Arabic text is not rendered correctly

Expected Behavior

Let’s take the following arabic sentence: بِسْمِ الله الرَّحْمٰنِ الرَّحِيمِ’ Natively it renders to the following form:

Current Behavior

With current version of opentype.js (and even with merged PR #361 and #362 from @solomancode it looks like this:

• serifs look different
• last word looks significantly different
• the semi-vertical lines have incorrect x position and are a bit lower
• second word (allah) misses a “w”

Steps to Reproduce

Create following js file in opentype.js directory:

var opentype = require('./dist/opentype');
var fs = require("fs");
var Canvas = require("canvas").Canvas;

opentype.load('fonts/Scheherazade-Bold.ttf', function(err, font) {
    if (err) {
         alert('Font could not be loaded: ' + err);
    } else {
        var canvas = new Canvas(1000, 500, "png");
        var ctx = canvas.getContext('2d');
        var path = font.getPath('بِسْمِ الله الرَّحْمٰنِ الرَّحِيمِ', 0, 200, 100);
        path.draw(ctx);
        var buf = canvas.toBuffer();
        fs.writeFileSync("test.png", buf);
    }
});

(additionally, use npm install canvas to be able to render font to png))

Your Environment

• Version used: 0.11.0
• Font used: Scheherazade-Bold.ttf
• Browser Name and version: Chrome Canary
• Operating System and version (desktop or mobile): Windows 10

[moyogo]

Regarding the Allah word, Scheherazade is following the Unicode specification. Fonts should only form the allah ligature when the shadda and the superscript alef are present in the character sequence. See the note about FDF2 in https://www.unicode.org/versions/Unicode11.0.0/ch09.pdf#page=32:

U+FDF2 ARABIC LIGATURE ALLAH ISOLATED FORM is a very common ligature, used to display the name of God. When the formation of the allah ligature is desired, the recommended way to represent the word would be <alef, lam, lam, shadda, superscript alef, heh><0627, 0644, 0644, 0651, 0670, 0647>. In non-Arabic languages, other forms of heh, such as heh goal (U+06C1), may also form the ligature. Extra care should be taken not to form the ligature in the absence of the shadda and the superscript alef, as the sequences <alef, lam, lam, heh> and <alef, lam, lam, shadda, heh> exist in Persian and other languages with different meanings or pronunciations, where the formation of the ligature would be incorrect and inappropriate.

However many fonts, including widely used system fonts, do form the ligature without the shadda and superscript alef being present in the character sequence. So it is understandable that there is such a user expectation but it is problematic for the reasons given in the Unicode standard.

[solomancode]

I don’t understand your question, واللـهِ That’s ‘Kasra’ not Shadda, and it’s not related to the spec.