1437019 - Autoscrolling: handle the case where vertical and horizontal scroll bars belong to different elements

Status: NEW

(Core :: Layout, enhancement, P3)

Description

[Yuri Khan]

User Agent: Mozilla/5.0 (X11; Ubuntu; Linux x86_64; rv:58.0) Gecko/20100101 Firefox/58.0
Build ID: 20180112141218

Steps to reproduce:

0. In Preferences | General | Browsing, enable [x] Use autoscrolling.
1. Open this fiddle: https://jsfiddle.net/yurikhan/nw25dd4f/3/
1a. Observe the hierarchy: body > p + pre. Observe that body has a vertical scroll bar while pre has a horizontal scroll bar.
2. In the result pane, middle-click in the first paragraph. Observe that the body element scrolls vertically.
3. In the result pane, middle-click in the preformatted text of the second paragraph.


Actual results:

The preformatted element horizontally. It is not possible to scroll the page body vertically by starting the autoscroll operation at a point within the preformatted text.


Expected results:

Desired result: display a four-way autoscroll cursor; apply the horizontal component of the scrolling to the pre and the vertical component to the body.

In the general case, apply the vertical and horizontal components to the innermost vertically scrollable and innermost horizontally scrollable elements containing the starting point.

(Bonus points if, in case of nested vertically scrollable containers, after scrolling to the end of the innermost one, scrolling continues with the outer one.)


In the real life use case that led me to file this bug, the inner element is a file in a code review system, annotated with line numbers and author name. It is often wide enough to cause horizontal scrolling. The file is also typically long enough to need vertical scrolling, but there is almost nowhere to middle-click to start vertical autoscrolling.

Comment 1

[Yuri Khan]

(typo: Actual results: The preformatted element +scrolls+ horizontally.)

Comment 2

[Jet Villegas (inactive)]

[ Triage 2017/02/20: P3 ]

Comment 3

[Alice0775 White]

Chrome does. But, Firefox and Edge don't.