1487882 - PDF.js touchpad zoom too fast when MOZ_USE_XINPUT2 is enabled

Status: RESOLVED FIXED

(Firefox :: PDF Viewer, defect, P3)

Description

[cousteau]

Ingredients:
- Firefox 61
- Linux
- A laptop with a touchpad with scrolling gestures enabled (two-finger or side-scrolling)

Steps to reproduce:
1. Open Firefox with "pixel scrolling" enabled:
> env MOZ_USE_XINPUT2=1 firefox
2. Browse a PDF document
3. Hold Ctrl and scroll using the touchpad

Expected result:
- Zoom behaves like outside of PDF pages.  Not perfectly smooth pixel zoom (as in e.g. Evince) but at least it only jumps in increments of 10% every few pixels.
- Nice experience and controllable zoom.

Actual result:
- Zooming this way seems to change the zoom level by 10% for every PIXEL scrolled.
- Uncontrollable zoom and awful experience; it'll always end up jumping to either 10% or 250-ish%.
- Eventually giving up at zooming this way and cursing the day I decided to make MOZ_USE_XINPUT2=1 the default (which is nice otherwise).

Consequences:
- Low to no impact to the average user (for now).
- Although this is unlikely to cause trouble because MOZ_USE_XINPUT2 is disabled by default (I guess because of reasons such as this), it is a pity because that option is rather cool and should be implemented by default IMO, once every blocking bug (such as this one) is solved.

Comment 1

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

I think this should be fixed via bug 1392361, but I don't have a laptop with Linux to test this particular scenario. The next nightly should have the fix, can you please test to confirm?

Comment 2

[cousteau]

I can confirm that it is much more usable now; the zoom level is perfectly controllable with Ctrl + two finger scroll. Thanks!
Feel free to mark as fixed.