[Development] about the Cocoa/Freetype fontengine

[René J. V. Bertin]

Nikolaus Waxweiler wrote:

> I think you have to carefully match the rendering of CoreText (and its'
> darkening algorithm) for users not to notice. At that point, you might
> as well use CoreText, unless you have something very specific in mind.

Remember that there's also the issue of getting the exact same font metrics 
which is important for certain users.

> People notice different font rendering.

Yes - but they're not likely to complain if the different look also looks 
better. And even then ... how many users complained about window titles looking 
blurry when KWin started using QtQuick for rendering titlebars?

> The performance hit is measurable in the rendering benchmark tool

Measurable in a benchmark tool doesn't mean there are performance issues. I've 
been using Infinality on a very slow system, without any ill effects.

> consistency. Sit a Core Web font next to some random Google Font font on
> the internet and they'll look jarringly different, like each used a

If you mean fonts rendered by FreeType with and without Infinality looks 
jarringly different, then yes, that can be the case at regular point sizes on 
regular density displays. Which is the whole point: with the result looks 
jarringly better.

> No, incorrectly hits the mark. As soon as your rendered glyph image
> contains shades of gray, you MUST use linear alpha blending and gamma
> correction. Everything else is incorrect.
> The Windows and Mac platform
> have been doing that for decades, X11 libs never did to my knowledge.

Erm, I'm talking about KDE desktops using Qt4 or better, which have the option 
to activate sub-pixel rendering and hinting (which will be on by default IIRC). 
Basic X11 font rendering doesn't, indeed. Instead it relied on pre-rendered 
bitmap fonts like for a high-resolution matrix printer. And curiously those 
fonts could be displayed 100% correct - with moiré effects and blurring between 
the display phosphor and our retina taking care of making the letters look 
smooth enough to be pleasant. I still use some fonts like that (Monaco in 
particular) in my xterms, that I've been preserving from my PhD days on a Mac 
IIx running A/UX 2.0 . 

Either way, a long as we're talking about vector fonts rendered on a raster 
display the term correct has a very relative meaning.

> The CFF darkener delivers the best
> looking results so far, as it only counters the thinning such that the
> font looks as meaty as before gamma correction.

Again, that's in the eye of the beholder, but I still find that the results look 
better with than without the Infinality patch set. The only regression (due to 
your CFF darkener or to the FT+FC patches) is in a single font family so far, 
which looks washed out with the default gamma correction. That's actually due to 
something in the FontConfig "Ultimate" patch or tweaked config files.
I have no idea if those are CFF fonts and can't find a reference to the family in 
the .conf files either.

> (just look at all the fixing Infinality has to do; hinting can be a very
> seat-of-the-pants business)

It is, inevitably. It's aimed at fooling human perception and as such cannot be 
an exact science (unless you're a biologist or "assimilated" neuroscientist :)).

Anyway, whether or not "we" use Infinality is not Qt's business. Or rather, it's 
not up to Qt to tell us what we should consider to look better and then take 
steps to make it impossible to use that patch set.

The issue at hand here is whether or not Qt should/could allow users to use font 
rendering based on FreeType+FontConfig across the main platforms, with as the 
main argument the fact that this will allow (near) perfect cross-platform 
homogeneity in text rendering. The default should evidently be to use the 
platform native font engine (but it'd be nice if there were at least an env. 
variable for users to select their preferred engine and/or a way to do so via 
e.g. a platform theme plugin like the plasma-integration plugin or my 
github:RJVB/osx-integration.git).

I've posted a few side-by-side comparisons: 
https://bugreports.qt.io/browse/QTBUG-65510

>> I probably would if I knew how.
> 
> export FREETYPE_PROPERTIES=cff:no-stem-darkening=1

I see absolutely no difference between the two. Maybe simply because I'm not 
using any CFF fonts.

R.