A window can be moved even when some fingers are not over it

[Daniel d'Andrada]

Prerequisites:
A touchscreen device must be used (not trackpads)

Steps to reproduce the problem:
1 - lay 3 fingers on the display so that two of them are over a window but the third one is outside it, but not distant from it (in order for the centroid of the triangle described by those 3 touch points to still lie inside that window).
2 - right after after step 1, drag those 3 fingers over the display.

Expected outcome:
The window shouldn't move since one of the fingers is not inside it.

Actual outcome:
The window does move, following the gesture, since the centroid of the triangle described by those 3 fingers is inside that window.

[Mohamed IKBEL Boulabiar (boulabiar)]

>Expected outcome:
>The window shouldn't move since one of the fingers is not inside it.

Why this is the expected outcome ? Why we shouldn't move the window ?

[Chase Douglas (chasedouglas)]

Hi Ikbel,

On a touchscreen, if you put on finger over the target window and two other fingers over other windows, then the intention is ambiguous. Currently, the code looks at the centroid of the touches to determine which window to interact with. By requiring all the touches to hit the same window, we remove all ambiguity about which window is really targeted.

This is really a design decision. To me it makes sense. If you disagree, we can escalate this to the Unity designers and confirm which is correct according to their designs.

Thanks!

[Mohamed IKBEL Boulabiar (boulabiar)]

Hi Chase,

On Tue, Apr 17, 2012 at 9:19 PM, Chase Douglas
<email address hidden>wrote:

> On a touchscreen, if you put on finger over the target window and two
> other fingers over other windows, then the intention is ambiguous.
> Currently, the code looks at the centroid of the touches to determine
> which window to interact with. By requiring all the touches to hit the
> same window, we remove all ambiguity about which window is really
> targeted.
>

Yep, I remember a discussion about how to recognize this and the related
use of combinatorial gestures to avoid ambiguity.

> This is really a design decision. To me it makes sense. If you disagree,
> we can escalate this to the Unity designers and confirm which is correct
> according to their designs.
>

I've only found this decision strange as it has changed from the old point
of view.
You know that fingers are not always very well aligned on the
window/widget, and because of this some people invented the probabilistic
matching[1].
Anyway, some later end-user testing may confirm this decision to require
fingers inside the window.

Thanks for the answer and keep the good work !

[1] http://notjulie.com/research/probinput/paper.pdf

[Andrea Azzarone (azzar1)]

I cannot reproduce the bug on 16.04. Closing. Please reopen if you still can.