OnDrag is not invoked with a small dragging movement in Unity

Question

I implemented mobile rotation control with IPointerDownHandler and IDragHandler. It seems fine if the movement is fast enough, but there's a serious flaw that the OnDrag event never invoked if the dragging amount is very tiny.

Here's the code.

using UnityEngine; using UnityEngine.EventSystems; [RequireComponent(typeof(CanvasGroup))] public class MobileFPSRotationPanel : MonoBehaviour, MobileFPSUIElement, IPointerDownHandler, IDragHandler, IEndDragHandler { ... public void OnDrag(PointerEventData eventData) { Debug.Log("Drag"); <- It's not invoked if the dragging is too small. eventData.Use(); Vector2 currentTouchPosition = eventData.position; m_Movement = currentTouchPosition - m_PreviousTouchPosition; m_PreviousTouchPosition = currentTouchPosition; } public void OnEndDrag(PointerEventData eventData) { Debug.Log("EndDrag"); m_Pressing = false; m_Movement = Vector2.zero; } public void OnPointerDown(PointerEventData eventData) { Debug.Log("PointerDown"); if (Interactable == false) { return; } eventData.Use(); m_Pressing = true; m_Movement = Vector2.zero; m_PreviousTouchPosition = eventData.position; } ... }

I reported a lot of people have been annoyed by this glitch, which makes it hard to precise aiming. Is this a glitch or an intended feature of Unity? If it's intended, then how should I detect every drag movement even if it's super tiny?

Using Unity 2019.4.3f1.

Mangata · Accepted Answer · 2022-05-29 15:04:54Z

You can simply set the drag threshold of the event system:

The Drag Threshold property represents the number of pixels a UI object can be moved before it is considered being "dragged". People don't have perfectly steady hands, so when they are trying to click or tap a UI item their mouse or finger may move slightly. This Drag Threshold allows the player to move their input slightly (or a lot if you make this number high) before the item they are selecting is being "dragged" rather than "clicked".

Or you can simulate the drag yourself by update():

using UnityEngine; using UnityEngine.EventSystems; [RequireComponent(typeof(CanvasGroup))] public class MobileFPSRotationPanel : MonoBehaviour, IPointerDownHandler, IPointerUpHandler { private bool isDragging; void Update() { if (!isDragging) { return; } OnPointerMove(Input.mousePosition); } public void OnPointerMove(Vector3 position) { Debug.Log(position); } public void OnPointerDown(PointerEventData eventData) { isDragging = true; } public void OnPointerUp(PointerEventData eventData) { isDragging = false; } }

you can also add IPointerMoveHandler interface instead of Update method and custom OnPointerMove method — MarsPeople
– MarsPeople, Commented Apr 7, 2023 at 23:57

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