LookAt in opposite direction?

Question

I don't understand why 3dtext has backwards orientation, but I need to use transform lookat with the text mesh. I don't want to dump it in a another game object, I just need to look at the camera, without the letters being backwards! How do I reverse transform.LookAt?

Thanks alot!

Answer 1

Best Answer

Answer by superventure · Jun 21, 2011 at 12:11 AM

Found an answer after more browsing (sorry)

transform.LookAt(2 * transform.position - stareat.position);

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Bunny83 · Jun 21, 2011 at 12:15 AM 0

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Yep, that will work too ;)

aanimation · May 22, 2014 at 05:06 AM 0

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yeaah..thanks..its working

rodichan · Jan 28, 2016 at 09:38 PM 0

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Serious question: why does multiplying by two work? I've tried this solution in a project and don't understand the math behind it.

Thanks!

Bunny83 rodichan · Jan 29, 2016 at 03:18 AM 3

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Simple vector math. To get a direction vector from a point to another you do "target - start". In this case we calculate a direction vector from the object we want to look at (stareat.position) to our own position. So the resulting relative direction vector points towards us.

By adding our own position to that vector we let the direction vector start at our position. Since the direction points towards us it will be result in the position behind us.

ReverseLookAt

In this image we are the red dot (p1) and our second object is the green dot (p2). So instead of using p2 as lookat target we use p3 which is exactly behind us (the red dot). You get p3 by using the blue direction vector from p2 to p1 and adding it to p1.

 p1 + (p1-p2) == p1 + p1 - p2 == 2*p1 - p2

Another way to look at it is this:

reverselookat2

reverselookat.png (6.2 kB)

reverselookat2.png (3.2 kB)

Bunny83 · Jan 29, 2016 at 03:47 AM 1

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Maybe i should add that this solution is actually more complicated than mine below. LookAt most likely uses LookRotation internally. It simply subtracts it's own position from the given point to get a direction vector towards the target. So if you pass

 2 * transform.position - stareat.position

and LookAt subtracts transform.position from that given vector it would be

 2 * transform.position - stareat.position - transform.position

which is just

 transform.position - stareat.position

Answer 2

Answer by Bunny83 · Jun 21, 2011 at 12:14 AM

That will do what you want. It rotates the transform "away" from the target.

 var target : Transform;
 function Update ()
 {
     transform.rotation = Quaternion.LookRotation(transform.position - target.position);
 }

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yotingo · Jun 28, 2014 at 08:34 AM 0

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Thanks for this!

I was trying to figure out how to do it with Quaternion.LookRotation specifically. This works perfect!

I can't believe it was as simple as swapping the transform and the target.

LookAt in opposite direction?

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