883997 - FT2 font backend is inconsistent in whether ascent/descent metrics are rounded to pixels

Status: RESOLVED FIXED

(Core :: Graphics: Text, defect)

Description

[Jonathan Kew [:jfkthame]]

Attachment: patch, consistently use pixel-rounded values for maxAscent/Descent in the FT2 font metrics

Moving this to a new bug from bug 877203 comment 55. FreeType normally gives us pixel-rounded metrics for ascent and descent, but then in some cases (depending how the true "typographic" values compare to the rounded ones) we sometimes end up setting maxAscent or maxDescent to a fractionally larger, unrounded value.

AIUI, this leads to an unexpected discrepancy between the line height calculated for an entirely empty line, based on the rounded em-height and leading values, and the height for a line that contains frames, which make use of the maxAscent/Descent values.

The patch here makes us consistently use pixel-rounded metrics for these fields, and resolves all the line-height-related reftest failures that were showing up in bug 877203.

Comment 1

[Jonathan Kew [:jfkthame]]

https://hg.mozilla.org/integration/mozilla-inbound/rev/1bd6b04a535f

Comment 2

[Jonathan Kew [:jfkthame]]

https://hg.mozilla.org/mozilla-central/rev/1bd6b04a535f

Argh - the patch still had the old bug number (877203) in its commit message, so that's what ended up in m-c. Sorry.