How can I apply a force to an object (eg, a rolling ball) in the direction that the camera is facing?

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Hi to all,

My player comes up to a point where he enters his vehicle in a tunnel, kind of like a subway system.

If I roll my ball on the first straightaway, the controls are going to react properly. Meaning up:moves forward, down:moves backwards, right:moves right and left:moves left. But as soon as I turn as I hit the first turn and no matter if I have some straightaways further ahead, the ball no longer react to the controls I'm sending him resulting in up:moves left, down:moves right, left:moves forward and right:moves backwards.

I've went through unityAnswer/unityForum but I can't find anything on this. I've tried AddTorque, AddForce

Is there a way of making sure that no matter what trajectory my "subway system" has, that the ball will react correctly to the up, down, left and right key?

Would it be possible to use the coordinates of the camera instead or something like that?

Answer 1

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Answer by duck · Apr 21, 2010 at 09:47 AM

To add a force to the ball in the direction that the camera is pointing, use this:

rigidbody.AddForce( camera.transform.forward * speed );

However, often your camera isn't pointing exactly horizontal in relation to your game, so you may want to remove the tilt angle of your camera before using its direction. Eg, if your camera is looking "across but angled down a bit", you don't want your force to be applied in the down direction at all. You can fix that by zeroing the Y value of the camera's forward transform before using it:

Javascript:

var forceDirection = camera.transform.forward;
forceDirection.y = 0;
rigidbody.AddForce( forceDirection.normalized * speed );

C#:

Vector3 forceDirection = camera.transform.forward;
forceDirection = new Vector3( forceDirection.x, 0, forceDirection.y );
rigidbody.AddForce( forceDirection.normalized * speed );

In order for this to provide you with good gameplay controls, you should make it so that your camera continues to follow the object and rotates according to the object's velocity direction.

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maparizeau · Apr 21, 2010 at 03:07 PM 0

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I will try it out. and get back to you on this.

maparizeau · Apr 21, 2010 at 06:32 PM 0

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It worked great. But I only had to use the following...

for up/down rigidbody.AddForce((useObject.transform.forward speed) inputX);

and left/right rigidbody.AddForce((useObject.transform.right speed) inputY);

thanks!

duck ♦♦ · Apr 21, 2010 at 07:08 PM 0

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Yes it will work like that if your camera stays relatively horizontal in relation to the surface - my other examples we in case your camera can end up looking down on the ball, when it might cause problems.

cynamiter.du · Jul 01, 2010 at 09:24 PM 0

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I tried this on my project, but I always get the following error: ,,$$anonymous$$issingComponentException: There is no 'Camera' attached to the "Player" game object, but a script is trying to access it. You probably need to add a Camera to the game object "Player". Or your script needs to check if the component is attached before using it.

controller2.Update () (at Assets\controller2.js:146)" Even if the camera is attached to the "Player"-object, I'm getting this error...

I know this is a quite old post, but the script works for me. Exept the "zeroing the Y value"-part. :(

Answer 2

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Answer by HolBol · Apr 20, 2010 at 09:17 PM

Try using

AddRelativeForce

Then forward will always be forward in relation to the ball's position, same for left right etc.

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maparizeau · Apr 20, 2010 at 09:48 PM 0

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Hi Fishman92,

The problem with using AddRelativeForce is that as soon as the ball starts turning and you keep pressing the up button to move forward, the balls starts to go backwards and then forward. So you end up staying in place. Or is there something that I can use that will leave the coordinates in their original position even when the ball is rolling? I will post my scrip if you need to look at it.

HolBol · Apr 21, 2010 at 03:22 PM 0

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Oh... well worked for me :S

How can I apply a force to an object (eg, a rolling ball) in the direction that the camera is facing?

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