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import unicode from 'unicode-properties';
/**
* This class is used when GPOS does not define 'mark' or 'mkmk' features
* for positioning marks relative to base glyphs. It uses the unicode
* combining class property to position marks.
*
* Based on code from Harfbuzz, thanks!
* https://github.com/behdad/harfbuzz/blob/master/src/hb-ot-shape-fallback.cc
*/
export default class UnicodeLayoutEngine {
constructor(font) {
this.font = font;
}
positionGlyphs(glyphs, positions) {
// find each base + mark cluster, and position the marks relative to the base
let clusterStart = 0;
let clusterEnd = 0;
for (let index = 0; index < glyphs.length; index++) {
let glyph = glyphs[index];
if (glyph.isMark) { // TODO: handle ligatures
clusterEnd = index;
} else {
if (clusterStart !== clusterEnd) {
this.positionCluster(glyphs, positions, clusterStart, clusterEnd);
}
clusterStart = clusterEnd = index;
}
}
if (clusterStart !== clusterEnd) {
this.positionCluster(glyphs, positions, clusterStart, clusterEnd);
}
return positions;
}
positionCluster(glyphs, positions, clusterStart, clusterEnd) {
let base = glyphs[clusterStart];
let baseBox = base.cbox.copy();
// adjust bounding box for ligature glyphs
if (base.codePoints.length > 1) {
// LTR. TODO: RTL support.
baseBox.minX += ((base.codePoints.length - 1) * baseBox.width) / base.codePoints.length;
}
let xOffset = -positions[clusterStart].xAdvance;
let yOffset = 0;
let yGap = this.font.unitsPerEm / 16;
// position each of the mark glyphs relative to the base glyph
for (let index = clusterStart + 1; index <= clusterEnd; index++) {
let mark = glyphs[index];
let markBox = mark.cbox;
let position = positions[index];
let combiningClass = this.getCombiningClass(mark.codePoints[0]);
if (combiningClass !== 'Not_Reordered') {
position.xOffset = position.yOffset = 0;
// x positioning
switch (combiningClass) {
case 'Double_Above':
case 'Double_Below':
// LTR. TODO: RTL support.
position.xOffset += baseBox.minX - markBox.width / 2 - markBox.minX;
break;
case 'Attached_Below_Left':
case 'Below_Left':
case 'Above_Left':
// left align
position.xOffset += baseBox.minX - markBox.minX;
break;
case 'Attached_Above_Right':
case 'Below_Right':
case 'Above_Right':
// right align
position.xOffset += baseBox.maxX - markBox.width - markBox.minX;
break;
default: // Attached_Below, Attached_Above, Below, Above, other
// center align
position.xOffset += baseBox.minX + (baseBox.width - markBox.width) / 2 - markBox.minX;
}
// y positioning
switch (combiningClass) {
case 'Double_Below':
case 'Below_Left':
case 'Below':
case 'Below_Right':
case 'Attached_Below_Left':
case 'Attached_Below':
// add a small gap between the glyphs if they are not attached
if (combiningClass === 'Attached_Below_Left' || combiningClass === 'Attached_Below') {
baseBox.minY += yGap;
}
position.yOffset = -baseBox.minY - markBox.maxY;
baseBox.minY += markBox.height;
break;
case 'Double_Above':
case 'Above_Left':
case 'Above':
case 'Above_Right':
case 'Attached_Above':
case 'Attached_Above_Right':
// add a small gap between the glyphs if they are not attached
if (combiningClass === 'Attached_Above' || combiningClass === 'Attached_Above_Right') {
baseBox.maxY += yGap;
}
position.yOffset = baseBox.maxY - markBox.minY;
baseBox.maxY += markBox.height;
break;
}
position.xAdvance = position.yAdvance = 0;
position.xOffset += xOffset;
position.yOffset += yOffset;
} else {
xOffset -= position.xAdvance;
yOffset -= position.yAdvance;
}
}
return;
}
getCombiningClass(codePoint) {
let combiningClass = unicode.getCombiningClass(codePoint);
// Thai / Lao need some per-character work
if ((codePoint & ~0xff) === 0x0e00) {
if (combiningClass === 'Not_Reordered') {
switch (codePoint) {
case 0x0e31:
case 0x0e34:
case 0x0e35:
case 0x0e36:
case 0x0e37:
case 0x0e47:
case 0x0e4c:
case 0x0e3d:
case 0x0e4e:
return 'Above_Right';
case 0x0eb1:
case 0x0eb4:
case 0x0eb5:
case 0x0eb6:
case 0x0eb7:
case 0x0ebb:
case 0x0ecc:
case 0x0ecd:
return 'Above';
case 0x0ebc:
return 'Below';
}
} else if (codePoint === 0x0e3a) { // virama
return 'Below_Right';
}
}
switch (combiningClass) {
// Hebrew
case 'CCC10': // sheva
case 'CCC11': // hataf segol
case 'CCC12': // hataf patah
case 'CCC13': // hataf qamats
case 'CCC14': // hiriq
case 'CCC15': // tsere
case 'CCC16': // segol
case 'CCC17': // patah
case 'CCC18': // qamats
case 'CCC20': // qubuts
case 'CCC22': // meteg
return 'Below';
case 'CCC23': // rafe
return 'Attached_Above';
case 'CCC24': // shin dot
return 'Above_Right';
case 'CCC25': // sin dot
case 'CCC19': // holam
return 'Above_Left';
case 'CCC26': // point varika
return 'Above';
case 'CCC21': // dagesh
break;
// Arabic and Syriac
case 'CCC27': // fathatan
case 'CCC28': // dammatan
case 'CCC30': // fatha
case 'CCC31': // damma
case 'CCC33': // shadda
case 'CCC34': // sukun
case 'CCC35': // superscript alef
case 'CCC36': // superscript alaph
return 'Above';
case 'CCC29': // kasratan
case 'CCC32': // kasra
return 'Below';
// Thai
case 'CCC103': // sara u / sara uu
return 'Below_Right';
case 'CCC107': // mai
return 'Above_Right';
// Lao
case 'CCC118': // sign u / sign uu
return 'Below';
case 'CCC122': // mai
return 'Above';
// Tibetan
case 'CCC129': // sign aa
case 'CCC132': // sign u
return 'Below';
case 'CCC130': // sign i
return 'Above';
}
return combiningClass;
}
}