Make fontdiff obsolete

[davelab6]

https://github.com/googlefonts/fontdiff hasn't been updated for about 2-3 years. Sascha Brawer developed it, but then left Google.

I'm filing this issue to discuss what would be needed for diffbrowsers to be able to complete replace it.

In chat just now @marekjez86 noted that a key feature of fontdiff is that it can take as input an arbitrary simplified HTML file with a text to compare, which is related to #23.

There's also some tools in https://bitbucket.org/LindenbergSW/fontdoctools/src/master/ which might be relevant (sample output @ https://lindenbergsoftware.com/en/tools/R%C3%B6ntgen.NotoSansDevanagari.html)

And there's also https://github.com/silnrsi/fontproof

[m4rc1e]

If we did implement this functionality, I'd prefer to see it in Diffenator. Diffbrowsers exists solely to diff browser rendering quality.

GFRegression does allow users to input their own sample text and make a diff (in GUI only, no api access). It's more primitive than fontdiff though.

My plan is to eventually allow Diffenator to display changes in real sample text/words. This means we'll get more realistic results and testers won't need to roll their own test strings. Here's the current progress.

• [X] Refactor image generator so it can handle words, bidi input etc (basically make a primitive word processor)
• [x] Collect sample text. I'm thinking of using Unicode UDHR, https://github.com/unicode-org/udhr
• [ ] add cli option to allow users to see changes in sentences, not just individual characters
• [ ] Produce a mapping which will map individual characters to words (still thinking about the best approach for this)