[ft-devel] Taming CFF_CONFIG_OPTION_DARKENING_PARAMETER_Y* for a gamma of ~2.2/sRGB?

[Nikolaus Waxweiler]

Hello list,
I've been playing around with the CFF renderer again because font 
rendering is a dear topic to me. What immediately stands out is that 
rendered fonts are much thicker than what the autohinter puts out. This 
creates a somewhat strong contrast between local .otfs and web fonts 
when browsing the net. Now, Dave Arnold said in an old mail to list that 
"The stem darkening function assumes blending with a gamma close to 1.8".

* What values/formula should I use with a gamma close to 2.2 or sRGB?
* Shouldn't that be the default for a feature that's turned on by 
default? I currently use Y1-Y4: 300, 200, 200, 0.
* Arnold wrote that "gamma correction" is necessary. What part of the 
rendering stack does that? And is it, in experience, implemented and 
working on the usual Linux systems?
* What's the state of stem darkening for the autohinter for e.g. 
TrueType fonts? I see that Infinality has given up on maintaining his 
patch set. A shared stem darkening would improve the coexistence of 
Adobe-CFF-rendered and autohinted fonts.

It saddens me that this great little piece of rendering code gets so 
little publicity and (font) support from OSS communities... Shipping the 
URW35, DejaVu and Liberation font families as properly hinted .otfs 
instead of .pfbs and .ttfs would be a start.

Regards,
Nikolaus