venam
(This is part of the podcast discussion extension)

Fonts on Free-Unixes

Link of the recording [ https://raw.githubusercontent.com/nixers...-02-26.mp3 http://podcast.nixers.net/feed/download....02-261.mp3 ]

The font stack is so complex, let's clear that up a bit.

References:

- TTY:
https://github.com/talamus/rw-psf
http://askubuntu.com/questions/173220/ho...ty-console
http://unix.stackexchange.com/questions/...-a-otf-one
https://www.freebsd.org/doc/en/articles/...ticle.html
https://wiki.freebsd.org/Newcons
http://www.openbsd.org/faq/faq7.html
https://en.wikipedia.org/wiki/Linux_console
https://nixers.net/showthread.php?tid=552
https://en.wikipedia.org/wiki/Glyph_Bitm...ion_Format

- Locale & UTF-8:
http://www.in-ulm.de/~mascheck/X11/input8bit.html
http://michal.kosmulski.org/computing/ar...icode.html
https://en.wikipedia.org/wiki/Open-sourc..._typefaces
http://stackoverflow.com/questions/20226...re-applied
http://unix.stackexchange.com/questions/...c-do#87748
https://docs.oracle.com/cd/E23824_01/htm...glmbx.html
http://www.unix.com/unix-for-dummies-que...ocale.html
http://www.in-ulm.de/~mascheck/locale/
http://unifont.org/fontguide/

- Font files:
https://www.freetype.org/freetype2/docs/...phs-1.html
https://www.freetype.org/freetype2/docs/index.html

- Rendering (FreeType):
http://userguide.icu-project.org/layoute...C-Overview
https://en.wikipedia.org/wiki/Apple_Advanced_Typography
https://en.wikipedia.org/wiki/Font_rasterization
https://freddie.witherden.org/pages/font-rasterisation
https://en.wikipedia.org/wiki/FreeType
https://www.freetype.org/freetype2/docs/...phs-5.html
https://bbs.archlinux.org/viewtopic.php?id=33955
https://keithp.com/~keithp/talks/xtc2001/paper/
https://en.wikipedia.org/wiki/Subpixel_rendering
How subpixel rendering works: https://www.grc.com/ctwhat.htm
http://www.osnews.com/story/18166/Interv...-Freetype/
http://behdad.org/text/
https://www.x.org/wiki/guide/client-ecosystem/

- MacOS:
https://en.wikipedia.org/wiki/Fonts_on_Macintosh
https://en.wikipedia.org/wiki/Quartz_(graphics_layer)

- Stack:
https://weirdfellow.wordpress.com/2010/07/25/insanity/
https://weirdfellow.wordpress.com/tag/freetype/
http://www.pango.org/
https://kb.iu.edu/d/aytm
https://en.wikipedia.org/wiki/File:GTK%2...ecture.svg
http://roxlu.com/2014/046/rendering-text...d-freetype
https://en.wikipedia.org/wiki/Pango
https://en.wikipedia.org/wiki/HarfBuzz
https://www.freedesktop.org/wiki/HarfBuzz/
https://wiki.archlinux.org/index.php/X_L...escription
http://unix.stackexchange.com/questions/...fonts#7483
https://en.wikipedia.org/wiki/X_Font_Server
https://specifications.freedesktop.org/x...c-0.5.html

- Generic Management (Fontconfig):
http://tldp.yolinux.com/HOWTO/Font-HOWTO.html
https://wiki.archlinux.org/index.php/Fonts
https://wiki.archlinux.org/index.php/font_configuration
https://access.redhat.com/documentation/...fonts.html
https://wiki.gentoo.org/wiki/Fontconfig
https://en.wikibooks.org/wiki/Guide_to_X11/Fonts
http://www.math.utah.edu/~beebe/fonts/X-...fonts.html
https://www.freebsd.org/doc/handbook/x-fonts.html
https://www.freedesktop.org/wiki/Software/fontconfig/
http://www.yolinux.com/TUTORIALS/LinuxListOfFonts.html
http://unix.stackexchange.com/questions/...-font-file
https://bbs.archlinux.org/viewtopic.php?pid=923075
https://en.wikipedia.org/wiki/Xrdb
https://eev.ee/blog/2015/05/20/i-stared-...ack-at-me/

- Tips:
https://wiki.archlinux.org/index.php/Jav...ment_fonts
https://wiki.archlinux.org/index.php/Met...ible_fonts

- Creating fonts:
https://fontforge.github.io/en-US/
http://www.makeuseof.com/tag/everything-...onts-free/
https://superdevresources.com/create-your-own-font/
http://www.unifont.org/unicodeprimer/

- Typography:
https://en.wikipedia.org/wiki/List_of_typefaces
https://en.wikipedia.org/wiki/Sans-serif
https://en.wikipedia.org/wiki/Serif
http://www.happytypings.com/alphabet/
https://www.fonts.com/content/learning/fontology
http://www.noupe.com/essentials/icons-fo...-type.html
https://wiki.archlinux.org/index.php/Met...ible_fonts


If you want to contribute check this thread.


Music:
Owen Lowery - Dream On Instrumental
https://owenlowery.bandcamp.com/
venam
--(Transcript)--
# Fonts on Unix #


# Intro


Understanding how the fonts work on Unix isn't simple.

I had never thought when starting this research that this field was
this deep.

Not only is it overwhelming, but the information around the subject is
also not easily digestable.

The last two weeks I've been researching this and in this podcast
you'll barely find but the essential. It's still skimming the surface
of the topic.

If I explain something in a wrong manner be sure to correct me in the
extended podcast discussion thread.

The people that truly understand the full font stack can be counted on
one's hand, I'd like to salute those true heroes.

They deserve respect.

And if they had an anthem I would've played it at the beginning of
this episode.

So yes, we're going to discuss fonts.


# What are fonts #


Text is made up of sentences and sentences are made up of words, which
are made of characters.

Written text is our primary mean of communication in computers and we
need a way to represent this on our machine and that's what fonts are.

When X11 clients or more generally anything wants to draw text on the
screen they use fonts files, which are files that contain the set of
glyphs, characters, or symbols, or numerals, and rules that are used to
know how to draw that font.


# Let's think #


Let's first stop and think for a moment, how would you write a software
that draws text on the screen?

A benign algorithm would go like this:

1. Have a file with the list of characters and their pixel representation.
2. Place the pen to the cursor position.
3. Load the glyph image.
4. Translate the glyph to the origin of the pen position.
5. Render the glyph to the target device.
6. Increment the pen position by the glyph's advance width (in pixels).
7. Start over again at step 3.

However, it's not as simple as that...

What about right to left writing. What about languages that need to
reshape their characters differently depending on what it's followed
or preceded by. What about spacing between letters that also varies.
What about making the text clearer instead of blocky by only fitting
the pixel space. What about resizing the text size?

So many ifs...


# Fonts in the TTY #


The method of laying text on the screen we just mentioned is not far
from the truth when it comes to TTYs.

The virtual console is handled by the console driver, and it's that
driver that has the role of drawing the text.

Configuring those drivers differs between the different type of Unix-like OS.

FreeBSD for example comes with no fonts in the kernel but loads the
default font from the console driver or vt or syscons while Linux,
netbsd, and openbsd have a default fonts inside their kernels.

In most Unix-like OS Those fonts can be changed through configurations.

Generically the process unfolds like this:

There's a keymaps for the console that connects the keyboard layout
currently configured with the keypressed.

For instance on Linux that keymaps is changed in `/usr/share/kbd/keymaps/`.

At this point we can know which character is requested.

Now we have to get what we want to display from the font structure or file.

The format of the console fonts are just hex values for the pixels
representation of every characters. They are fixed in size usually 8x16
pixels and monospaced, which makes them very simple. More or less literal
bitmap representations of characters.

Ok, so we got a pixel representation of our character, let's display it.

To do that we have to use the video graphics array framebuffer, the
VGA framebuffer, which is a standard working on virtually all post-90s
graphic cards that let you directly display things on the screen. But
those also work on CGA, EGA, MDA.

However there's a condition here, the console fonts are limited to
256 glyphs and if they want to double to 512 for unicode fonts they to
reduce the colors used from 16 to 8, the 8 other colors are originally
used to display brighter versions of the first 8, so that the extra bits
are used for the extra characters association.

This translation is encoded inside the unicode font file in a translation
table called the unimap.

Once that's all set the console can send those bits to the framebuffer
and they are displayed, the position of drawing then moves where the
cursor is.

> The text buffer is a part of VGA memory which describes the content of
> a text screen in terms of code points and character attributes.

This is sort of similar to our first guess as to how a character would
be displayed on the screen, just a notch more difficult and constrained.

The constraint of 512 glyphs can be omitted through a framebuffer
translation layer but we won't discuss it here.

Let's discuss font extensions and formats in the console.

As far as the BSDs goes it highly depends on which flavor you are using.

- For Open and Net BSD the font format is wscons.
Hardcoded in the kernel
- For Linux the format supported are psf (PC Screen Fonts) and psfu for
unicode fonts.
located in `/usr/share/consolefonts`
- For FreeBSD the font supported depend on the console driver:
- for the syscons the format is the .fnt
located in `/usr/share/syscons/fonts/*.fonts`
- for the vt aka Newcons the format supported is the hex fonts,
note that this supports unicode while the later doesn't
The fonts are set manually, not necessarily located anywhere.


The common thing between all those formats is that they are bitmaps and
thus easily editable and convertable from one to another.

There are tools to convert from bdf format to wscons.
From bdf to HEX format.
Many psftools, such as otf2bdf.

You can even show those bitmaps directly on the screen using a tool
called raw psf.

And if you were wondering, BDF stands for Glyph Bitmap Distribution
Format, which is exactly what we want, another bitmap font format.

Now the specific configuration and how to set the fonts and keyboard
translation are specific to the Unix-flavor and I won't list the commands
themselves. You can easily refer to the show notes for that.

For instance `showconsolefont` on Linux display a preview of all the
glyphs in the current font.


# Unicode what? locale? #


We rather often hear about locales and unicode that we need to set when
installing a new Unix-like OS on a machine.

What are those? Do they have a relation to fonts?

Let's read a nice definition that clarifies this:

> A locale is a set of language and cultural rules. These cover aspects
> such as language for messages, different character sets, lexicographic
> conventions, and so on. A program needs to be able to determine its
> locale and act accordingly to be portable to different cultures.

So locale could be used to specify anything that varies from one culture
to another and whichever program can choose to respect them.

So what does this have to do with anything we've said so far?

Well, there's a relation to the keyboard translation table, remember
that first part that translates whatever key you press into characters.

This is dependant on culture, for instance if you have an AZERTY keyboard
you need to set that in the locale, the VC Keymap.

But it doesn't stop there, text is language and language varies by locale.

On a lower level, locale works by changing the behavior of many functions
inside the C library, for instance isupper, toupper, strftime, etc..

You could disply the time in a 24h format instead of the 12h one.

All change according to your preferences.

It also changes the default language for output of many programs, for
example manpages.

There was a time where one would need to input, render, print, search,
spell-check, all in one language at a time. A single character set for
every locale. Now with the adoption of Unicode, 8 bits or multibytes
instead of 7bits, as the canonical character set we don't have to do
that anymore.

It's all languages all the time.

The command you have to remember about locale is `locale`.

So in conclusion, locales don't really have anything directly related
to fonts.


# Different types of font, extensions #


When moving a layer up, in the graphical land there's more room for
flexibility with fonts.

There are two generic categories of font formats, either bitmap fonts,
just like the ones we discussed earlier, consisting of a matrix of
dots or pixels representing each glyphs, or outline or vector fonts,
consisting of bezier curves, drawing instructions, and mathematical
formulae to describe each glyphs, making them scalable.

For instance the extensions we mentioned earlier pcf, bdf, wscons,
etc.. are bitmap formats while extensions like otf, ttf, and pfa are
outline formats.

There are many font extensions which follow different formats falling
in either one of the category, bitmap or outline, you can find a list
of them in a link in the show notes.

A font itself is a family or also called a typeface, for instance the
font Vera Sans is a typeface. The typeface can divide up into different
versions of that font, one could be bold, another italic, another serif,
another monospace, etc..

We'll come back later to discuss what is inside some of those files and
how to manage them.


# Generic overview #


We've seen how text is layed on the screen when using the TTY but what
about the graphical environment, how is it rendered there?

Starting from bottom up here's how it goes:

- At the complete bottom of the stack the display server receives some
shapes to draw.

- A library is used to send the appropriate glyphs to the display server
doing some adjustments before sending it when appropriate.

- A library is used to load the font from the font file and rasterize it,
that is converting it to a bitmap if it's not already. It can also add
hinting and anti-aliasing which we'll discuss in a bit.

- A font layout and shaping engine keeping track of where to lay down
everything and how, figuring out the complex rules for the font and
language in use. It's a sort of state machine for the glyphs

- A software responsible for managing the fonts, configuring what kind
of adjustments need to be made on them, knowing their location and
searching for them.

- A software requesting some text to be drawn on the screen.

Don't worry about most of the details here, just try to grasp that
there are different softwares layed upon each others doing different
tasks. We're going to name the different softwares later on and explain
in depth what they do but you'll need that little overview to make it
easier to understand.


# The problem with fonts on screens #


Ok, so that's a very generic overview of how things should happen to
draw text in a graphical environment.

Before continuing we need to take a little detour to explain something.

We went into the details of how to display bitmap fonts but what about
vector/outline fonts, which most of the graphical fonts are?

The process of converting text from a vector description to a raster or
bitmap description is called font rasterization. This also involves doing
some graphical operations to make the text easier to read, to optimize
rendering it, like anti-aliasing and hinting.

But why do we need that?

And what does hinting and anti-aliasing do?

The problem emerges from the fact that we're using pixelized screens,
it all comes down to the resolution of that screen, the number of dots
per inch, DPI.

Fonts are not mesured in dpi however, they are mesured using another
metric, the points, so that irrespective of the output device they'll
keep the same physical dimension.

And thus, it would mean that the higher the DPI the cleaner the drawing
of that glyph would appear and the lower the DPI the more distorted the
glyph would appear.

It's not unusual for printers to have a DPI going from 300 to 500 while
most of today's LCD screens have a DPI around 96, which is insufficient
for accurate rasterisation.

And because all problems need a solution, we certainly have one or many.

Let's discuss three of them.


* Font Hinting


Font hinting aka grid fitting is a technique that modifies the shape of
the glyph so that its ensured to line up with the rasterisation grid,
in the case of LCD it means lining it up with the pixels.

That gives a more consistent text than the un-hinted counterpart however
this consistency comes at the price of accuracy, hinted text doesn't
have the same shape that was intended by the font creator.

However hinting is a great way to make small text readable on low
resolution devices.

There are many "levels" of hinting and hinting can happen at different
layers in the font rendering stack.

For example the hinting rules can be embedded inside the font file or
it can be automatically done by some library along the way without any
rules implied.

N.B.: Until May 2010 TrueType bytecode hinting was patent encumbered
by Apple.


* Anti-aliasing


Anti-aliasing is a technique that uses the property of a pixels being able
to display shades of colors, instead of full blown red or green or blue,
to create a blur signal around the glyph to reduce it's maximal frequency.

In layman's term anti-aliasing means to avoid aliasing, which in the
signal processing world means the effect that causes different signals
to become indistinguishable, which in our case means that because we
have low dpi many details are contained within a single pixel and thus
are indistinguishable. And to do that we create a ghostly effect that
creates back the details.

This does a good job at preserving the shape and aspect of the glyph
but at the cost of clarity because anti-aliased text is made of much
lower contrast.

As opposed to hinting, anti-aliasing can't be embedded in fonts and is
usually done at another layer.


* Combining Anti-aliasing With Hinting


Now the question is: Can we combine those and would we get better results?

The answer is that it depends on the order of how they are applied.

If hinting is done on an already anti-aliased text it'll consider the
ghost applied around the glyph and also apply hinting to it, which might
deform the text even more.

This is particularly an issue if the hinting is embedded inside the
font file and is applied directly by the layer that is responsible of
the reading and handling the font files.

The solution to this is to apply hinting and anti-alias at another
layer and not in the font and only to use slight hinting and not full
blown aggressive hinting.


* Sub-pixel Rendering


Sub-pixel rendering is a technique or more of a hack that uses a property
of LCD or OLED screen pixels to make it appear as if the resolution of
the display is higher than what it is.

A pixel is composed of multiple sub pixels, it might be 3 sub-pixels,
one for red, one for green, one for blue. Those pixels are arranged and
layed in a fixed order for the same screen, so for instance a pixel has
the red,green,blue sub-pixels layed out horizontally in that order from
left to right.

The way sub-pixel rendering increases the resolution of the screen is by
playing around with those sub-pixels in a way similar to anti-aliasing
but at a smaller level combining this with the fact that our eyes have
difficulties finding differences between the sub-pixels colors when they
are using small intensities.

Imagine it as considering sub-pixels as if they were whole pixels,
though it's not really that.

There's an excellent link in the show notes showing in details how this
work if you want more information on that topic.

There are two drawbacks.

The first one is that it only works with displays that use technology
similar to pixels.

The second drawback is that sometimes you can notice the colors of the
subpixels with your eyes. That is an effect called color fringing,
seeing the sub-pixel color on the fringe of the glyph. It is due to
bad filtering such as sub-pixel rendering not regulating correctly
the intensity of the sub-pixels. It can be countered by using a better
filtering to normalise the difference between adjacent sub-pixels.

N.B.: Microsoft has several patents on subpixel rendering technology
and thus it's disable by default in some free software rendering tech
such as FreeType.


* Subjectivity of fonts


So those are techniques to make or try to make the font look better. But
"better" is a subjective word.

One relevant example is when Apple first released their Safari browser
for Windows in 2007.

While doing that they bundled with the browser their font rasteriser
which gave the opportunity for people to judge which approach font
rasterising they found better.

Multiple bloggers commented on this subject, some liking it, while most
didn't. But overall there was no real way of knowing which one was better
suited at its job. Both did what they were intended to do.

Windows users prefer Microsoft's system and Apple users prefer Apple's
system.

The moral of the story is that consistency between font rendering within
one OS is the key.


# The Stack #


Now that we know the challenges of font rasterisation we can finally
discuss the real software stack that sits on a free Unix system.

We'll discard Apple but you can still read about it in the show notes.

Let's just say that It uses Quartz for rendering on the screen, it's
the graphic engine, and take the approach of not forcing glyphs into
exact pixel position, so no hinting at all, not even the hinting found
inside the font file itself. Instead it uses a combination of anti-alias,
sub-pixel rendering, and sub-pixel positioning. The rasterisation and
layout takes place inside the AAT, Apple Advanced Typography.

That's all we'll say.

So on other Unix-like OS, what's the stack?

The answer is somewhat non binary, it's not straight forward because as
with everything in the free Unix world there are many options to achieve
the same goal.

The result is a collection of separate modules sitting on top of each
others each influencing the rasterisation process.

At the very bottom of the stack we have the graphical stuffs, the things
that handle directly drawing on the screen.

This is usually the display server, X11 or a Wayland compositor.

It receives the shapes from somewhere and draws them, that's its job.

X11 has the X render extension that provides basic support for caching
client side rendered glyphs shapes, so that they aren't recomputed.

Now moving up we get the piece responsible for interacting with the
display server, the piece that uploads the image that we want to render.

Some times ago this piece was directly incorporated inside X11 and so
the RENDER extension we just talked about didn't need to exist either.

Well, it's still there and can still be used, so we can't talk in a
past tense.

It's regarded as the older server side font handling and referred to as
the Core X font subsystem.

When it's used the X server handles the rendering, and loading of the font.

It loads and stores each character inside the X server and so the font
is accessible to anyone that is connected to it, it draws them upright.

However, it doesn't support nor antialiasing nor subpixel rasterisation
and you have to use a weird notation called XLFD, X Logical Font
Description to specify which font you want to use. Moreover it's only
recently that it started to support scalable font as it only supported
bitmap fonts before.

Utilities such as `xfontsel` and `xlsfont` help you choose the
configuration for the XLFD and the font locations need to be hardcoded
in an X11 configuration file by adding values to the FontPath directives
or by running the `xset fp` command.

So in that scenario the X server does all the heavy work.

But it is not very flexible and doesn't render smooth fonts so things
slowly got decoupled and let the handling of fonts to be done by clients
instead and that's where the RENDER extension we talked about was born.

As with everything graphic you need a layer that would be used to send
the glyphs and handle the graphical side.

Other than the Xlib and XCB that are used for the communication with X11
we have, as with any X application, libraries that deal with optimizing
the rendering for specific video hardware and output formats.

For instance the Cairo library is optimized for 2D graphics, SDL too,
OpenGL for 3D, etc..

Namely the most used libraries to interact with the X RENDER extension
are Xft, the semi-obsolete generic replacement of the X Core font,
Cairo for the GNOME stack, Qt for the KDE stack.

That resolves sending the glyph to the X server but we still got a lot of
things to do, we have to get the font, load it, rasterize it, clean it,
customize it, etc..

Xft, Cairo, and Qt, other than interacting with the X RENDER extension
act as interfaces to the Freetype font rasteriser.

They sit in the middle.

FreeType is the most popular font rasteriser library on Free Unixes,
it's small, efficient, highly customizable, portable, and under two free
licenses, a BSD-like one and a GPL one.

FreeType has the widest range of supported font formats in the world.

Thus it's used in a lot of places like the Android operating system,
the playstation, Apple uses it next to its AAT in iOS and macOS, and
it's used in the OpenJDK platform.

As we've discussed, rasterising is the process of rendering text into
bitmaps and using some techniques to make the text clearer on the screen.

FreeType provides that easy to use and uniform interface to load and
access the content of font files and get back a nice bitmap of the
glyph requested.

FreeType provides a way to tell it to activate auto-hinting, TrueType
bytecode hinting, which is the embeded font hinting, antialias, sub-pixel
rendering, etc..

It does all we mentioned earlier if we ask it to.

So to recap so far we have that:

A have a graphic handling layer sitting between the X RENDER extension
and FreeType, which is the font rasteriser.

One thing that needs to be mentioned is that some of those libraries
sitting in the middle apply some fancy changes to the glyph themselves
before sending it rather than having FreeType doing it.

For instance, Cairo can do sub-pixel rendering and filtering itself,
Qt falls back to a FIR filter when FreeType doesn't offer filtering,
and Xft offers some intra-pixel filtering.

That's cool, now we need something that will tell FreeType which font to
load, to select and what kind of pretty changes it needs to apply to it.

That's a job for a font configuration engine that goes by the name
of Fontconfig.

The job of Fontconfig is to provide an interface for font discovery and
configuration, such as if hinting is activated for a specific font or not.

One of its job is to always match a font whenever the case, if the
current font doesn't support a character it should transparently fall
back to another font if possible.

And it supports utf-8 all the way so it always yield reasonable results.

Its font selection mechanism is very convenient and expressive, it let
users match fonts according to patterns and characteristics such as if
the font is slanted, bold, its size, etc..

We'll discuss Fontconfig specifics in one of the next section.

At this point we've got rendering, rasterising, and font selection and
configuration, you would think that this would be enough but the font
stack doesn't end here.

There's yet another layer if you remember correctly and that is the font
layout engine.

They are FriBidi, HarfBuzz, ICU, m17n, and SIL Graphite.

Those engine are mainly used to support internationalization, as in
multiple different languages with different shaping and layout rules.

Let's only discuss one of them, HarfBuzz.

It sits on top of FreeType as an OpenType Layout engine, opentype being
the de-facto font format that support complex text rendering on Free Unix.

It's the library that actually understands the sophisticated features
inside the font. It keeps track in a sort of state machine of the glyphs
that need to be drawn, rearranged, reshaped, inserted, in different
situations and contexts.

It's context sensitive.

Without a layout engine you wouldn't be able to type correctly in certain
languages because they aren't a one to one mapping between the character
you enter and the glyph that appear.

Simply said it takes complex unicode text and spurts out the right
glyph indices and right position where they should appear taking in
consideration the whole string.


Now finally the font stack is complete.

Atop of this stack there are even more abstraction layers such as Pango
which is like a roof supporting different sorts of font layout backends.

For instance Pango is used in GTK and it regroups Cairo or Xft plus
FontConfig for the font configuration and HarfBuzz as a layout engine.

But Pango doesn't stop there, it's multi-platform.


# The font files, format and information #


Finally, we got a bit of an understanding of this russian doll.

Now we can take a bit of time to explore what's inside some of the
font files.

Let's first name some of the formats that are supported by FreeType:

* TrueType fonts (TTF) and TrueType collections (TTC)
* CFF fonts
* WOFF fonts
* OpenType fonts (OTF, both TrueType and CFF variants) and OpenType collections (OTC)
* Type 1 fonts (PFA and PFB)
* CID-keyed Type 1 fonts
* SFNT-based bitmap fonts, including color Emoji
* X11 PCF fonts
* Windows FNT fonts
* BDF fonts (including anti-aliased ones)
* PFR fonts
* Type 42 fonts (limited support)

N.B.: TrueType and OpenType are mostly identical even some fonts with
a ttf extension are actually OpenType fonts.

Let's revisit our definition of what a font is.

> A font is a collection of various character images that can be used to
> display or print text. The images in a single font share some common
> properties, including look, style, serifs, etc. Typographically speaking,
> one has to distinguish between a font family and its multiple font faces,
> which usually differ in style though come from the same template.

In some cases the whole font family can be represented by multiple
files where each file represent a different face of the font. In some
other cases all the faces of the font are included in the same file,
which we call a font collection file.

And thus a single font file might in fact just be a single font face of
a font family.

Those files may contain character images named glyphs, character metrics,
information regarding the layout of the text and processing of specific
character encodings.

It's important to note that a single character can have several distinct
images, as in different glyphs that can be used depending on the context.

There are also cases where multiple characters joined together can form
a single glyph.

This relationship between characters and glyphs is complex and that's
what the layout engine we talked about handle.

Each glyph has an index, and the font file contains a table called the
character maps which is used to convert character codes for a given
encoding. There can be multiple charmaps per fonts.

Remember when we said that the layout engine job was to handle which
correct glyph index was to be returned in what situation.

Also associated with the glyphs there are various metrics to describe
how and where to place and render the text, and how much point should
the cursor advance forward after the text insertion.

Metrics are extremely important for the text flow.

And remember that all the metrics are expressed in points and not in
pixels, expept for bitmap font formats.

And that's what's contained in a font file.


# How are they managed #


Let's return to the management part of the fonts, the part that Fontconfig
takes care of.

Fontconfig provides many utilities all starting with the prefix `fc-`.

For instance:

```
fc-list #lists all fonts available and cataloged for usage in X11 programs
fc-query #to query font files
fc-match #to try to match an available font or alias used to describe the font
```

Fontconfig by default track down the fonts inside certain default
directories such as /usr/share/fonts and ~/.local/share/fonts. It'll
traverse them recursively looking for all available fonts in them.

Fontconfig uses XML files in the /etc/fonts directory to generate its
own internal configs. By default it parses /etc/fonts/fonts.conf which
sets the some default options such as the default directories to read
font from we just mentioned. There are also the equivalent for local
user configuration which take precedence over the global ones.

The /etc/fonts also contains a conf.d sub directory that has additional
configuration files covering different aspect of fontconfig. These files
start with a number indicating the order in which they are executed.

Now you might remember the time I mentioned that hinting was only great
when it was done before antialiasing, well, that's where you choose the
order of things.

Usually distributions offer some presets files and you symlink them
inside that directory, as it's very tedious to create your own.

For example, to enable sub-pixel RGB rendering globally:

```
cd /etc/fonts/conf.d
ln -s ../conf.avail/10-sub-pixel-rgb.conf
```

In those files you can also pinpoint how the fallback mechanism will
take place and change it.

I won't cover all the different things that can be in those xml files
but again, there are links in the show notes discussing this in details
and you can also refer to the fonts-conf man page which is not bad at all.

To find out what settings, fallbacks, etc.. are in effect for a font
you can use:

```
fc-match --verbose 'some font'
```

Now how do we go about installing a font.

1. Simple we download the font we want in a format supported by FreeType.
2. We move the font to a directory managed by Fontconfig and make sure
its readable.
3. Update the Fontconfig cache by running `fc-cache`.

That's it!

Remember that for the X core fonts you have to do that at the X server
level and it's not as simple.

You'd have to mark the directory as a X core font dir and then tell the
X server to consider using them:

```
mkfontscale $dir
mkfontdir $dir
xset +fg $dir
xset fp rehash # Forces a new rescan
```

Or instead of all that hassle you can rely on your package manager.


# Don't forget some commands #


Let's name some useful commands related to fonts.

```
xrdb - the xresources database, some fonts can be set there for some
applications
xfontsel - point and click selection of X11 font names
showfont - font dumper for X font server
xlsfonts - List all the fonts on your system
fslsfonts - List fonts served by X font server
mkfontdir - create an index of X font files in a directory
fsinfo - X font server information utility
fstobdf - generate BDF font from X font server
xfd - display all the characters in an X font
chkfontpath - simple interface for adding, removing, and listing directories in the X font server's path
TrueTypeViewer – a free, powerful OpenType viewing tool with a TrueType
instructions debugger (not using FreeType)
```

There are some gnome configuration tools such as:
```
gnome-font-properties
gnome-font-viewer
gtkfontsel
```

Notably there are all the Fontconfig tools we mentioned before `fc-`.

There are utilities to convert from one font type to another.
```
dxfc
bdftopcf
bdftosnf
mftobdf
fstobdf
```

Utilities to edit bdf, bitmap fonts:
```
bdfresize - a bdf font resizer
xmbdfed - a bdf font editor
```

To view some otf or ttf fonts you can even use a web interface, some
websites offer that.

You can use image magick to display all the characters inside a font by
issuing the `dipslay` command:

```
display fontname.ttf #part of imagemagick
```

Some utilities like `Fontmanager` and `fontmatrix` lets you organize
groups of fonts to be installed or uninstalled, and you can preview them
and see their features, whether installed or not.


The last utilities to mention are the utilities that can manipulate
the settings of the xserver itself, the ones stored in the XSETTINGS
specification.


# Tips #


Here are some tips.

There's something called Infinality that regroups a set of patches
for FreeType with a bunch of preset for Fontconfig. It is said to show
higher quality rendering but as we've said earlier that definition is
somewhat subjective.

---

The JRE, Java Runtime Environment fonts are harder to configure you have
to set some environment variable so that they respect the antialias and
hinting you want.

So next time don't rage when you see ugly font inside a java application
and go set those up.

---

Fonts are not limited to text, a lot of fonts are emogi or pictographic
fonts.

They are widely used around the internet as icons sets and is also used
a lot in the ricing community to decorate bars.

---

If you're falling short on Unicode fonts there's a link in the show
notes that regroup many great libre open source fonts in all languages.

It's called unifont.org

http://unifont.org/fontguide/

---

There are fonts that are metric-compatible together.

It means that their metrics match, and as you remember the metrics are
everything related to the size of the glyphs. Those fonts when they have
the same face can be used interchangeably as replaceable fonts without
changing too much the aspect of the text.

Remember that in your next web project when you want to provide fallback.


# Making your own font #


Let's discuss making your own font and typography.

To make your own font you don't truly have to be an expert typograph
but having some knowledge could help.

The world of typography is freaking huge and that's not a surprise,
writing has existed for a long time and it's obvious that there would
be a domain of expertise being built around it.

If someone claims they "know" typography it's probably just that they
have a vague idea of some concepts. You must be a graphic designer or
someone who has a background in this field to be versed in the art of
typography. I'm not one of those.

I had thought about including a section in this podcast about typography
but I was too overwhelmed.

Nevertheless, I've linked resources in the show notes that could get
you started if you wish to.

Now back on topic, if you want to create or edit a font on Unix there's
a software called fontforge.

It's a very advanced software with all the features you'll ever need.

On their official website they have a book called "Design With Fontforge"
which seems like a wonderful book. It goes through all the steps needed
to understand what fonts are, typography, the vocabulary, the anatomy
of glyphs, and how to design a font.

Yep, glyphs even have their own anatomy...


# Conclusion #


As I've said in the beginning of this podcast, fonts are a deep topic and
so I encourage you to read from the links I've added in the show notes.

What enraged me when starting this research was that there was no clear
document discussing the font stack of current Unix-like operating systems.

I truly hope this podcast enlightened you as much as researching for it
did for me and that I haven't messed up any info.

Yep.

Those are the fonts!
sametsisartenep
Thanks for this post, venam. I'll bookmark this so I can get into the internals in a future, at least in the Xft realm and rasterisation.




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