Bug PointerMoveEvent.localPosition returns incorrect value

When installing two events on a VisualElement, `PointerDownEvent` and `PointerMoveEvent`, and printing `ev.localPosition` in both of them, I get the following output when I click and move my mouse just a few pixels:

Down: (912.87, 176.55, 0.00)

Move: (912.87, 447.90, 0.00)

I am implementing a virtual joystick for mobile but this bug prevents me from doing so, unless I am missing something. I will post the code below in case it's my fault or someone knows a workaround.

Put this script on the same GameObject that has the `UIDocument` component. The document must contain a root VisualElement that covers 100% of the screen, a child element called "JoystickContainer" that covers maybe 1/2 half of the screen (area where the joystick can be used), and that container must have two children "JoystickBackground" and "JoystickHandle" that are just two images with the same size.

Code (CSharp):

1. using System.Collections;
2. using System.Collections.Generic;
3. using UnityEngine;
4. using UnityEngine.UIElements;
5.  
6. public class JoystickUI : MonoBehaviour
7. {
8.     public float joystickRadius = 150f;
9.     public Vector2 initialLocalPosition = new Vector2(180f, 450f);
10.  
11.     VisualElement joystickBackground;
12.     VisualElement joystickHandle;
13.     Vector2 backgroundLocalPosition;
14.     Vector2 handleLocalPosition;
15.  
16.     // If the joystick is controlled by the user right now.
17.     bool isActive;
18.     int activePointerId;
19.  
20.     void Start()
21.     {
22.         UIDocument document = GetComponent<UIDocument>();
23.         VisualElement root = document.rootVisualElement;
24.  
25.         VisualElement joystickContainer = root.Query("JoystickContainer");
26.         joystickContainer.RegisterCallback<PointerDownEvent>(ev => OnPointerDown(ev));
27.         root.RegisterCallback<PointerUpEvent>(ev => OnPointerUp(ev));
28.         root.RegisterCallback<PointerMoveEvent>(ev => OnPointerMove(ev));
29.  
30.         joystickBackground = root.Query("JoystickBackground");
31.         joystickHandle = root.Query("JoystickHandle");
32.         SetBackgroundPosition(initialLocalPosition);
33.         SetHandlePosition(initialLocalPosition);
34.     }
35.  
36.     void SetBackgroundPositionCentered(Vector2 localPosition)
37.     {
38.         backgroundLocalPosition = localPosition;
39.  
40.         joystickBackground.style.left =
41.             backgroundLocalPosition.x - joystickBackground.resolvedStyle.width / 2f;
42.         joystickBackground.style.top =
43.             backgroundLocalPosition.y - joystickBackground.resolvedStyle.height / 2f;
44.     }
45.  
46.     void SetHandlePositionCentered(Vector2 localPosition)
47.     {
48.         handleLocalPosition = localPosition;
49.  
50.         joystickHandle.style.left =
51.             handleLocalPosition.x - joystickHandle.resolvedStyle.width / 2f;
52.         joystickHandle.style.top =
53.             handleLocalPosition.y - joystickHandle.resolvedStyle.height / 2f;
54.     }
55.  
56.     void SetBackgroundPosition(Vector2 localPosition)
57.     {
58.         backgroundLocalPosition = localPosition;
59.  
60.         joystickBackground.style.left = backgroundLocalPosition.x;
61.         joystickBackground.style.top = backgroundLocalPosition.y;
62.     }
63.  
64.     void SetHandlePosition(Vector2 localPosition)
65.     {
66.         handleLocalPosition = localPosition;
67.  
68.         joystickHandle.style.left = handleLocalPosition.x;
69.         joystickHandle.style.top = handleLocalPosition.y;
70.     }
71.  
72.     void OnPointerDown(PointerDownEvent ev)
73.     {
74.         if (isActive)
75.             return;
76.  
77.         isActive = true;
78.         activePointerId = ev.pointerId;
79.         SetBackgroundPositionCentered(ev.localPosition);
80.         SetHandlePositionCentered(ev.localPosition);
81.         Debug.Log("Down: " + ev.localPosition);
82.     }
83.  
84.     void OnPointerUp(PointerUpEvent ev)
85.     {
86.         if (ev.pointerId != activePointerId || !isActive)
87.             return;
88.  
89.         isActive = false;
90.         SetBackgroundPosition(initialLocalPosition);
91.         SetHandlePosition(initialLocalPosition);
92.     }
93.  
94.     void OnPointerMove(PointerMoveEvent ev)
95.     {
96.         if (ev.pointerId != activePointerId || !isActive)
97.             return;
98.        
99.         // Demonstrate that `ev.localPosition` returns a wrong value.
100.         SetHandlePositionCentered(ev.localPosition);
101.         Debug.Log("Move: " + ev.localPosition);
102.     }
103. }

 

Thanks a lot! I totally missed that.

Yes they are the same, it's not a bug. Thanks again.