Choosing a random wander direction | Official Unity Discord | Page 1

kind plover Aug 19, 2023, 4:47 PM

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I've got entities that need to wander around the world, and I want to model random but also semi-directed behavior. What I'd prefer is a behavior that picks a random forward vector within a range of forward vectors relative to the entity's current forward direction. What is a good way to pull this off? I've tried rotating the entities forward vector in pos/neg directions and lerping between them randomly to find the new forward direction, but I'm not getting it to work, and I don't know enough about Unity's vectors to figure out the correct approach.

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`public override Vector3 GetDestination(Ant ant)
{
// should calculate travel radius based on ant speed and choose a random point within that radius
Vector3 up = ant.transform.up;

    Vector3 leftVector = Quaternion.AngleAxis(100, up) * up;
    Vector3 rightVector = Quaternion.AngleAxis(-100, up) * up;
    Vector3 guessDirection = Vector3.Lerp(leftVector, rightVector, Random.Range(0f, 1f));

    // in the meantime:
    Vector3 destination = ant.transform.position + guessDirection * 1;
    Debug.Log("Ant" + ant.id + ": " + guessDirection + ", " + ant.transform.position + ", " + destination);
    return destination;
}

`

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ant.transform.up is the ant's actual forward direction, since I'm currently just using a Capsule object on its side.

agile portal Aug 19, 2023, 4:53 PM

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    {
        return antPosition + Quaternion.Euler(0, Random.Range(0, 360), 0) * Vector3.forward * distance;
    }```

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do u mean like

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something like that?

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ohhh ant.transform.up

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u need it relative to the ants .up direction

kind plover Aug 19, 2023, 4:54 PM

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Yes, but I could do Random.Range(-30, 30) to get a 60 degree arc from ant.transform.up?

kind plover Aug 19, 2023, 4:55 PM

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agile portal u need it relative to the ants .up direction

yes

agile portal Aug 19, 2023, 4:55 PM

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kind plover Yes, but I could do `Random.Range(-30, 30)` to get a 60 degree arc from ant.tran...

you would need to take the ants euler angle

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like this

kind plover Aug 19, 2023, 4:55 PM

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I am learning about quaternions and angles etc but it's a bit much to learn lol

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Basically, the ant needs to choose a direction in this range in front of it: \/, where "front" is "up" lol

visual thistle Aug 19, 2023, 4:56 PM

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Create a random angle-axis rotation

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If this is 2D, then use the Z axis

kind plover Aug 19, 2023, 4:56 PM

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visual thistle Create a random angle-axis rotation

it is 3D

agile portal Aug 19, 2023, 4:56 PM

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    private Vector3 randomWanderTarget(float distance, Vector3 antPosition, Quaternion antRotation, float wanderRange)
    {
        Vector3 targetOffset = Quaternion.Euler(antRotation.eulerAngles + new Vector3(0, Random.Range(-wanderRange, wanderRange), 0)) * Vector3.forward * distance;
        return antPosition + antRotation * targetOffset;
    }

visual thistle Aug 19, 2023, 4:57 PM

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in 3D: var rot = Quaternion.AngleAxis(Random.Range(-30, 30), transform.up)

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this will be a random rotation between -30 and 30 degrees around the ant's local up vector

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you can then apply this rotation to a vector

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rot * transform.forward

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this will be a new vector rotated by up to 30 degrees

kind plover Aug 19, 2023, 4:58 PM

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visual thistle this will be a random rotation between -30 and 30 degrees around the ant's local...

now how do I ensure the rotation is along the correct plane, though? because couldn't it just as well rotate the up vector up/down as well as left/right or anything at all, really?

visual thistle Aug 19, 2023, 4:58 PM

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That's why you use AngleAxis

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it produces a rotation around an axis

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If the ant spins around its up vector (which is usually what you're doing in 3D), then this will randomly rotate the ant horizontally

kind plover Aug 19, 2023, 4:59 PM

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Is this even the best approach? Is angles/rotations costly? Compared to some sort of vector shortcut to produce the desired direction vector? I try to avoid linear algebra lol

visual thistle Aug 19, 2023, 4:59 PM

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it's fine.

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the math is pretty simple (for your computer)

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You could also just add a random vector to your forward vector and normalize it

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This doesn't give you a precise angle range.

kind plover Aug 19, 2023, 5:00 PM

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visual thistle If the ant spins around its up vector (which is usually what you're doing in 3D)...

ohhhhhh, this makes sense. I do not want to rotate around the up axis of the ant. I want to rotate the up axis itself about the effective up axis

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the ant is a capsule on it's side. so up is the direction it walks, and the effective up is either x or z depending on the capsule's rotation about the actual up axis (y)

visual thistle Aug 19, 2023, 5:00 PM

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Vector3 offset = 0.2f * Random.insideUnitSphere;
offset = Vector3.ProjectOnPlane(offset, transform.up);
transform.forward = transform.forward + offset;

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this would perturb the forward vector by uh

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a small amount

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i'm not sure what angles that'd give you

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the ProjectOnPlane throws out the part in the up direction

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so that the resulting offset vector only works in the local X and Z directions

visual thistle Aug 19, 2023, 5:02 PM

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kind plover the ant is a capsule on it's side. so up is the direction it walks, and the effe...

Just make the model a child of the actual Ant object

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That way its rotation is irrelevant

kind plover Aug 19, 2023, 5:02 PM

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visual thistle Just make the model a child of the actual Ant object

do you mind saying more? what model?

visual thistle Aug 19, 2023, 5:03 PM

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the capsule.

kind plover Aug 19, 2023, 5:03 PM

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you mean instead of having the capsule be a component of the ant object, have it be a child?

visual thistle Aug 19, 2023, 5:03 PM

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make the object with the mesh renderer a child of the actual Ant object

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yes

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it sounds very annoying to have to keep the thing rotated correctly so that the capsule stays on its side

kind plover Aug 19, 2023, 5:03 PM

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And this means that I just set the child's orientation when I need and use the Ant's own forward/up to orient it when needed?

kind plover Aug 19, 2023, 5:04 PM

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visual thistle it sounds very annoying to have to keep the thing rotated correctly so that the ...

100% lol

visual thistle Aug 19, 2023, 5:04 PM

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set the child's orientation once

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so that the capsule is on its side

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then control the parent's orientation as it moves around

kind plover Aug 19, 2023, 5:06 PM

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ok let me ask a little more then. i'm still learning. the Ant GameObject can have its own transform component to track it's movement and the Ant can also have a 3D model (composite or just a capsule) with it's own transform to determine its orientation?

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but i do want the ant to face the direction it is traveling, so when updating the ants direction, i would also want to update the model's direction?

visual thistle Aug 19, 2023, 5:07 PM

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Every GameObject has a transform.

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The capsule object is going to be a child of the Ant.

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That means that its parent's transform gets applied to it as well, basically

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Rotate the parent 90 degrees, rotate the child 90 degrees

kind plover Aug 19, 2023, 5:08 PM

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visual thistle That means that its parent's transform gets applied to it as well, basically

ah i see

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i think

visual thistle Aug 19, 2023, 5:08 PM

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If you put the child at [5,0,0] relative to its parent

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and then spin the parent

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the child will trace out a circle around its parent

kind plover Aug 19, 2023, 5:08 PM

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ok so ant.transform.up would not equal ant.model.transform.up, but that's ok, because relatively it all works out

visual thistle Aug 19, 2023, 5:08 PM

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Right.

kind plover Aug 19, 2023, 5:08 PM

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got it

visual thistle Aug 19, 2023, 5:08 PM

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transform.up is your local up vector

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+Y in local space

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in world space, it depends on your rotation

kind plover Aug 19, 2023, 5:09 PM

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visual thistle in world space, it depends on your rotation

yes this is what is giving me trouble lol

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i think i got it now

kind plover Aug 19, 2023, 6:18 PM

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is there best practice for managing scale, etc? i mean, i've added an AntModel child (just a capsule for now) to the Ant object. Do I set the scale for the parent or the child? It seems like there must be a better strategy for tuning those values than just guessing and checking. lol

visual thistle Aug 19, 2023, 6:22 PM

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I would resize the child.

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It's nice to have [1,1,1] on the parent by default

kind plover Aug 19, 2023, 6:23 PM

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makes sense

visual thistle Aug 19, 2023, 6:44 PM

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if you want to change the propotions, then definitely change the child's size

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non-uniform scaling causes problems for child objects

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specifically when they rotate

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they wind up getting skewed

kind plover Aug 19, 2023, 11:26 PM

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it looks like my parent transform and my child transform diverge from each other on collision with another object. how do you fix the child transform to always be the parent transform?

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easy to fix by making the child rigidbody kinematic, but i do want collisions to occur.

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i can also fix it by adding a rigidbody component to the parent object (which i wasn't doing previously). but the behavior is so much more strange when there's a rigidbody on the parent as opposed to when there is only a kinematic rigidbody on the child. the ants seem to jump from destination to destination, as opposed to gliding there when there's no rigidbody

visual thistle Aug 20, 2023, 12:49 AM

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If you're using a rigidbody, you must tell the rigidbody to move

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rather than just setting the transform directly

visual thistle Aug 20, 2023, 12:49 AM

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kind plover i can also fix it by adding a rigidbody component to the parent object (which i ...

Rigidbody.MovePosition would be what you want

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or just setting the velocity of the rigidbody

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the child shouldn't have an RB

kind plover Aug 20, 2023, 12:53 AM

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https://docs.unity3d.com/ScriptReference/Rigidbody.MovePosition.html

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can i not access the rigidbody component of a particular object with this.rigidbody? why GetComponent?

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Like why does ant.transform work?

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Why don't you have to GetComponent<Transform>()?

visual thistle Aug 20, 2023, 3:41 AM

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Every GameObject is guaranteed to have a Transform

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and every Component is guaranteed to be on a GameObject

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so every Component can also be guaranteed to have a Transform

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hence the property

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you aren't guaranteed to have a Rigidbody.

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Unity DID used to have some other properties for common components

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light, renderer, etc.

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but these are long gone

kind plover Aug 20, 2023, 4:13 PM

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ok but presumably the parent object also needs a mesh as well?

kind plover Aug 20, 2023, 4:32 PM

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hell yeah i've got some behavior i finally like

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lol that took forever

visual thistle Aug 20, 2023, 10:34 PM

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kind plover ok but presumably the parent object also needs a mesh as well?

No, since it’s not responsible for the visuals

#Choosing a random wander direction