The Infinality bytecode interpreter is removed in favor of the new v40 TrueType
interpreter. In the past, the Infinality interpreter provided support for
ClearType-style hinting instructions while the default interpreter (then v35)
provided support only for original TrueType-style instructions. The v40
interpreter corrects this deficiency, so the Infinality interpreter is no longer
necessary.
To understand why the Infinality interpreter is no longer necessary, we should
understand how ClearType differs from TrueType and how the v40 interpreter
works. The following is a summary of information available on the FreeType
website [1] mixed with my own editorializing.
TrueType instructions use horizontal and vertical hints to improve glyph
rendering. Before TrueType, fonts were only vertically hinted; horizontal hints
improved rendering by snapping stems to pixel boundaries. Horizontal hinting is
a risk because it can significantly distort glyph shapes and kerning. Extensive
testing at different resolutions is needed to perfect the TrueType
hints. Microsoft invested significant effort to do this with its "Core fonts for
the Web" project, but few other typefaces have seen this level of attention.
With the advent of subpixel rendering, the effective horizontal resolution of
most displays increased significantly. ClearType eschews horizontal hinting in
favor of horizontal supersampling. Most fonts are designed for the Microsoft
bytecode interpreter, which implements a compatibility mode with
TrueType-style (horizontal and vertical) instructions. However, applying the
full horizontal hints to subpixel-rendered fonts leads to color fringes and
inconsistent stem widths. The Infinality interpreter implements several
techniques to mitigate these problems, going so far as to embed font- and
glyph-specific hacks in the interpreter. On the other hand, the v40 interpreter
ignores the horizontal hinting instructions so that glyphs render as they are
intended to on the Microsoft interpreter. Without the horizontal hints, the
problems of glyph and kerning distortion, color fringes, and inconsistent stem
widths--the problems the Infinality interpreter was created to solve--simply
don't occur in the first place.
There are also security concerns which motivate removing the Infinality patches.
Although there is an updated version of the Infinality interpreter for FreeType
2.7, the lack of a consistent upstream maintainer is a security concern. The
interpreter is a Turing-complete virtual machine which has had security
vulnerabilities in the past. While the default interpreter is used in billions
of devices and is maintained by an active developer, the Infinality interpreter
is neither scrutinized nor maintained. We will probably never know if there are
defects in the Infinality interpreter, and if they were discovered they would
likely never be fixed. I do not think that is an acceptable situtation for a
core library like FreeType.
Dropping the Infinality patches means that font rendering will be less
customizable. I think this is an acceptable trade-off. The Infinality
interpreter made many compromises to mitigate the problems with horizontal
hinting; the main purpose of customization is to tailor these compromises to the
user's preferences. The new interpreter does not have to make these compromises
because it renders fonts as their designers intended, so this level of
customization is not necessary.
The Infinality-associated patches are also removed from cairo. These patches
only set the default rendering options in case they aren't set though
Fontconfig. On NixOS, the rendering options are always set in Fontconfig, so
these patches never actually did anything for us!
The Fontconfig test suite is patched to account for a quirk in the way PCF fonts
are named.
The fontconfig option `hintstyle` is no longer configurable in NixOS. This
option selects the TrueType interpreter; the v40 interpreter is `hintslight` and
the older v35 interpreter is `hintmedium` or `hintfull` (which have actually
always been the same thing). The setting may still be changed through the
`localConf` option or by creating a user Fontconfig file.
Users with HiDPI displays should probably disable hinting and antialiasing: at
best they have no visible effect.
The fontconfig-ultimate settings are still available in NixOS, but they are no
longer the default. They still work, but their main purpose is to set rendering
quirks which are no longer necessary and may actually be
detrimental (e.g. setting `hintfull` for some fonts). Also, the vast array of
font substitutions provided is not an appropriate default; the default setting
should be to give the user the font they asked for.
[1]. https://www.freetype.org/freetype2/docs/subpixel-hinting.html
The nixbld group belongs to nix-daemon and you really don't want to be
in it. If you are in it, nix-daemon will kill your processes when you
least expect it :)
It'd be better to do the update as an unprivileged user; for
now, we do our best to minimize the surface available. We
filter mount syscalls to prevent the process from undoing the fs
isolation.
Resolve download.dnscrypt.org using hostip with a bootstrap
resolver (hard-coded to Google Public DNS for now), to ensure
that we can get an up-to-date resolver list without working name
service lookups. This makes us more robust to the upstream
resolver list getting out of date and other DNS configuration
problems.
We use the curl --resolver switch to allow https cert validation
(we'd need to do --insecure if using just the ip addr). Note
that we don't rely on https for security but it's nice to have
it ...
Use mkMerge to make the code a little more ergonomic and easier
to follow (to my eyes, anyway ...). Also take the opportunity
to do some minor cleanups & tweaks, but no functional changes.
After the change of the bonding options, the examples were not quite correct.
The diff is over-the top because the new `let` needs everything indented.
Also add a small docstring to the `networkd` attr in the networking test.
Set `networking.networkmanager.wifi.macAddress` or `networking.networkmanager.ethernet.macAddress`
to one of these values to change your macAddress.
* "XX:XX:XX:XX:XX:XX": set the MAC address of the interface.
* "permanent": use the permanent MAC address of the device.
* "preserve": don’t change the MAC address of the device upon activation.
* "random": generate a randomized value upon each connect.
* "stable": generate a stable, hashed MAC address.
See https://blogs.gnome.org/thaller/2016/08/26/mac-address-spoofing-in-networkmanager-1-4-0/ for more information
We only care about /nix/store because its contents might be out of
sync with /nix/var/nix/db. Syncing other filesystems might cause
unnecessary delays or hangs (e.g. I encountered a case where an NFS
mount was taking a very long time to sync).
