1593813 - The length unit Q miscalculated

Status: NEW

(Core :: CSS Parsing and Computation, defect, P3)

Description

[hao]

Attachment: line-height-interpolation.html

User Agent: Mozilla/5.0 (X11; Linux x86_64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/78.0.3904.70 Safari/537.36

Steps to reproduce:

Run the attached test with Firefox nightly build.

Actual results:

property <line-height> from [4q] to [19q] (15q unit) got 17.97 px.

Expected results:

It should be 17.95px. (https://developer.mozilla.org/en-US/docs/Web/CSS/length)

Comment 1

[Emilio Cobos Álvarez (:emilio)]

This is probably just a float precision issue of sorts, combined with the fact that line-height requires conversion to app-units...

Comment 2

[Mats Palmgren (inactive)]

Hmm, isn't this testcase just bogus since it makes assumptions about the absence of rounding errors in a resolved length value? I don't think there are any guaranties in CSS about that for properties that report actual layout values like line-height, width, height etc

Comment 3

[Emilio Cobos Álvarez (:emilio)]

Yeah, though in this case we can represent the 15q value exactly with app-units, so there's a precision error somewhere in the interpolation code that may be worth at least diagnosing (even if it's WONTFIX).