S Pen Stopped Working After Unity Update

I have a Samsung Tablet with S Pen. I tried different methods to get input from it. New input system did not detect it as a pen, it was detected as a touch but it was really buggy so I discarded this option. After numerous tries, I managed to get it work in Unity 2020.3.1 using this code piece:

Code (CSharp):

1.             if (Input.GetMouseButton(0))
2.                 Vector3 touchPos = _mainCamera.ScreenToWorldPoint(Input.mousePosition);
3.  

Mouse position was changing while I was dragging the S Pen and moving the object in the scene as I wanted.

However, I updated to Unity 2020.3.18 and suddenly S Pen is not working as expected. After debugging, I realised that Mouse Position is only updated when it first touches the screen. While dragging, its value is always constant. GetMouseButton(0) still returns true thus detects the S Pen. Only when I press the button on S Pen the mousePosition value starts to get updated.

Did Unity modified Input methods in recent updates? Is there a workaround for this problem?

 

@berkc ran into the same issue. Have you ever found a solution?

Input.mousePosition stops updating when the S-Pen touches the screen / mouse button down is registered. Unity 2020.3.18f1

 

I have submitted a bug report ( case 1370814 )

Currently I'm trying to get around this by recalculating Input.mousePosition in the update cycle and then using a static MyGame.mousePosition instead of Input.mousePosition.

But it's not satisfactory results, it's a bit lagging behind or overshooting here and there.

Code (CSharp):

1.  
2. public class MyGame : MonoBehaviour
3. {
4.     #if UNITY_ANDROID
5.     Vector2 mousePresPos = Vector2.zero;
6.     Vector2 lastMousePos = Vector2.zero;
7.     static public Vector2 mousePosition = Vector2.zero;
8.  
9.     public void updateMousePos() {
10.         Vector2 mousePos = Input.mousePosition;
11.  
12.         if(mousePos != mousePresPos) {
13.             mousePresPos = mousePos;
14.             lastMousePos = mousePos;
15.             yAccumulatedInput = 0;
16.             xAccumulatedInput = 0;
17.         }else{
18.             var mx = Input.GetAxis("Mouse Y");
19.             var my = Input.GetAxis("Mouse X");
20.             if(mx != 0 || my != 0) {
21.                 xAccumulatedInput += mx;
22.                 yAccumulatedInput += my;
23.                 lastMousePos.x = mousePos.x + (yAccumulatedInput * 15f);
24.                 lastMousePos.y = mousePos.y + (xAccumulatedInput * 15f);
25.             }
26.         }
27.         mousePosition = lastMousePos;
28.     }
29.     #else
30.     static public Vector2 mousePosition {
31.         get {
32.             return Input.mousePosition;
33.         }
34.     }
35.     #endif
36.  
37.     void Update() {
38. #if UNITY_ANDROID
39.        updateMousePos();
40. #endif
41.        // ...
42.     }
43. }
44.  

 

If we would have a source code reference on how

Input.mousePosition

is calculated based on

Input.GetAxis("Mouse Y"); Input.GetAxis("Mouse X");

or

Input.GetAxisRaw("Mouse Y"); Input.GetAxisRaw("Mouse X");

then we could implement a work-around for this bug.

But I was not able to find any references on how

Input.mousePosition

is calculated. My code above was the closest I got to it, but I think it may be lacking small amounts of data in a few frames, or my estimated multiplier may be off by a tiny bit. Currently it's set to

15f

based on experimentation.

In our Input settings for the project, Mouse X / Y are set to sensitivity 0.1.

 

Also not sure if related, but

Input.GetAxis("Mouse ScrollWheel")

seems to be getting weird values with S-Pen, causing a lot of zoom ins/outs. Would be interesting to see how to detect if we're actually connected to a S-Pen to disable it, but keep it enabled for a "proper" mouse.

Would be great if we could get S-Pen support working, as it seems many other players in bigger games are begging for such support - https://us.forums.blizzard.com/en/hearthstone/t/fix-the-s-pen-in-android-version-of-the-game/27315 and https://www.reddit.com/r/hearthston..._it_will_be_one_year_without_s_pen_error_fix/ - so demand for proper S-Pen support is there.

It's also weird that S-Pen is recognized as a mouse, and not simply as a touch and that

Input.stylusTouchSupported

returns false ( or is it unrelated? ).

 

Bug was accepted and fixed in 2022.1.0a3.
They are evaluating requests for backporting the fix to 2019.4, 2020.3, 2021.1, and 2021.2. So leave a comment if that's interesting for you :

https://issuetracker.unity3d.com/is...ng-when-the-s-pen-is-used-on-a-samsung-device

 

I already left comment in issue, but maybe we can have someone from Unity side to comment on expected time we see fix ported to 2020.3 LTS?