Make in-view center point CSS pixel aware #1319
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The outer groups are a distraction.
It's misleading to use multiplication by 0.5 since you wouldn't implement the in-view center point like this. Instead divide by 2.0, which makes it clear that we expect the result to be a floating point.
Calculating the centre point of a square may produce a decimal precision number. Given a 1x1 px square the center point will be (0.5,0.5), but the DOM operates in integer CSS pixels. Rounding the number would get us the closest positive integer, or 1. However, the coordinate (1,1) is beyond the bounding box of the square. This means we need to floor the number to ensure we always get a click point that is within the client rect of the element. An additional complexity is that not all web platform APIs treat floating point numbers the same way. DOMElement.elementsFromPoint, which we use for getting the paint tree to determine if the web element is interactable, will floor the number which deems the element interactable. However, in Gecko, nsIDOMUtils.sendMouseEvent ceils the number, causing the actual click point to fall beyond the square.
andreastt
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AutomatedTester,
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shs96c
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andreastt
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AutomatedTester
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Oct 19, 2018
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Quoting the commit message of the last patch:
Tests will be provided as part of https://bugzilla.mozilla.org/show_bug.cgi?id=1499360, which implements this in geckodriver.