Restricting Movement in 2D

Unity Engine
1

Hello

I’m sorry if this is a re-post but I have looked through the forums and have been unable to find a solution to my problem. I am trying to restrict an object to move only in the X-Y plane, as the game is a simple 2D scrolling. I have attached a Rigidbody component and the object moves from the left edge of the screen to the right, with a hidden cube placed in the centre to stop it passing off screen. The input is from the mouse not the keyboard.

I have modified a script I found on the wiki site

function FixedUpdate ()
{

	// Get the input and set variables for it
	horizontal = -Input.GetAxis("Mouse X"); 
	vertical = Input.GetAxis("Mouse Y");

	horizontal *= force;
	vertical *= force;
	

	if(rigidbody.velocity.magnitude < maxspeed))
	{
		//cancel out the forces in the Z direction
		// * It is relative to the camera
		// * we remove the z component because we really want to apply forces only on the 2D plane
		var up = transform.TransformDirection(Vector3.up);
		up.z = 0;
		rigidbody.AddForce (up * vertical); 
		
	
		var right = transform.TransformDirection(Vector3.right);
		right.z = 0;
		rigidbody.AddForce (right * horizontal);

                Debug.Log(transform.rotation);


	} 
}

When I check the transform using the debug I can still see values in the Z axis. A quick fix was to modify the Camera Mouselook C# script, clamp the rotation of my Rigidbody object. But the movement is somewhat jerky as I’m sure the two scripts are fighting each other…

    rotationY += Input.GetAxis("Mouse Y") * sensitivityY;
    rotationY = ClampAngle (rotationY, minimumY, maximumY);

    Quaternion yQuaternion = Quaternion.AxisAngle (Vector3.left, Mathf.Deg2Rad * rotationY);
    transform.localRotation = originalRotation * yQuaternion;

I’m sure I’m making a mess of what should be a simpler solution. Any help greatly appreciated.

2

You can add this at the end of the script:
transform.position = new Vector3(transform.position.x, 0.0f, transform.position.z);

Rigidbody should be used only for physics simulation, if you need to move a object with the mouse it’s easier to add vectors to transform.position

3

We had a pretty good experience using a ConfigurableJoint attached to each object that should only move in two dimensions - just need to attach the component, set ZMotion to “Locked,” and then AngularXMotion and AngularYMotion to “Locked” as well (since we also only wanted rotations about the z axis.

4

You also want it to be configured in world space. Or just put this script in the Assets/Editor folder and use the 2D menu it makes.

@MenuItem ("2D/Move Onto 2D Plane ^2")
static function MoveOnto2DPlane () {
	for (var transform in Selection.transforms) {
		transform.position.z = 0;
	}
}

@MenuItem ("2D/Move Onto 2D Plane ^2", true)
static function ValidateMoveOnto2DPlane () {
	return (Selection.activeTransform != null);
}

@MenuItem ("2D/Make Selection 2D Rigidbody")
static function MakeSelection2DRigidbody () {
	MoveOnto2DPlane();
	
	for (var transform in Selection.transforms) {
		var rigidbody : Rigidbody = transform.GetComponent(Rigidbody);
		
		if (!rigidbody)
			transform.gameObject.AddComponent(Rigidbody);
		
		var configurableJoint : ConfigurableJoint = transform.GetComponent(ConfigurableJoint);
		
		if (!configurableJoint)
			configurableJoint = transform.gameObject.AddComponent(ConfigurableJoint);
		
		configurableJoint.configuredInWorldSpace = true;
		configurableJoint.xMotion = ConfigurableJointMotion.Free;
		configurableJoint.yMotion = ConfigurableJointMotion.Free;
		configurableJoint.zMotion = ConfigurableJointMotion.Locked;
		configurableJoint.angularXMotion = ConfigurableJointMotion.Locked;
		configurableJoint.angularYMotion = ConfigurableJointMotion.Locked;
		configurableJoint.angularZMotion = ConfigurableJointMotion.Free;
	}	
}

@MenuItem ("2D/Make Selection 2D Rigidbody", true)
static function ValidateMakeSelection2DRigidbody () {
	return (Selection.activeTransform != null);
}

Cheers,
-Jon

5

Jon, saved as what … “2D/Move Onto 2D Plane.cs” ??

6

It’s Jon. 8) I have mine saved as Assets/Editor/TwoDHelper.js .

Cheers,
-Jon

7

I knew that of course. Just bad typing today.

8

I’m trying to do something similar but having issues.

I’m trying to allow an object to rotate in all three dimensions but not move along the z plane. I borrowed some of the code here as I was also getting jerking motion previously.

How can I throw out movement along one plane but allow all the other physics to continue?

9

Take a look at the script I posted above. Just modify which axis are locked and free to what you want.

-Jon