1499360 - WebDriver:ElementClick unable to click 1x1 px element

Status: RESOLVED FIXED

(Remote Protocol :: Marionette, enhancement, P1)

Description

[Andreas Tolfsen ❲:ato❳]

See description and reproducible test case in
https://github.com/mozilla/geckodriver/issues/1402

This could also be a specification problem.

Comment 1

[Andreas Tolfsen ❲:ato❳]

I did some investigation into this and it looks like a rounding
error in the specification.  When the element has an odd shape that
can’t be divided in two without a precision point, it fails to ceil
the centre point to the nearest integer.

For example, given a 1x1 rectangle the centre point would be at
(0.5,0.5).  The click synthesise code will accept this input and
pass it on to the event queue without question, but since it is not
a valid pixel it ceils the coordinates and instead clicks (0,0).
Conversely, if the rectangle is 9x9 where the centre point is
(4.5,4.5) it will click (5,5).

Comment 2

[Henrik Skupin [:whimboo][⌚️UTC+1]]

That reminds me at https://stackoverflow.com/questions/10825926/python-3-x-rounding-behavior whereby this is Javascript.

Comment 3

[Andreas Tolfsen ❲:ato❳]

(In reply to Henrik Skupin (:whimboo) from comment #2)

> That reminds me at
> https://stackoverflow.com/questions/10825926/python-3-x-rounding-behavior
> whereby this is Javascript.

I’m glad you told me about that because I was just writing a
(Python) WPT test case that ran into this problem.  Using the math
to call out which way to round seems to work fine though.

Comment 4

[Andreas Tolfsen ❲:ato❳]

Attachment: bug 1499360: marionette: convert in-view centre point to css pixels;

When the in-view centre point contains a floating point, we need to
ensure to convert it to CSS pixels before passing it on to Gecko internals
such as DOMElement.elementsFromPoint and DOMWindowUtils.sendMouseEvent.

For example, with a click target that is a 1x1 square, the in-view
centre point prior to this patch was calculated to (0.5,0.5).
elementsFromPoint will (correctly?) round this coordinate down and
return the paint tree for the DOM element at (0,0) coordinates.

By contrast, sendMouseEvent will click coordinates (1,1) because it
rounds up.  To make sure we all speak the same language internally,
we round the centre point down.

Comment 5

[Andreas Tolfsen ❲:ato❳]

Attachment: bug 1499360: webdriver: write in-view centre point tests;

These tests are not exhaustive, but covers some of the main use
cases and known edge cases.

Depends on D8880

Comment 6

[Andreas Tolfsen ❲:ato❳]

Attachment: bug 1499360: webdriver: add interactability test for zero-sized element;

Depends on D8881

Comment 7

[Pulsebot]

Pushed by [e-mail]:
https://hg.mozilla.org/integration/autoland/rev/ae99f2ef9464
marionette: convert in-view centre point to css pixels; r=whimboo
https://hg.mozilla.org/integration/autoland/rev/d51f52d435da
webdriver: write in-view centre point tests; r=whimboo
https://hg.mozilla.org/integration/autoland/rev/6afa28099f1e
webdriver: add interactability test for zero-sized element; r=whimboo

Comment 8

[Web Platform Test Sync Bot [:wpt-sync] (Matrix: #interop:mozilla.org)]

Created web-platform-tests PR https://github.com/web-platform-tests/wpt/pull/13655 for changes under testing/web-platform/tests

Comment 9

[Sebastian Hengst [:aryx] (needinfo me if it's about an intermittent or backout)]

https://hg.mozilla.org/mozilla-central/rev/ae99f2ef9464
https://hg.mozilla.org/mozilla-central/rev/d51f52d435da
https://hg.mozilla.org/mozilla-central/rev/6afa28099f1e

Comment 10

[Web Platform Test Sync Bot [:wpt-sync] (Matrix: #interop:mozilla.org)]

Upstream PR merged