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Bug 1787603 - Only pass content lang to fontconfig for CJK & Arabic scripts, to avoid performance quagmire on pages like wikipedia.org. r=jwatt

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This in effect reverts part of bug 1756400, so that we only do the full
per-language fontconfig substitution processing for locales that use
CJK or Arabic script. These are the locales where it is likely that
there may be custom per-language/locale font preferences that need to
be respected.

(In theory fontconfig could be set up with per-language rules even for
distinctions like 'en-US' vs 'en-GB', or 'en' vs 'fr' vs 'de', etc.,
and we will no longer respect these. But it is almost vanishingly unlikely
that separate font mappings for such distinctions will really be needed,
and the cost of doing all the lookups separately for every lang tag,
even within simple writing systems like Latin, is excessive.)

No automated tests, as this is heavily dependent on the system configuration.

Differential Revision: https://phabricator.services.mozilla.com/D162304
This commit is contained in:
Jonathan Kew 2022-11-21 15:01:24 +00:00
parent e447486663
commit 916053d932
1 changed files with 49 additions and 10 deletions
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59
gfx/thebes/gfxFcPlatformFontList.cpp
View File

@ -29,6 +29,7 @@
#include "nsXULAppAPI.h"
#include "SharedFontList-impl.h"
#include "StandardFonts-linux.inc"
#include "mozilla/intl/Locale.h"
#include "mozilla/gfx/HelpersCairo.h"
@ -60,6 +61,7 @@
using namespace mozilla;
using namespace mozilla::gfx;
using namespace mozilla::unicode;
using namespace mozilla::intl;
#ifndef FC_POSTSCRIPT_NAME
# define FC_POSTSCRIPT_NAME "postscriptname" /* String */
@ -2087,6 +2089,12 @@ gfxFontEntry* gfxFcPlatformFontList::MakePlatformFont(
std::move(face));
}
static bool UseCustomFontconfigLookupsForLocale(const Locale& aLocale) {
return aLocale.Script().EqualTo("Hans") || aLocale.Script().EqualTo("Hant") ||
aLocale.Script().EqualTo("Jpan") || aLocale.Script().EqualTo("Kore") ||
aLocale.Script().EqualTo("Arab");
}
bool gfxFcPlatformFontList::FindAndAddFamiliesLocked(
nsPresContext* aPresContext, StyleGenericFontFamily aGeneric,
const nsACString& aFamily, nsTArray<FamilyAndGeneric>* aOutput,
@ -2136,14 +2144,28 @@ bool gfxFcPlatformFontList::FindAndAddFamiliesLocked(
// Nimbus Sans L as alternatives for Helvetica.
// Because the FcConfigSubstitute call is quite expensive, we cache the
// actual font families found via this process. We include the language (if
// any) as part of the cache key because fontconfig may have lang-specific
// rules that specify different substitutions.
// actual font families found via this process.
nsAutoCString lang;
GetSampleLangForGroup(aLanguage, lang);
nsAutoCString cacheKey(lang);
ToLowerCase(cacheKey);
cacheKey.Append(':');
ToLowerCase(lang);
nsAutoCString cacheKey;
// For languages that use CJK or Arabic script, we include the language as
// part of the cache key because fontconfig may have lang-specific rules that
// specify different substitutions. (In theory, this could apply to *any*
// language, but it's highly unlikely to matter for non-CJK/Arabic scripts,
// and it gets really expensive to do separate lookups for 300+ distinct lang
// tags e.g. on wikipedia.org, when they all end up mapping to the same font
// list.)
Locale locale;
if (LocaleParser::TryParse(lang, locale).isOk() &&
locale.AddLikelySubtags().isOk()) {
if (UseCustomFontconfigLookupsForLocale(locale)) {
cacheKey = lang;
cacheKey.Append(':');
}
}
cacheKey.Append(familyName);
if (const auto& cached = mFcSubstituteCache.Lookup(cacheKey)) {
if (cached->IsEmpty()) {
@ -2379,15 +2401,32 @@ gfxPlatformFontList::PrefFontList* gfxFcPlatformFontList::FindGenericFamilies(
GetSampleLangForGroup(aLanguage, fcLang);
ToLowerCase(fcLang);
nsAutoCString genericLang(aGeneric);
nsAutoCString cacheKey(aGeneric);
if (fcLang.Length() > 0) {
genericLang.Append('-');
cacheKey.Append('-');
// If the script is CJK or Arabic, we cache by lang so that different fonts
// various locales can be supported; but otherwise, we cache by script
// subtag, to avoid a proliferation of entries for Western & similar
// languages.
// In theory, this means we could fail to respect custom fontconfig rules
// for individual (non-CJK/Arab) languages that share the same script, but
// such setups are probably vanishingly rare.
Locale locale;
if (LocaleParser::TryParse(fcLang, locale).isOk() &&
locale.AddLikelySubtags().isOk()) {
if (UseCustomFontconfigLookupsForLocale(locale)) {
cacheKey.Append(fcLang);
} else {
cacheKey.Append(locale.Script().Span());
}
} else {
cacheKey.Append(fcLang);
}
}
genericLang.Append(fcLang);
// try to get the family from the cache
return mGenericMappings.WithEntryHandle(
genericLang, [&](auto&& entry) -> PrefFontList* {
cacheKey, [&](auto&& entry) -> PrefFontList* {
if (!entry) {
// if not found, ask fontconfig to pick the appropriate font
RefPtr<FcPattern> genericPattern = dont_AddRef(FcPatternCreate());