1491220 - Mousewheel scroll speed should not change based on zoom level

Status: UNCONFIRMED

(Core :: Panning and Zooming, defect, P3)

Description

[nyanpasu64]

User Agent: Mozilla/5.0 (X11; Linux x86_64; rv:64.0) Gecko/20100101 Firefox/64.0
Build ID: 20180913100107

Steps to reproduce:

Possibly disable View/Zoom/Zoom Text Only.

Zoom in or out of a page (as far as possible for maximum effect)
- When browsing the web, I often zoom due to text I find uncomfortably large or small.

Scroll up or down.


Actual results:

The scroll distance is approximately proportional to zoom level (scrolls a fixed number of CSS pixels through the page). On pages with large text, if I zoom to shrink, every scroll wheel click covers less lines than normal pages (with or without zooming out).


Expected results:

The scroll distance is independent of zoom level, and corresponds to a specific distance on screen. (I usually zoom the page until the font size is approximately 10-14pt, so the on-screen distance corresponds to a nearly consistent number of lines).

https://bugzilla.mozilla.org/show_bug.cgi?id=844653 requested this behavior for touchpad scrolling, which hasn't happened yet.

Comment 1

[Botond Ballo [:botond]]

The intention is for mousewheel to scroll by a fixed number of lines of text (unless configured, usually via OS settings, to scroll by a fixed number of pixels or a whole page, instead). The amount of pixels that translates to will naturally vary with the zoom level.

Of course, scrollable content can contain a variety of text of different sizes, and so figuring out what text size to base "the height of a line of text" on is a heuristic. If there are pages where you find this heuristic is performing poorly (that is, a mousewheel event is scrolling significantly fewer or more lines of text than a more typical, average-font-size page), I would suggest filing bugs about one or more specific pages; perhaps the heuristic can be improved.

Comment 2

[Botond Ballo [:botond]]

To answer the specific request of having mousewheel scroll by a fixed number of screen pixels: I doubt that's going to be something we do by default, or even something we add an about:preferences option for. I would probably accept a patch to add an about:config option to do that.

However, it seems what you're really after is scrolling by a fixed number of lines consistently, so if we fix that, there should be no need for the screen-pixel option.