Full script font support. about fontkit

[devongovett]

Fontkit does support OpenType and AAT layout. It may be that you just need to enable the right feature, or it could be a bug. Can you send over a link to the font you're using and the code you're using to render? Thanks!

[achrist]

I'm using Pacifico Regular as my test font. It can be downloaded from Google Fonts. Some example code is below:

  const font = scene.renderer.fonts.fonts['Pacifico-Regular'];
  const size = 40;
  const gridToPx = size / font.unitsPerEm;
  const ascent = font.ascent * gridToPx;
  const glyphRun = font.layout('This is a test.');
  const { glyphs, positions } = glyphRun;

  context.save();
  context.scale(1, -1);

  let xOffset = 0;

  for (let i = 0; i < glyphs.length; i++) {
    const glyph = glyphs[i];
    const position = positions[i];

    context.save();
    context.fillStyle = 'black';
    context.translate(xOffset, -ascent);
    context.beginPath();
    glyph.render(context, size);
    context.restore();

    xOffset += position.xAdvance * gridToPx;
  }

  context.restore();

I've tried to enable all of the available features for the font but none of them seem to do the trick. The available features according to the font file are:

'aalt',
'calt',
'case',
'dlig',
'fina',
'frac',
'liga',
'ordn',
'salt',
'ss01',
'ss02',
'sups',
'kern',
'mark',
'mkmk'

[Pomax]

Based on previous work with a different library that had the same issue: if the features toggling is not doing the trick, this might be a left-side bearing issue, with the glyphs placed at (0,0) rather than at (-glyph.lsb,0)

[andersmelander]

I just reproduced this exact problem in my own shaper. My shaper is independent from FontKit but as far as I can tell the cause of the problem is the same.

The problem in my shaper was the GSUB 'calt' feature in the Pacifico font. The 'calt' feature contains two type 6 (chaining contextual substitution) lookups:

1. The first lookup matches a glyph followed by a glyph. There is no substitution for this lookup (i.e. do nothing).
2. The second lookup matches a glyph followed by nothing. The substitution is the .fina form of the glyph.

The problem is that the shaper considers a lookup match with no substitution records (case 1 above) a non-match and because of this case 2 above is executed for all glyphs.

The problem can be emulated in the Crowbar OpenType debugger by disabling the 'calt' feature and enabling the 'fina' feature.

Edit: I've now looked at the relevant FontKit code and I can not see that it has the problem my code had.

fontkit/src/opentype/OTProcessor.js

Line 218 in a5fe0a1

applyLookupList(lookupRecords) {