descender is assumed to be negative, but zero should be allowed

[skreborn]

Expected Behavior

The Material Icons font to be usable with new Font({ ... }).

Current Behavior

The font can not be used, because the constructor throws an error:

Uncaught (in promise) When creating a new Font object, descender is required.

Possible Solution

The bug occurs because Font expects descender to be non-zero, while it is a valid value. A simple fix would be to change the checks as follows:

checkArgument(typeof options.descender === 'number', 'When creating a new Font object, descender is required.');
checkArgument(options.descender <= 0, 'Descender should be negative or zero (e.g. -512).');

Although highly unlikely, I suppose it would also be correct to do the same with ascender:

checkArgument(typeof options.ascender === 'number', 'When creating a new Font object, ascender is required.');

Steps to Reproduce (for bugs)

const opentype = require('opentype.js');

fetch('material-icons.otf')
  .then(response => response.arrayBuffer())
  .then(buffer => {
    const font = opentype.parse(buffer);

    new opentype.Font({
      familyName: 'Material Icons',
      styleName: font.names.fontSubfamily.en,
      unitsPerEm: font.unitsPerEm,
      ascender: font.ascender,
      // While `parse` correctly uses zero as a value, `Font` won't accept it
      descender: font.descender,
      glyphs: []
    })
  });

Context

The font is read correctly in the playground and the inspector displays its descender to be zero, as expected, but the library version doesn't produce the same results, unfortunately.

Your Environment

• Version used: 0.8.0
• Font used: Material Icons

[Connum]

This was already fixed some time ago via #422