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fonts: Remove the per-FontGroup cached fallback font (#35705)

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Instead of keeping a per-FontGroup cache of the previously used fallback
font, cache this value in the caller of `FontGroup::find_by_codepoint`.
The problem with caching this value in the `FontGroup` is that it can
make one layout different from the next.

Still, it is important to cache the value somewhere so that, for
instance, Chinese character don't have to continuously walk through the
entire fallback list when laying out. The heuristic here is to try to
last used font first if the `Script`s match. At the very least this
should make one layout consistent with the next.

Fixes #35704.
Fixes #35697.
Fixes #35689.
Fixes #35679.

Signed-off-by: Martin Robinson <mrobinson@igalia.com>
This commit is contained in:
Martin Robinson 2025-02-28 15:33:21 +01:00 • committed by GitHub
parent 06d4272462
commit f949d2adc8
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13 changed files with 43 additions and 38 deletions
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13
components/fonts/font.rs
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@ -568,8 +568,6 @@ pub type FontRef = Arc<Font>;
pub struct FontGroup {
descriptor: FontDescriptor,
families: SmallVec<[FontGroupFamily; 8]>,
#[ignore_malloc_size_of = "This measured in the FontContext font cache."]
last_matching_fallback: Option<FontRef>,
}
impl FontGroup {
@ -584,7 +582,6 @@ impl FontGroup {
FontGroup {
descriptor,
families,
last_matching_fallback: None,
}
}
@ -597,6 +594,7 @@ impl FontGroup {
font_context: &FontContext,
codepoint: char,
next_codepoint: Option<char>,
first_fallback: Option<FontRef>,
) -> Option<FontRef> {
// Tab characters are converted into spaces when rendering.
// TODO: We should not render a tab character. Instead they should be converted into tab stops
@ -642,11 +640,11 @@ impl FontGroup {
return font_or_synthesized_small_caps(font);
}
if let Some(ref last_matching_fallback) = self.last_matching_fallback {
if char_in_template(last_matching_fallback.template.clone()) &&
font_has_glyph_and_presentation(last_matching_fallback)
if let Some(ref first_fallback) = first_fallback {
if char_in_template(first_fallback.template.clone()) &&
font_has_glyph_and_presentation(first_fallback)
{
return font_or_synthesized_small_caps(last_matching_fallback.clone());
return font_or_synthesized_small_caps(first_fallback.clone());
}
}
@ -656,7 +654,6 @@ impl FontGroup {
char_in_template,
font_has_glyph_and_presentation,
) {
self.last_matching_fallback = Some(font.clone());
return font_or_synthesized_small_caps(font);
}