Lazy load fonts in a FontGroup
The first commit message explains this so I'll just copy it here:
---
This is a step towards fixing #17267. To fix that, we need to be able to
try various different fallback fonts in turn, which would become
unweildy with the prior eager-loading strategy.
Prior to this change, FontGroup loaded up all Font instances, including
the fallback font, before any of them were checked for the presence of
the glyphs we're trying to render.
So for the following CSS:
font-family: Helvetica, Arial;
The FontGroup would contain a Font instance for Helvetica, and a Font
instance for Arial, and a Font instance for the fallback font.
It may be that Helvetica contains glyphs for every character in the
document, and therefore Arial and the fallback font are not needed at
all.
This change makes the strategy lazy, so that we'll only create a Font
for Arial if we cannot find a glyph within Helvetica. I've also
substantially refactored the existing code in the process and added
some documentation along the way.
---
I've added some tests in the second commit, but it required quite a bit of gymnastics to make it possible to write such a test. I'm not sure if the added complexity to the production code is worth it?
On the other hand, having this infrastructure in place may be useful for testing future changes in this area, and also possibly brings us a step closer to extracting a library as discussed in #4901. (What I mean by that is: it reduces coupling between `FontCacheThread` and `FontContext` -- the latter would have a place in such a library, the former wouldn't.)
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This is a step towards fixing #17267. To fix that, we need to be able to
try various different fallback fonts in turn, which would become
unweildy with the prior eager-loading strategy.
Prior to this change, FontGroup loaded up all Font instances, including
the fallback font, before any of them were checked for the presence of
the glyphs we're trying to render.
So for the following CSS:
font-family: Helvetica, Arial;
The FontGroup would contain a Font instance for Helvetica, and a Font
instance for Arial, and a Font instance for the fallback font.
It may be that Helvetica contains glyphs for every character in the
document, and therefore Arial and the fallback font are not needed at
all.
This change makes the strategy lazy, so that we'll only create a Font
for Arial if we cannot find a glyph within Helvetica. I've also
substantially refactored the existing code in the process and added
some documentation along the way.
Issue #17321. Under Linux, using "font-family: sans-serif" previously
caused Servo to select the "UltraLight" face (of DejaVu Sans). There
were two reasons for this:
1. Font weight was only retrieved from the OS/2 table for bold faces.
This neglected to retrieve the weight information for "lighter than
normal" weight faces. This meant that the UltraLight face appeared as
normal weight, and was selected.
2. Retrieval of font stretch information from the OS/2 table was not
implemented at all.
Instead use C-level malloc()/free() so that the size doesn’t need
to be known during deallocation, since FreeType doesn’t provide it.
Hopefully fixes https://github.com/servo/servo/issues/19058
Servo currently uses `heapsize`, but Stylo/Gecko use `malloc_size_of`.
`malloc_size_of` is better -- it handles various cases that `heapsize` does not
-- so this patch changes Servo to use `malloc_size_of`.
This patch makes the following changes to the `malloc_size_of` crate.
- Adds `MallocSizeOf` trait implementations for numerous types, some built-in
(e.g. `VecDeque`), some external and Servo-only (e.g. `string_cache`).
- Makes `enclosing_size_of_op` optional, because vanilla jemalloc doesn't
support that operation.
- For `HashSet`/`HashMap`, falls back to a computed estimate when
`enclosing_size_of_op` isn't available.
- Adds an extern "C" `malloc_size_of` function that does the actual heap
measurement; this is based on the same functions from the `heapsize` crate.
This patch makes the following changes elsewhere.
- Converts all the uses of `heapsize` to instead use `malloc_size_of`.
- Disables the "heapsize"/"heap_size" feature for the external crates that
provide it.
- Removes the `HeapSizeOf` implementation from `hashglobe`.
- Adds `ignore` annotations to a few `Rc`/`Arc`, because `malloc_size_of`
doesn't derive those types, unlike `heapsize`.
Improve font layout in Linux / Freetype platforms.
This patch contains two small changes:
* Fix the font size calculation that is passed to Freetype. This
now matches exactly how Webrender and Gecko calculate font size
to pass to layout.
* Enable light hinting by default for fonts when using Freetype.
We should make this configurable in the future, but this is a
better default than no hinting (and matches what most Linux
distros default to).
These two changes (along with the pending WR update) fix a lot
of the font layout issues on Linux. There is still at least one
remaining issue with hidpi displays on Linux that will be fixed
in a follow up patch.
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This patch contains two small changes:
* Fix the font size calculation that is passed to Freetype. This
now matches exactly how Webrender and Gecko calculate font size
to pass to layout.
* Enable light hinting by default for fonts when using Freetype.
We should make this configurable in the future, but this is a
better default than no hinting (and matches what most Linux
distros default to).
These two changes (along with the pending WR update) fix a lot
of the font layout issues on Linux. There is still at least one
remaining issue with hidpi displays on Linux that will be fixed
in a follow up patch.
