Re: how reliable is rendering of complex scripts?

[Werner LEMBERG <wl@gnu.org>]

>> The nice thing about `hb-shape' is that it doesn't output graphics
>> but a textual representation of the GSUB and GPOS manipulation
>> results (including reordering of the input).  In other words, Emacs
>> could use the same output format in a special test mode, making
>> comparisons very simple – and automated!
> 
> Too bad.

Hmm.  I consider this as a benefit, since comparison of images is much
harder, especially if the exact environment differs.  In particular,
for two identical, correct GSUB/GPOS representations of a text string,
you can easily get different rendering results for GDI and DWrite
ClearType (on Windows), normal grayscale rendering and auto-hinting
from FreeType, grayscale rendering on older Windows versions and Mac
OS X, different color filters used on different platforms etc., etc.

> It means these tests cannot be easily used by Emacs, because [...]

Well, if you need graphic output, use `hb-view', which creates images
of text strings.

> Perhaps a good first step would be for someone to produce pictures
> of the rendered texts from those tests (using Harfbuzz or anything
> else that can be used as reference), and then we could compare that
> with what Emacs produces for the same texts, and see how good or bad
> we are doing.

This is *exactly* what should be avoided IMHO.  It's both far too much
work and too imprecise.


    Werner