How can I use and extract kerning pairs from from GPOS table in Opentype fonts to correctly show glyphs as Path2D in Java?

Question

This question is related to a few questions that have been asked long time ago. I saw comments that Opentype fonts were not supported in Java, but this was

Answer 1

Problem solved!

An advice: if you are trying to do this in Java you are losing your time. This problem was solved simply using Opentype.js and the site https://opentype.js.org, but particularly glyph inspector and font inspector.

I downloaded both code by copying and pasting from page source. I then modified glyph inspector to do the job. You need to go deeply into Opentype.js to get the kerning pairs, though, but it is all there (check code below).

I ended up porting the entire program to JavaScript. I didn't program JavaScript too much before. Therefore, it must be extremely easy for whom already programs in JavaScript. This program just generates a Java class with the glyphs, the kerning pairs and widths (the advanceWidth for each glyph).

Here, an image to show the result:

The code below in JavaScript dumps the GPOS kerning table into the string text, presenting a list of sets containing the second character and the kern value in each line, while the first character of the pair appears as a Java character at the beginning of the line. Notice, that glyph indexes are avoided by using the ASCII codes of the characters.

This only dumps ' '(space) to '}', which is what is useful for English language. To expand to other characters just use Unicode.

<!-- indoc: true -> writes in HTML on this page  -->
const indoc = true;
const nl = (indoc) ? "<br>" : "\n";
var chars = font.tables.cmap.glyphIndexMap;
var g1,g2;
var i, j, kern;
var text = "";
for ( i = 32; i < 126; i++ ) {
    g1 = font.glyphs.get(chars[i]);
    text += "'" +
    (( i == 39 || i == 92) ? "\\" + String.fromCharCode(i) : String.fromCharCode(i) )+ "'";
    for ( j = 32; j < 126; j++ ) {
        g2 = font.glyphs.get(chars[j]);
        if ( (kern = font.getKerningValue(g1,g2)) !== 0 ) {
            text += ", { '" +
            (( j == 39 || j == 92) ? "\\" + String.fromCharCode(j) : String.fromCharCode(j) )+
            "', " + kern + " }";
        }
    }
    text += nl;
}