Re: [ft-devel] Autohinter: stem darkening, first rough prototype

[Nikolaus Waxweiler]

> Where's the problem?  The auto-hinter provides different standard
> width values depending on the script.  It tries up to three characters
> (cf. the last three arguments to the `SCRIPT' macro in file
> `afscript.h') in function `af_latin_metrics_init_widths' for finding a
> standard width.  As soon as we have found a glyph (the first hit
> wins), all stems of the glyph are computed, which are then sorted and
> quantized.  The result of this process is stored in the `widths' array
> of `AF_LatinAxisRec'; the smallest one is handled as the default
> width.  If no width could be determined, a default value of 50/2048 em
> is used.

> I don't understand this. Please elaborate.

Thanks for the explanation. The source code needs comments like that :)

In my first prototype, I tried to get a face-wide stdVW and modified 
af_latin_metrics_init_widths to upload whatever is computed to 
AF_FaceGlobals. Then I found that when displaying all glyphs in a font 
with ftview, the first few glyphs don't produce anything (spoiler: 
af_cjk_metrics_init_widths was here, maybe because #define 
AF_STYLE_FALLBACK AF_STYLE_HANI_DFLT), and later runs produced different 
standard_widths (for different scripts). My hack was to look at each run 
of init_width and take the biggest value that any of it produces, and, 
depending on the font, recompute the darkening amount multiple times per 
size (each time a bigger standard_width came along). That was quite ugly 
and probably buggy.

So by "in a controlled way", I mean run all script analyzers from 
af_face_globals_get_standard_widths() upon metrics initialization and do 
something meaningful with the produced standard_widths, ONCE PER SIZE 
before anything else is done.

Hm, I just had the idea to extend the writing system class with a 
AF_WritingSystem_GetStdWidthsFunc. Will experiment later.

And "hard-to-follow" was a general comment. I find the excessive 
preprocessor use in FT difficult to follow and it took me a while to 
understand how the different parts of the autohinter click together and 
what is done in what order...

> Direct access is not possible except with ugly hacks.

Alright. My idea was to listen to what the private dict of a font said 
before computing it the hard way. So, only Postscript fonts get listened 
to now ;)