Check if pointer state touchID matches cached TouchControl touchID

Covers the edge case of releasing one finger and pressing with another in the same frame.

Author: jfreire-unity

Packages/com.unity.inputsystem/InputSystem/Plugins/UI/InputSystemUIInputModule.cs

@@ -1729,16 +1729,33 @@ private int GetPointerStateIndexFor(InputControl control, bool createIfNotExists
             // Determine the pointer (and touch) ID. We default the pointer ID to the device
             // ID of the InputDevice.
             var controlParent = control.parent;
+            // NOTE: m_PointerTouchControls stores references to TouchControl instances. e.g. this means that "touch0"
+            // in the same frame can have different touchId values.
             var touchControlIndex = m_PointerTouchControls.IndexOfReference(controlParent);
             if (touchControlIndex != -1)
             {
-                // For touches, we cache a reference to the control of a pointer so that we don't
-                // have to continuously do ReadValue() on the touch ID control.
-                m_CurrentPointerId = m_PointerIds[touchControlIndex];
-                m_CurrentPointerIndex = touchControlIndex;
-                m_CurrentPointerType = UIPointerType.Touch;
-
-                return touchControlIndex;
+                // Pointers are deallocated in the frame after their release (unpressed), which means the pointer state
+                // and the m_PointerTouchControls entry is only removed in the next frame
+                // (see UI_TouchPointersAreKeptForOneFrameAfterRelease).
+                // To accomodate for cases when touch is released and pressed in the same frame, the pointer
+                // state touchId needs to be checked against the cached touch control touchId (in m_PointerTouchControls)
+                // This is because the pointer state of the released touch (unpressed) still exists.
+                // If touchIDs are different, a new pointer should be allocated. Otherwise, a cached reference will
+                // be used.
+                var pointerTouchControl = m_PointerTouchControls[touchControlIndex];
+                ref var pointerState = ref GetPointerStateForIndex(touchControlIndex);
+
+                if (!(pointerTouchControl is TouchControl) ||
+                    (pointerTouchControl is TouchControl &&
+                     pointerState.eventData.touchId == ((TouchControl)pointerTouchControl).touchId.value))
+                {
+                    // For touches, we cache a reference to the control of a pointer so that we don't
+                    // have to continuously do ReadValue() on the touch ID control.
+                    m_CurrentPointerId = m_PointerIds[touchControlIndex];
+                    m_CurrentPointerIndex = touchControlIndex;
+                    m_CurrentPointerType = UIPointerType.Touch;
+                    return touchControlIndex;
+                }
             }
 
             var pointerId = device.deviceId;