1611610 - synthetic-bold effect should not increase the advance of zero-width glyphs

Status: RESOLVED FIXED

(Core :: Layout: Text and Fonts, defect, P3)

Description

[Jonathan Kew [:jfkthame]]

Generally, when synthetic bold is applied (because font-weight calls for bold, but no actual bold face is available for the font family in use), glyph advances are increased to account for the "fattening" of the glyphs.

However, for zero-width glyphs we shouldn't do this; if a glyph has an advance width of zero, it is expected that it will not result in any extra space between its neighbors, and we should maintain that behavior even when synthetic bold is involved.

Comment 1

[Jonathan Kew [:jfkthame]]

(Note that this is specific to platforms where we use gecko's built-in "synthetic bold by multi-striking" implementation; where we're using a platform font backend's synthetic bold (such as DirectWrite "simulations") we simply use whatever glyph advances it gives us.)

Comment 2

[Jonathan Kew [:jfkthame]]

Attachment: Bug 1611610 - Don't increase glyph advance for synthetic bold if the glyph is zero-width. r=lsalzman

Comment 3

[Jonathan Kew [:jfkthame]]

Attachment: Bug 1611610 - Add reftest for effect of synthetic bold on metrics of zero-width glyph. r=lsalzman

Depends on D61065

Comment 4

[Jonathan Kew [:jfkthame]]

The above reftest fails on macOS without the patch, due to this bug; I think this may currently be our only affected platform. (Checking on tryserver whether the test passes as expected everywhere else.)

Comment 5

[Pulsebot]

Pushed by [e-mail]:
https://hg.mozilla.org/integration/autoland/rev/ed3330607ac3
Don't increase glyph advance for synthetic bold if the glyph is zero-width. r=lsalzman
https://hg.mozilla.org/integration/autoland/rev/66c0610ae7ce
Add reftest for effect of synthetic bold on metrics of zero-width glyph. r=lsalzman

Comment 6

[Andreea Pavel [:apavel]]

https://hg.mozilla.org/mozilla-central/rev/ed3330607ac3
https://hg.mozilla.org/mozilla-central/rev/66c0610ae7ce