Details
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Bug
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Resolution: Unresolved
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P2: Important
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None
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6.5.3, 6.6.1, 6.8.0
Description
Dragging multiple items from within a flickable can produce inaccurate values in centroid.pressPosition. The issue happens when the touch point for the multiple items are started at the same time. The issue does not occur if the items are picked one by one or when the Flickable's interactivity is turned off or when only one finger is used (or equivalently when only one item is dragged). The scenePosition is also consistently (0, 0) in the second DragHandler when queried from within onCentroidChanged. The issue has been verified occurring on Android and also on Windows and Linux albeit a little bit more inconsistently.
To reproduce the issue please run the attached example project.
When you drag one of the red rectangles, a green rectangle having the coordinates corresponding the pressPosition will appear on the screen. Dragging one item is fine and the green rectangle appears underneath the finger. Dragging two items with simultaneous touch presses causes one of the green rectangles to be places way outside the expected range. Dragging with 3 fingers causes 2 items to be dragged correctly and their centroid to have the expected values, but the third item does not get dragged at all.