677900 - allow multiple faces sharing the same style attributes within a font family

Status: RESOLVED WORKSFORME

(Core :: Graphics, defect)

Description

[Jonathan Kew [:jfkthame]]

Attachment: patch, support multiple font entries with the same style attributes within a family

Currently, our code assumes that a given set of CSS font-* properties (weight, width, style) will uniquely identify a single face within a font family. In particular, we have gfxFontFamily::FindFontForStyle(), which returns a single face from the family.

While this holds true in most common cases, there are several scenarios where a family may have several faces that match a given set of CSS properties. Generalizing the font-matching code so that we have gfxFontFamily::FindFontsForStyle() returning an array of matching faces will facilitate fixing a number of issues:

- bug 465414 (should do glyph fallback across multiple @font-face rules defining the same font)
- bug 465450 (a specific bug report that arises because of the above)
- bug 475891 (unicode-range support, which is an enhancement of the above)
- bug 469656 (support the OpenType optical size feature, if present)
- bug 636042 (Samsung problem due to presence of subsetted fonts - worked around by using a whitelist of "preferred" standard fonts, but this would mitigate the issue in a general way)

The attached patch provides support for multiple faces having the same style properties. This was tested on tryserver and does not appear to significantly impact performance; some platforms did show a small (<1%) regression, but others showed a comparable _improvement_.

Comment 1

[John Daggett (:jtd)]

Comment on attachment 552074 [details] [diff] [review]
patch, support multiple font entries with the same style attributes within a family

I'm minus'ing this because in the general case, having more than one
font map to the same set of style characteristics is a bug.  There's
no great benefit to supporting this in the general case.

Without support for the general case, this boils down to supporting
unicode-range.  I'd be fine if the patch only applies to @font-face
rule defined faces, as a part of supporting unicode-range.

Comment 2

[Eric A. Meyer]

So is support for 'unicode-range' happening here, or in bug 475891?

Comment 3

[John Daggett (:jtd)]

(In reply to Eric A. Meyer from comment #2)
> So is support for 'unicode-range' happening here, or in bug 475891?

In bug 475891.

Comment 4

[Eric A. Meyer]

Thanks, John!

Comment 5

[Jonathan Kew [:jfkthame]]

Something much like this happened as part of unicode-range support, to the point where I think we can close this as WFM.