982819 - [HiDPI] Ctrl mousewheel won't zoom out to device pixels on 144DPI

Status: NEW

(Firefox :: General, defect)

Description

[Greg Edwards]

Attachment: Simple testcase that echoes window.devicePixelRatio back to you

User Agent: Mozilla/5.0 (Windows NT 6.3; WOW64; rv:27.0) Gecko/20100101 Firefox/27.0 (Beta/Release)
Build ID: 20140212131424

Steps to reproduce:

Set Windows to 150% scale (144DPI).
Open the attached testcase.
Attempt to get it to tell you that your zoom level is 1.


Actual results:

You can't get it to reach exactly 1. It skips between 1.0526316165924072... and 0.89552241563797.
Even with NoSquint, the closest I can get is 0.96x


Expected results:

I should be able to get it to go to exactly 1x.

Device pixel zoom level is the most common configuration and being able to test websites at it is essential for any web developer. Furthermore, some website have bugs if they're not displayed at device pixel zoom, so it becomes impossible to work around them if you can't actually set your browser to it.

The zoom level stops are all at 10% increments, but device pixel zoom is 66.67% when Windows's DPI is at 150%. Perhaps the simplest fix is to add 66.67% to the list of valid zoom levels. You could also show zoom levels in device pixels (like IE) but I understand that approach is unsustainable as monitor pixel densities rise.

Comment 1

[Greg Edwards]

Of note is that you actually can set device pixel zoom with any of Windows's other DPI settings, since the multiplier is always one of the built-in stops. (100%, 80%, or 50%)

Comment 2

[Karl Tomlinson (:karlt)]

This WFM when using ^= and ^- and UI zoom.

The 0.67 should be getting rounded to 2/3, and I don't think anything has changed recently there.
http://hg.mozilla.org/mozilla-central/annotate/ae27ae77e32f/modules/libpref/init/all.js#l3704

So I assume this bug is about using the mouse wheel with ctrl.
The code for that should probably also respect the pref, like the visible UI features.
http://dxr.mozilla.org/mozilla-central/source/dom/events/EventStateManager.cpp#1989
http://hg.mozilla.org/mozilla-central/annotate/ae27ae77e32f/toolkit/content/viewZoomOverlay.js#l66

Comment 3

[Greg Edwards]

By golly, you're right! (But I also had to disable the NoSquint addon! NoSquint makes ctrl++/- behave just like the buggy mousewheel shortcut. I'll file a bug with them.)