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Suspected endless loop in autohinting Shaper coverage computation with Poppins Semibold #1295

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drott opened this issue Dec 20, 2024 · 4 comments · May be fixed by #1296
Open

Suspected endless loop in autohinting Shaper coverage computation with Poppins Semibold #1295

drott opened this issue Dec 20, 2024 · 4 comments · May be fixed by #1296

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@drott
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drott commented Dec 20, 2024 •
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In Chrome content_shell and https://rtsh.es/test/poppins.html the content tab starts to hang.
Running this and content_shell with gdb
$ gdb --args out/gnrelease/content_shell --single-process https://rtsh.es/test/poppins.html
Then stopping and running
thread apply all backtrace

reveals the stack trace at which this is hanging:

[#65 repeats]
#65 0x00007ffff5913703 in skrifa::outline::autohint::shape::GsubHandler::process_lookup::h05a71b4249d913f6 () at /usr/local/google/home/drott/dev/blink/src/out/gnrelease/libskia.so
#66 0x00007ffff5910d39 in skrifa::outline::autohint::shape::Shaper::compute_coverage::h8b6af0d2971cd068 () at /usr/local/google/home/drott/dev/blink/src/out/gnrelease/libskia.so
#67 0x00007ffff58fe6fd in skrifa::outline::autohint::style::GlyphStyleMap::new::he7232822c79b7d06 () at /usr/local/google/home/drott/dev/blink/src/out/gnrelease/libskia.so
#68 0x00007ffff590021b in skrifa::outline::autohint::instance::GlyphStyles::new::h8993ddbc473295b4 () at /usr/local/google/home/drott/dev/blink/src/out/gnrelease/libskia.so
#69 0x00007ffff5900407 in skrifa::outline::autohint::instance::Instance::new::h1fd5544fce0fc93c () at /usr/local/google/home/drott/dev/blink/src/out/gnrelease/libskia.so
#70 0x00007ffff587e861 in skrifa::outline::hint::HintingInstance::reconfigure::hff00a995aaa3c43c () at /usr/local/google/home/drott/dev/blink/src/out/gnrelease/libskia.so
#71 0x00007ffff587efe2 in skrifa::outline::hint::HintingInstance::new::h8760a010858fb68a () at /usr/local/google/home/drott/dev/blink/src/out/gnrelease/libskia.so
#72 0x00007ffff5866eaf in skia_cbridge_urust_uside::make_hinting_instance::h8f1b0d2f10919329 () at /usr/local/google/home/drott/dev/blink/src/out/gnrelease/libskia.so
#73 0x00007ffff57b1c94 in fontations_ffi::make_hinting_instance(fontations_ffi::BridgeOutlineCollection const&, float, fontations_ffi::BridgeNormalizedCoords const&, bool, bool, bool, bool) () at /usr/local/google/home/drott/dev/blink/src/out/gnrelease/libskia.so
#74 0x00007ffff53492d7 in SkFontationsScalerContext::SkFontationsScalerContext(sk_sp<SkTypeface_Fontations>, SkScalerContextEffects const&, SkDescriptor const*, sk_sp<SkTypeface>) () at /usr/local/google/home/drott/dev/blink/src/out/gnrelease/libskia.so
@drott
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drott commented Dec 20, 2024

Repro snippet example: https://gist.github.com/drott/358588887648cefdf845f7a33451f0c2

@drott
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drott commented Dec 20, 2024

Does seem to occur with Poppins 4.003 from MS:
https://puzmo.blob.core.windows.net/assets/fonts/Poppins-SemiBold.ttf
but not with 4.004(b4) from Google Fonts.

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drott commented Dec 20, 2024

Does not repro with https://github.com/itfoundry/Poppins/releases/tag/v4.003 and file Poppins-SemiBold.ttf from that archive.

@drott drott mentioned this issue Dec 20, 2024
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@dfrg
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dfrg commented Dec 20, 2024

Does seem to occur with Poppins 4.003 from MS: https://puzmo.blob.core.windows.net/assets/fonts/Poppins-SemiBold.ttf but not with 4.004(b4) from Google Fonts.

In this font, lookup 27 (from abvs feature) is a contextual lookup with two subtables that both chain to lookup 0 which is another contextual lookup with four subtables that all cycle.

dfrg added a commit that referenced this issue Dec 20, 2024
@dfrg
[skrifa] autohint: cycle detection for GSUB lookups
17690f2 
Adds a stack to detect cycles in GSUB lookups while computing shaper coverage for autohinting.

Fixes #1295
@dfrg dfrg linked a pull request Dec 20, 2024 that will close this issue
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[skrifa] autohint: cycle detection for GSUB lookups googlefonts/fontations
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@dfrg @drott