diff --git a/src/opentype/GSUBProcessor.js b/src/opentype/GSUBProcessor.js index f5672d5d..43a3e859 100644 --- a/src/opentype/GSUBProcessor.js +++ b/src/opentype/GSUBProcessor.js @@ -185,6 +185,25 @@ export default class GSUBProcessor extends OTProcessor { case 7: // Extension Substitution return this.applyLookup(table.lookupType, table.extension); + case 8: { // Reverse Chaining Contextual Single Substitution + let index = this.coverageIndex(table.coverage); + if (index === -1) { + return false; + } + + // Backtrack/lookahead contexts are checked against the current + // glyph in the buffer. The iteration order in applyLookups is + // reversed for Type 8 so lookahead always sees post-substitution + // glyphs (per OpenType spec) and backtrack sees pre-substitution. + if (this.coverageSequenceMatches(-table.backtrackGlyphCount, table.backtrackCoverage) + && this.coverageSequenceMatches(1, table.lookaheadCoverage)) { + this.glyphIterator.cur.id = table.substitute.get(index); + return true; + } + + return false; + } + default: throw new Error(`GSUB lookupType ${lookupType} is not supported`); } diff --git a/src/opentype/OTProcessor.js b/src/opentype/OTProcessor.js index 80d1ce69..53fa9bec 100644 --- a/src/opentype/OTProcessor.js +++ b/src/opentype/OTProcessor.js @@ -191,22 +191,25 @@ export default class OTProcessor { for (let { feature, lookup } of lookups) { this.currentFeature = feature; - this.glyphIterator.reset(lookup.flags); - while (this.glyphIterator.index < glyphs.length) { - if (!(feature in this.glyphIterator.cur.features)) { - this.glyphIterator.next(); - continue; - } - - for (let table of lookup.subTables) { - let res = this.applyLookup(lookup.lookupType, table); - if (res) { - break; + // GSUB Type 8 (Reverse Chaining Contextual Single Substitution) is + // applied in reverse direction per OpenType spec — process the run + // right-to-left so substitutions never feed back into the lookahead + // context of an earlier-in-text glyph. + let direction = lookup.lookupType === 8 ? -1 : 1; + let startIndex = direction === -1 ? glyphs.length - 1 : 0; + + this.glyphIterator.reset(lookup.flags, startIndex); + + while (this.glyphIterator.index >= 0 && this.glyphIterator.index < glyphs.length) { + if (feature in this.glyphIterator.cur.features) { + for (let table of lookup.subTables) { + if (this.applyLookup(lookup.lookupType, table)) { + break; + } } } - - this.glyphIterator.next(); + this.glyphIterator.move(direction); } } } diff --git a/src/tables/GSUB.js b/src/tables/GSUB.js index 757bf5a1..c14112a3 100644 --- a/src/tables/GSUB.js +++ b/src/tables/GSUB.js @@ -59,11 +59,12 @@ let GSUBLookup = new r.VersionedStruct('lookupType', { 8: { // Reverse Chaining Contextual Single Substitution substFormat: r.uint16, coverage: new r.Pointer(r.uint16, Coverage), + backtrackGlyphCount: r.uint16, backtrackCoverage: new r.Array(new r.Pointer(r.uint16, Coverage), 'backtrackGlyphCount'), lookaheadGlyphCount: r.uint16, lookaheadCoverage: new r.Array(new r.Pointer(r.uint16, Coverage), 'lookaheadGlyphCount'), glyphCount: r.uint16, - substitutes: new r.Array(r.uint16, 'glyphCount') + substitute: new r.LazyArray(r.uint16, 'glyphCount') } }); diff --git a/test/data/NotoCoptic/NotoSansCoptic-Regular.ttf b/test/data/NotoCoptic/NotoSansCoptic-Regular.ttf new file mode 100644 index 00000000..0bfae4be Binary files /dev/null and b/test/data/NotoCoptic/NotoSansCoptic-Regular.ttf differ diff --git a/test/data/NotoCoptic/OFL.txt b/test/data/NotoCoptic/OFL.txt new file mode 100644 index 00000000..ac06190f --- /dev/null +++ b/test/data/NotoCoptic/OFL.txt @@ -0,0 +1,93 @@ +Copyright 2022 The Noto Project Authors (https://github.com/notofonts/coptic) + +This Font Software is licensed under the SIL Open Font License, Version 1.1. +This license is copied below, and is also available with a FAQ at: +https://scripts.sil.org/OFL + + +----------------------------------------------------------- +SIL OPEN FONT LICENSE Version 1.1 - 26 February 2007 +----------------------------------------------------------- + +PREAMBLE +The goals of the Open Font License (OFL) are to stimulate worldwide +development of collaborative font projects, to support the font creation +efforts of academic and linguistic communities, and to provide a free and +open framework in which fonts may be shared and improved in partnership +with others. + +The OFL allows the licensed fonts to be used, studied, modified and +redistributed freely as long as they are not sold by themselves. The +fonts, including any derivative works, can be bundled, embedded, +redistributed and/or sold with any software provided that any reserved +names are not used by derivative works. The fonts and derivatives, +however, cannot be released under any other type of license. The +requirement for fonts to remain under this license does not apply +to any document created using the fonts or their derivatives. + +DEFINITIONS +"Font Software" refers to the set of files released by the Copyright +Holder(s) under this license and clearly marked as such. This may +include source files, build scripts and documentation. + +"Reserved Font Name" refers to any names specified as such after the +copyright statement(s). + +"Original Version" refers to the collection of Font Software components as +distributed by the Copyright Holder(s). + +"Modified Version" refers to any derivative made by adding to, deleting, +or substituting -- in part or in whole -- any of the components of the +Original Version, by changing formats or by porting the Font Software to a +new environment. + +"Author" refers to any designer, engineer, programmer, technical +writer or other person who contributed to the Font Software. + +PERMISSION & CONDITIONS +Permission is hereby granted, free of charge, to any person obtaining +a copy of the Font Software, to use, study, copy, merge, embed, modify, +redistribute, and sell modified and unmodified copies of the Font +Software, subject to the following conditions: + +1) Neither the Font Software nor any of its individual components, +in Original or Modified Versions, may be sold by itself. + +2) Original or Modified Versions of the Font Software may be bundled, +redistributed and/or sold with any software, provided that each copy +contains the above copyright notice and this license. These can be +included either as stand-alone text files, human-readable headers or +in the appropriate machine-readable metadata fields within text or +binary files as long as those fields can be easily viewed by the user. + +3) No Modified Version of the Font Software may use the Reserved Font +Name(s) unless explicit written permission is granted by the corresponding +Copyright Holder. This restriction only applies to the primary font name as +presented to the users. + +4) The name(s) of the Copyright Holder(s) or the Author(s) of the Font +Software shall not be used to promote, endorse or advertise any +Modified Version, except to acknowledge the contribution(s) of the +Copyright Holder(s) and the Author(s) or with their explicit written +permission. + +5) The Font Software, modified or unmodified, in part or in whole, +must be distributed entirely under this license, and must not be +distributed under any other license. The requirement for fonts to +remain under this license does not apply to any document created +using the Font Software. + +TERMINATION +This license becomes null and void if any of the above conditions are +not met. + +DISCLAIMER +THE FONT SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, +EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO ANY WARRANTIES OF +MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT +OF COPYRIGHT, PATENT, TRADEMARK, OR OTHER RIGHT. IN NO EVENT SHALL THE +COPYRIGHT HOLDER BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, +INCLUDING ANY GENERAL, SPECIAL, INDIRECT, INCIDENTAL, OR CONSEQUENTIAL +DAMAGES, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING +FROM, OUT OF THE USE OR INABILITY TO USE THE FONT SOFTWARE OR FROM +OTHER DEALINGS IN THE FONT SOFTWARE. diff --git a/test/shaping.js b/test/shaping.js index dc005ea0..23878b09 100644 --- a/test/shaping.js +++ b/test/shaping.js @@ -582,4 +582,17 @@ describe('shaping', function () { test('SHBALI-2/12', 'NotoSans/NotoSansBalinese-Regular.ttf', "ᬓ᭄ᭅᬸ", '23+2275|162+0|60@0,-1000+0'); }); }); + + describe('reverse chaining contextual single substitution (GSUB Type 8)', function () { + // Noto Sans Coptic's ccmp feature applies a Type 8 lookup that converts + // basic combining-macron glyphs to their `.cap` variants when followed + // by another macron in the run — the spec-mandated reverse-direction + // pass means the second macron's earlier-stage substitution must be + // visible as the first macron's lookahead context. Matching HarfBuzz's + // output here proves Type 8 actually fired in the right order. + test('GSUB Type 8: Coptic stacked-macron .cap variant', + 'NotoCoptic/NotoSansCoptic-Regular.ttf', + 'Ⲁ̅ⲁ̅', + '33+633|196@-319,0+0|34+574|199@-291,0+0'); + }); });