Instead of using a simple `Atom` to identify a local font, use a data
structure. This allows us to carry more information necessary to
identify a local font (such as a path on MacOS). We need this for the
new version of WebRender, as fonts on MacOS now require a path.
This has a lot of benefits:
1. We can avoid loading fonts without paths on MacOS, which should
avoid a lot of problems with flakiness and ensure we always load the
same font for a given identifier.
2. This clarifies the difference between web fonts and local fonts,
though there is more work to do here.
3. This avoid a *lot* of font shenanigans, such as trying to work
backwards from the name of the font to the path of the font we
actually matched. In general, we can remove a lot of code trying to
accomplish these shenanigans.
4. Getting the font bytes always returns an `Arc` now avoiding an extra
full font copy in the case of Canvas.
Prior to this change, if none of the fonts specified in CSS contained a
glyph for a codepoint, we tried only one fallback font. If that font
didn't contain the glyph, we'd give up.
With this change, we try multiple fonts in turn. The font names we try
differ across each platform, and based on the codepoint we're trying to
match. The current implementation is heavily inspired by the analogous
code in Gecko, but I've used to ucd lib to make it more readable,
whereas Gecko matches raw unicode ranges.
This fixes some of the issues reported in #17267, although colour emoji
support is not implemented.
== Notes on changes to WPT metadata ==
=== css/css-text/i18n/css3-text-line-break-opclns-* ===
A bunch of these have started failing on macos when they previously
passed.
These tests check that the browser automatically inserts line breaks
near certain characters that are classified as "opening and closing
punctuation". The idea is that if we have e.g. an opening parenthesis,
it does not make sense for it to appear at the end of a line box; it
should "stick" to the next character and go into the next line box.
Before this change, a lot of these codepoints rendered as a missing
glyph on Mac and Linux. In some cases, that meant that the test was
passing.
After this change, a bunch of these codepoints are now rendering glyphs
on Mac (but not Linux). In some cases, the test should continue to pass
where it previously did when rendering with the missing glyph.
However, it seems this has also exposed a layout bug. The "ref" div in
these tests contains a <br> element, and it seems that this, combined
with these punctuation characters, makes the spacing between glyphs ever
so slightly different to the "test" div. (Speculation: might be
something to do with shaping?)
Therefore I've had to mark a bunch of these tests failing on mac.
=== css/css-text/i18n/css3-text-line-break-baspglwj-* ===
Some of these previously passed on Mac due to a missing glyph. Now that
we're rendering the correct glyph, they are failing.
=== css/css-text/word-break/word-break-normal-bo-000.html ===
The characters now render correctly on Mac, and the test is passing. But
we do not find a suitable fallback font on Linux, so it is still failing
on that platform.
=== css/css-text/word-break/word-break-break-all-007.html ===
This was previously passing on Mac, but only because missing character
glyphs were rendered. Now that a fallback font is able to be found, it
(correctly) fails.
=== mozilla/tests/css/font_fallback_* ===
These are new tests added in this commit. 01 and 02 are marked failing
on Linux because the builders don't have the appropriate fonts installed
(that will be a follow-up).
Fix build errors from rebase
FontTemplateDescriptor can no longer just derive(Hash). We need to
implement it on each component part, because the components now
generally wrap floats, which do not impl Hash because of NaN. However in
this case we know that we won't have a NaN, so it is safe to manually
impl Hash.
The freetype hinting only works on integer pixel sizes. For this
reason, the advance width metrics for a font of size 12.99 are
the same as the advance metrics for a font of size 12.0. This
results in small fonts appearing to overlap slightly, which is
particularly noticeable on parts of Wikipedia. Round the font
size up to a pixel boundary inside the freetype system.
Also fetch the system default fonts for the generic font families
rather than hard coding them.
These two changes make the font rendering on Linux very close
to the Firefox font rendering on Wikipedia.
