1386777 - Mouse position relative to autoscroll indicator is not interpreted correctly (possibly due to devicePixelRatio)

Status: VERIFIED FIXED

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

Description

[Kartikaya Gupta (email:[e-mail])]

I just tried the APZ autoscroll on my Surface tablet, and it looks like the mouse position is not being interpeted properly. The device has a window.devicePixelRatio of 1.5 which I suspect is not handled correctly.

If I middle-click to start autoscroll near the bottom of the window, the content immediately autoscrolls super-fast to the bottom of the page. If I middle-click near the top of the content area, it still autoscrolls down to the bottom, but less fast. In all cases I have to my mouse cursor sigificantly farther up than the indicator in order to get it scroll upwards, and if I keep the mouse near the indicator or even just above it, it scrolls downwards. ("Above" and "below" here refer to y-axis).

Comment 1

[Botond Ballo [:botond]]

(In reply to Kartikaya Gupta (email:[e-mail]) from comment #0)
> If I middle-click to start autoscroll near the bottom of the window, the
> content immediately autoscrolls super-fast to the bottom of the page. If I
> middle-click near the top of the content area, it still autoscrolls down to
> the bottom, but less fast. In all cases I have to my mouse cursor
> sigificantly farther up than the indicator in order to get it scroll
> upwards, and if I keep the mouse near the indicator or even just above it,
> it scrolls downwards.

That matches the symptoms I saw with full zoom > 100% before I fixed the patch to handle full zoom correctly. I guess that fix did not correctly handle other sources of a device pixel ratio.

Comment 2

[Botond Ballo [:botond]]

I can reproduce this on a regular desktop machine by setting the pref layout.css.devPixelsPerPx to 1.5. Will investigate.

Comment 3

[Botond Ballo [:botond]]

Attachment: Bug 1386777 - Interpret autoscroll anchor coordinates correctly when there is a device scale.

Review commit: https://reviewboard.mozilla.org/r/164148/diff/#index_header
See other reviews: https://reviewboard.mozilla.org/r/164148/

Comment 4

[Botond Ballo [:botond]]

This patch fixes the issue for me when layout.css.devPixelPerPx is modified.

Kats, when a get you chance, could you try the patch on your tablet as well?

Comment 5

[Kartikaya Gupta (email:[e-mail])]

Yup, this patch fixes the issue for me.

Comment 6

[Botond Ballo [:botond]]

Great, thanks for testing!

Comment 7

[Kartikaya Gupta (email:[e-mail])]

Comment on attachment 8893151 [details]
Bug 1386777 - Interpret autoscroll anchor coordinates correctly when there is a device scale.

https://reviewboard.mozilla.org/r/164148/#review169822

Comment 9

[Pulsebot]

Pushed by [e-mail]:
https://hg.mozilla.org/integration/autoland/rev/3af71fa1f3dd
Interpret autoscroll anchor coordinates correctly when there is a device scale. r=kats

Comment 10

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

https://hg.mozilla.org/mozilla-central/rev/3af71fa1f3dd

Comment 11

[Botond Ballo [:botond]]

Comment on attachment 8893151 [details]
Bug 1386777 - Interpret autoscroll anchor coordinates correctly when there is a device scale.

Approval Request Comment
[Feature/Bug causing the regression]:
  Bug 1105109

[User impact if declined]:
  Users who would like to try out APZ autoscrolling in 56 Beta
  on devices with a pixel density > 1 will not be able to.

[Is this code covered by automated tests?]:
  Not that I'm aware of

[Has the fix been verified in Nightly?]:
  Yes

[Needs manual test from QE? If yes, steps to reproduce]: 
  No

[List of other uplifts needed for the feature/fix]:
  None

[Is the change risky?]:
  Very low risk

[Why is the change risky/not risky?]:
  It's a small fix to a codepath that's prefed off by default.

[String changes made/needed]:
  None

Comment 12

[Aki Sasaki (not active)]

https://hg.mozilla.org/projects/date/rev/3af71fa1f3dd1cf6083f84612c2fb99ed765d2fb
Bug 1386777 - Interpret autoscroll anchor coordinates correctly when there is a device scale. r=kats

Comment 13

[Liz Henry (:lizzard) (relman/hg->git project)]

Comment on attachment 8893151 [details]
Bug 1386777 - Interpret autoscroll anchor coordinates correctly when there is a device scale.

Another tweak useful for APZ testing in beta 56. This should land in beta 2.

Comment 14

[Ryan VanderMeulen [:RyanVM]]

https://hg.mozilla.org/releases/mozilla-beta/rev/de3698e225ce

Comment 15

[Petruta Horea [:phorea], Desktop Test Engineering]

Verified as fixed using Firefox 56.0 beta 2 and latest Nightly 57.0a1 2017-08-11.