;
            _ai.Kinematic.Orientation = _ai.Body.transform.rotation.eulerAngles;
            _ai.Kinematic.ResetVelocities();
        }
        /// <summary>
        /// ApplyMotionTransforms applies physical forces back to the AI Body
        /// </summary>
        public override void ApplyMotionTransforms()
        {
            _ai.Kinematic.UpdateTransformData(_ai.DeltaTime);
            _ai.Body.transform.position = _ai.Kinematic.Position;
            _ai.Body.transform.rotation = Quaternion.Euler(_ai.Kinematic.Orientation);
        }

[DrKillingerParticipant]

Thanks so much Prime! I actually found my embarrassing mistake last night and got the custom motor into Rain. Right now, I’m just looking at how I’m supposed to manipulate the parent transform to move and rotate.

is _ai.Body the parent GameObject?

[primeKeymaster]

Yes, _ai.Body (or AI.Body) is the game object the AI should be moving.

[DrKillingerParticipant]

Well bugger me, it works! Refactoring my tracked and wheeled vehicle code now, thanks for the help!

[DrKillingerParticipant]

In terms of BasicMotor, is Face() called from within Move()? I see the API describes Move() as having many operations, including “…turning to face the target, etc.”.

[primeKeymaster]

Face is not called from within Move, but it is called by the Behavior Tree Move node. By default, if no separate Facing target is set, the BasicMotor will try to turn the Character to face forward while moving.

[DrKillingerParticipant]

Ok, I ask because if I override the Move() function, Face() seems to not work anymore.

Looking through Kinematic, should I manipulate Position directly to move as I’d like? Here’s some testing code, and when I use it I lose Face functionality:

public override bool Move()
{
	_ai.Kinematic.Position += (_ai.Kinematic.Forward*2*Time.deltaTime);	
	return false;
}

Why would this cause Face() to not try and face the target anymore? (I’m inheriting from BasicMotor, by the way). Sorry if I haven’t understood.

While I’m at it, does Rain have a quick way of determining degrees to face a target, so that I can implement something similar to the Default Face Before Move Angle? I have a function for determining this, but maybe Rain has something to make my code a bit more concise.

• This reply was modified 1 year, 8 months ago by  DrKillinger.

[primeKeymaster]

Your code will have no impact on Face(). However, it is best not to change Kinematic.Position directly. That’s because other functions, including Face, use Kinematic.Position as part of their own calculations. Those methods should be able to assume that Kinematic.Position represents the current AI position, not the one you want in the future.

That’s why you should do something more like

_ai.Kinematic.Velocity = _ai.Kinematic.Forward * 2f * _ai.DeltaTime;

and then call UpdateTransformData in ApplyMotionTransforms as in the code I posted. I also recommend you use AI.DeltaTime instead of Time.deltaTime.

Take a look at the SimpleSteering class and Utility.MathUtils for helper functions.

[DrKillingerParticipant]

Maybe I’m being thick, but if I only override Move() and make it always move forward, it should still be turning to face my moveTarget, while always moving in a forward direction:

public class CustomMotor : BasicMotor
{
	public override bool Move()
	{
		_ai.Kinematic.Velocity = _ai.Kinematic.Forward * defaultSpeed * _ai.DeltaTime;
		return false;
	}
}

But when I do this, it only moves forward. No steering or pathfinding occurs. Any idea as to why this would happen? Sorry for bothering you.

• This reply was modified 1 year, 8 months ago by  DrKillinger.
• This reply was modified 1 year, 8 months ago by  DrKillinger.

[primeKeymaster]

That example isn’t meant to be your complete solution. You also need to decide how you are going to deal with turning.

If this is a vehicle solution, then forward (or reverse) velocity is all you get. Next, add rotation to the solution based on the turn rate of your vehicle. This would be a change to _ai.Kinematic.Orientation. Just adjust the Y rotation +/- some degrees. On subsequent frames the forward velocity will be in a new direction and turning can occur.

Here’s an example of simple movement (non vehicle)

public override bool Move()
        {
            if (IsAt(moveTarget))
                return true;
            _ai.Navigator.pathTarget = moveTarget;
            MoveLookTarget target = _ai.Navigator.GetNextPathWaypoint(Allow3DMovement);
            SimpleSteering.DoDirectMovement(_ai, target.Value, CloseEnoughDistance, CloseEnoughAngle, FaceBeforeMoveAngle, Allow3DMovement, Allow3DRotation);
            return false;
        }

[DrKillingerParticipant]

Oooooooooh… I thought Face() dealt with the turning side of things. Everything’s working now. Thanks for the effort, I really appreciate it.

[DrKillingerParticipant]

If you’re still checking this thread, I have a public function in my motor that returns whether the AI is walking or running, but not sure how to access it from another script. Any advice?

[primeKeymaster]

The motor is always accessible from AI.Motor. If is is your custom motor, it would be something like:

MyMotor tMotor = AI.Motor as MyMotor;
bool walking = tMotor.IsWalking;

If you are running in code that doesn’t have access to the AI directly, then you’ll need something like:

AIRig tRig = gameObject.GetComponent<AIRig>();
MyMotor tMotor = tRig.AI.Motor as MyMotor;

[primeKeymaster]

Face() does deal with the turning side of things if you have a separate faceTarget set on the motor. However, the BasicMotor automatically tries to turn the AI toward the forward direction during the Move call.

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