Rotate gyroscope-based camera over it's Y axis by swiping

Questions & Answers
1

Hello everyone,

Im trying to rotate the camera based on a user’s swipe, normally it would be quite simple(yRotation=xSwipe) but my camera is based on the gyroscope which causes the game-world to stay straight relative to the real world no matter what the device orientation is. When swiping, I only want to rotate the camera over it’s Y axis so the world still stays straight no matter how you swipe.

88151-swipe-to-rotate-problem.jpg
88151-swipe-to-rotate-problem.jpg960×720 37.3 KB

The gyroscope based camera already works but the swiping part does not. The problem is that the concept of “horizontal swipe” can be on both/either the X and/or Y axis on the screen.

The orientation Unity player setting is set to landscape so if you hold your device like the bottom phone of the image, a horizontal swipe would be on the screen-space X axis, if you hold your device like the top-left phone, a horizontal swipe would be on the screen-space Y axis, and if you hold your phone like the top-right phone, a horizontal swipe would be on both the screen-space X and Y axis, and if you hold your phone upside down, a horizontal swipe would even be on the negative-y axis.

I have tried, sketched and visualized a lot of situations but I can not come up with a way that works mathematically to allow this rotation by swiping, perhaps it’s my lack of knowledge of quaternions or vector arithmetic or simply the limits of my imagination.

The properties I can work with are the swipe vector(x & y distance in pixels within a frame), the camera rotation which could be used as both a Quaternion or Euler angle and the camera up-vector. However I do not know how to convert/superimpose this X and Y movement in a way that considers the “up” of the camera.

Can someone help me out? Anything helps!

3

I’ve partially solved it by placing a spherical mesh collider with normals aiming inwards around the camera and writing this code(still messy but I’ll optimize it when it works):

void Update()
	{
		RaycastHit hit1, hit2;
		Vector3 begin = Vector3.zero, end = Vector3.zero;
		float angle1, angle2;

		if(Input.GetMouseButtonDown(0))
		{
			//get initial
			initialRay = Camera.main.ScreenPointToRay(Input.mousePosition);
			Debug.Log("Started swiping");
		}
		if(Input.GetMouseButton(0))
		{
			//get current
			updateRay = Camera.main.ScreenPointToRay(Input.mousePosition);
			//rotate
			Collider collider = GetComponentInParent<Collider>();
			if(collider.Raycast(initialRay, out hit1, 2f))
			{
				begin = hit1.point;
			}
			if(collider.Raycast(updateRay, out hit2, 2f))
			{
				end = hit2.point;
			}
			angle1 = Mathf.Atan2(begin.z - transform.position.z, begin.x - transform.position.x) * Mathf.Rad2Deg;
			angle2 = Mathf.Atan2(end.z - transform.position.z, end.x - transform.position.x) * Mathf.Rad2Deg;
			transform.Rotate(transform.parent.up, angle2 - angle1, Space.World);
			//reset initial
			initialRay = updateRay;
		}
		if(Input.GetMouseButtonUp(0))
		{
			Debug.Log("Stopped swiping");
		}
	}

It works very good but there’s only one problem left, when you click somewhere and move the mouse or your finger to a different location on your screen and stop moving there while holding your mouse or finger on the screen, the rotation shakes all the time between two positions, I would expect it to do nothing because the initial ray and update ray would be exactly the same but for some reason it shakes. I’ll take a look at it and return when I find a fix.

Thanks

2

@Cambesa, your camera tilts, but screen’s coordinate system stays fixed relative to the phone.

We need to make the coordinate system follow the tilt, not the phone.

//re-specify the coordinate of the touch as being relative to the center of the screen, not the bottom left corner of the phone.
Vector2 centerPos =  Input.touch[0].position - new Vector2(Screen.width, Screen.height) *0.5f ;

Quaternion gyro_rot = Input.gyro.attitude;

//we are only interested in rotation around the phone's perpendicular axis, which "sticks-out"
//http://answers.unity3d.com/questions/434096/lock-rotation-of-gyroscope-controlled-camera-to-fo.html
Quaternion referenceRotation = Quaternion.identity;
 Quaternion deviceRotation = DeviceRotation.Get();
 Quaternion eliminationOfXY = Quaternion.Inverse(
     Quaternion.FromToRotation(referenceRotation * Vector3.forward, 
                               deviceRotation * Vector3.forward)
 );
 Quaternion rotationZ = eliminationOfXY * deviceRotation;



Vector2 rotatedTouchPos =  rotationZ * centerPos;

I think this should work. If not try:

Quaternion.Inverse(rotationZ) * centerPos;