reftests gfx/layers/apz/reftests/async-scrollbar-1-v.html show a discrepancy in the scroll position on android since freetype 2.8

NEW
Unassigned

Status

()

Core
Panning and Zooming
P3
normal
3 months ago
2 months ago

People

(Reporter: jfkthame, Unassigned)

Tracking

57 Branch
All
Android
Points:
---

Firefox Tracking Flags

(firefox55 unaffected, firefox56 unaffected, firefox57 fix-optional)

Details

(Whiteboard: [gfx-noted])

(Reporter)

Description

3 months ago
See bug 1364714 comment 42. The freetype 2.8 update causes a (small) change in the font metrics returned for our default sans-serif font on Android, and for some reason this appears to be causing a discrepancy on these reftests.

It's not immediately clear to me why font metrics should be important here, though, as the tests don't seem to use any text, just a div with a (huge) specified height.
Also for the record, when adding those tests I recall running into a lot of rounding errors and the numbers that I used for the scrollbar position and size of the div were chosen precisely to avoid much of the rounding error. It's quite likely that the freetype update just perturbed enough stuff to make those particular numbers now trigger a different rounding error so the scrollbar position is off by one. We can probably just adjust the numbers a little to bring the scrollbar position back in alignment.
OS: Unspecified → Android
Priority: -- → P3
Hardware: Unspecified → All
Whiteboard: [gfx-noted]
Version: unspecified → 57 Branch
status-firefox55: --- → unaffected
status-firefox56: --- → unaffected
status-firefox57: --- → fix-optional
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