Strange top-down rotation problem.

Unity Engine
1

I’ve got a small problem trying to do a very simple random roaming script for a top down game.
My object should move forward, then every second rotate a bit, but continue to move where is facing.
The script is on an empty GameObject which is father to my mesh.
It goes like that:

#pragma strict
var speed:float=3;
var changeDir:float=1;
private var timer: float;

function Start()
{
	timer = changeDir;
}
	
function Update() {
	
	transform.Translate(transform.forward * Time.deltaTime * speed);
	if (timer>0)
		timer-=Time.deltaTime;
	else 
	{
		transform.RotateAround(transform.position, Vector3.up, 10);

		timer = changeDir;
	}
}

the problem is the facing direction doesn’t look to be in sync with the rotation: my object changes the movement direction, but it doesn’t go towards where it’s facing. So it ends doing all the strangest things (like walking backwards).

Where I’m wrong?
Thanks!

2

try this:
use Vector3.forward instead of transform forward. Also, no need to rotate around the transform position. You can use rotate.

#pragma strict

var speed:float=3;
var changeDir:float=1;
private var timer: float;

function Start()

{
    timer = changeDir;
}

    

function Update() 
{ 

    transform.Translate(Vector3.forward * Time.deltaTime * speed);

    if (timer>0)
        timer-=Time.deltaTime;
    else 
    {
        transform.Rotate(Vector3.up, 10);
        timer = changeDir;
    }
}
3

Thank you so much!
Since I’m a complete newbie, can you explain me what’s the difference between vector3.forward and transform.forward?
Thanks again!

4

Vector3.forward is world direction. transform.forward is the direction where the transform (i.e your player) is looking at.

5

Well, shouldn’t be more correct, in my code, to use transform, then? Since I’m rotating the character, shouldn’t the forward direction be relative to the player rather than to the world?
[Sorry if this seems stupid, I really need to understand how the transforms work]

6

Well, transform.Translate works a bit different than if you mess directly with positions.

By default is will convert the translation parameter to Local space, unless otherwise specified.

From the documentation

function Update() {
    // Move the object forward along its z axis 1 unit/second.
    transform.Translate(Vector3.forward * Time.deltaTime);

    // Move the object upward in world space 1 unit/second.
    transform.Translate(Vector3.up * Time.deltaTime, Space.World);
}

    transform.Translate(Vector3.forward * Time.deltaTime);

    // should be equal to 
    transform.position = transform.position + transform.forward * Time.deltaTime;
    // or
    transform.position = transform.position + transform.TransformDirection(Vector3.forward) * Time.deltaTime;


...
    transform.Translate(Vector3.forward * Time.deltaTime, Space.World);

    // should be equal to the one above
    transform.position = transform.position + Vector3.forward * Time.deltaTime;

The Translate method is just here to make it easier for people, as it will do the world to local space translations for you.

7

Ok, that’s much clearer, now.
Thank you!