0:00:06.280,0:00:09.300
Okay, good morning everyone.

0:00:09.300,0:00:12.540
I'm going to talk about the[br]Linux Font Rendering stack,

0:00:12.860,0:00:18.680
and that is what I learned the last[br]four and a half years.

0:00:18.680,0:00:22.080
I worked at the[br]city administration of Munich.

0:00:22.920,0:00:28.400
For introduction to font rendering,

0:00:30.320,0:00:34.780
I can say writing is[br]the most used interface,

0:00:34.780,0:00:39.080
or probably the most used interface[br]between humans and the machines.

0:00:39.080,0:00:45.700
So all of you probably use it everyday[br]on your computer.

0:00:48.500,0:00:52.780
Screen text is replacing text on paper[br]more and more

0:00:52.780,0:00:56.820
and this is still an ongoing process.

0:01:00.620,0:01:09.160
The way from a string in a computer to[br]display text is surprisingly complex,

0:01:09.160,0:01:14.640
And writing in itself is quite profound.

0:01:14.640,0:01:24.960
For example, it's influenced by history[br]so probably all, or at least most,

0:01:24.960,0:01:30.680
writing systems are derived from some[br]pictograph writing systems.

0:01:31.140,0:01:34.440
This is also true for Roman letters.

0:01:36.080,0:01:43.980
And also the Roman letters themselves,[br]they changed a lot since 2000 years ago.

0:01:43.980,0:01:51.120
In the Roman Empire they used some[br]different letters than we use now.

0:01:51.120,0:01:56.980
So the goal of this talk is to raise[br]awareness of font rendering in computing,

0:01:56.980,0:02:00.740
with the focus on the Linux desktop.

0:02:04.740,0:02:11.680
Now to the history,[br]and then I talk about typography.

0:02:13.780,0:02:17.280
Text display in early computing.

0:02:17.380,0:02:24.760
In early computing it was just[br]a way to display results.

0:02:26.380,0:02:29.900
Before that there were[br]only flashing lights

0:02:29.900,0:02:34.420
where you can read the results[br]and...

0:02:35.660,0:02:39.840
[audience member] ??... BT100[br]?? raise your hand

0:02:43.300,0:02:47.660
[Max] And the output device receives[br]a page or a character stream,

0:02:47.660,0:02:52.000
and then the presentation is the job[br]of the output device.

0:02:52.000,0:02:58.000
So for example, a typewriter[br]or a printer or a terminal.

0:02:58.000,0:03:05.780
And this is a BT100[br]you can see on the right side.

0:03:05.780,0:03:08.340
So this is a real terminal.

0:03:13.260,0:03:19.420
But going on in history[br]there's the home computer era.

0:03:21.860,0:03:25.460
In the home computer era you have[br]fixed character sets

0:03:25.740,0:03:31.840
and most of the time due to system[br]limitations, memory limitations,

0:03:31.840,0:03:35.700
you have graphics mode and text mode.

0:03:38.100,0:03:46.840
In the graphics mode you can basically[br]set the pixels more or less as you want,

0:03:46.840,0:03:53.000
and in the text mode you can use fonts.

0:03:55.620,0:03:59.540
The screen configuration at that time[br]is more or less defined

0:03:59.540,0:04:01.540
by the state of technology.

0:04:01.540,0:04:07.740
So every screen at that time has more or[br]less the same resolution,

0:04:07.740,0:04:15.680
and that's something that the engineers[br]of that time relied on,

0:04:15.680,0:04:18.200
and also software engineers relied on.

0:04:19.660,0:04:24.980
The text rendering was just[br]using bitmap fonts.

0:04:24.980,0:04:37.120
That means you have a fixed size character[br]and you just define it pixelwise

0:04:38.780,0:04:45.040
so it's some kind of hand-crafted[br]characters.

0:04:45.040,0:04:51.320
You have a given raster and then[br]you really display

0:04:51.320,0:04:54.340
these hard-defined characters.

0:04:59.520,0:05:06.740
So then I need to introduce a few[br]typography terms.

0:05:12.380,0:05:16.260
First, there's glyph or a character.

0:05:21.320,0:05:25.420
That's...well you can say a symbol.

0:05:26.920,0:05:31.700
So I think most people can understand what[br]that means.

0:05:31.700,0:05:36.240
Then a font, this is a set of glyphs.

0:05:38.040,0:05:45.320
And then we have a collection of fonts,[br]that is called typeface or font family.

0:05:45.320,0:05:53.020
Those are closely related fonts with[br]the same visual appearance,

0:05:53.020,0:05:59.920
And they differ only in slopes or widths[br]or weights for example.

0:06:03.880,0:06:12.480
Usually with typesetting, with moving[br]letters in the printing press,

0:06:12.480,0:06:25.140
you really had, for weight for example,[br]different pieces/letters/hardware.

0:06:27.740,0:06:31.460
And then the point size,[br]or typographic unit.

0:06:32.560,0:06:41.780
This is a measure of the size, and[br]derives directly from the printing press

0:06:42.560,0:06:44.560
with moving letters.

0:06:48.400,0:06:56.500
There are different definitions, and what[br]we probably all use as point size is the

0:06:56.500,0:07:03.760
DTP point – desktop publishing point,

0:07:03.760,0:07:18.520
where one point is defined as 1/72 inch,[br]which is 0.3527 period millimeters.

0:07:18.520,0:07:25.980
It is interesting to note that this has[br]nothing to do with pixels.

0:07:28.600,0:07:30.980
[question] (unintelligible question)

0:07:30.980,0:07:34.700
[Max] Please use the microphone[br]if you a question.

0:07:35.900,0:07:39.440
[question] ...3257, what's the bar[br]over the 7 mean?

0:07:39.440,0:07:43.160
[Max] It means that the 7 goes[br]on and on and on forever.

0:07:51.000,0:07:58.500
So this is typography of the[br]Latin alphabet...terminology.

0:07:58.500,0:08:01.740
There's something called kerning.

0:08:02.400,0:08:08.380
You can see an example of kerning[br]on the right side.

0:08:08.380,0:08:19.180
So in the printing press you have letters[br]and they usually have a gap.

0:08:21.400,0:08:29.600
To improve the readability, and to[br]make all the text appear more uniform

0:08:31.140,0:08:33.760
the typesetter reduces the gap.

0:08:35.659,0:08:39.700
With moving letters they have special[br]letter pairs...

0:08:40.679,0:08:46.060
if you go on with this[br]there are ligatures,

0:08:46.140,0:08:50.620
which are replacement glyphs for close[br]standing characters.

0:08:52.140,0:08:57.300
An example of this is a double f, fi or fl.

0:08:58.300,0:09:05.440
So you can see also in the slides here[br]that double f is such a ligature.

0:09:06.320,0:09:08.600
It's one connected glyph.

0:09:10.980,0:09:16.480
And then there's a speciality[br]if you reverse all of the ?? [static].

0:09:18.120,0:09:20.040
The term non-proportional font.

0:09:20.040,0:09:27.300
So you have a font where very character,[br]every glyph, has the same width.

0:09:27.300,0:09:30.640
This is also called monospace font.

0:09:33.640,0:09:40.820
Sometimes you distinguish half-width[br]and full width letters.

0:09:41.480,0:09:45.740
This is also something you would see[br]on a typewriter for example.

0:09:47.440,0:09:54.020
Early bitmap fonts are usually[br]monospaced fonts.

0:09:56.440,0:10:01.740
Okay, let's go to[br]the text rendering stack.

0:10:06.520,0:10:08.980
Text rendering today.

0:10:10.400,0:10:15.060
In all computing nowadays,[br]typography is introduced.

0:10:15.080,0:10:24.500
So won't find many devices on the market[br]which don't use accurate typography.

0:10:28.160,0:10:32.280
Glyphs are now represented as[br]size-independent outlines.

0:10:32.280,0:10:37.520
We can see on the right side there's[br]a font editor: Font Forge.

0:10:37.520,0:10:41.900
This is the way that such fonts[br]are created.

0:10:41.900,0:10:47.160
So you can see here in the picture[br]the outline of the "S".

0:10:49.200,0:10:55.960
It's a size-independent outline and[br]you can just use that for

0:10:55.960,0:10:59.180
every kind of display.

0:10:59.180,0:11:04.020
And then you do something that is called[br]rasterization, or sampling, or rendering

0:11:04.020,0:11:08.000
for displaying it at the actual display.

0:11:09.660,0:11:13.760
In the past this allowed for new[br]applications for computers.

0:11:13.760,0:11:19.680
First it allowed word processing and[br]computer-based typesetting.

0:11:21.240,0:11:26.320
Before that typesetting was[br]a very hard job.

0:11:26.740,0:11:30.800
It allowed internationalization.

0:11:36.600,0:11:41.500
It allows universal graphical interface[br]which goes

0:11:41.500,0:11:45.420
hand-in-hand with internationalization.

0:11:46.280,0:11:52.380
Come to think of it, not so long ago it[br]was not so common that you could

0:11:52.380,0:11:58.280
buy devices where you can easily switch[br]the language to

0:11:58.280,0:12:01.680
any language you would like.

0:12:01.680,0:12:05.320
This is just a recent development.

0:12:06.600,0:12:15.600
So now I will give you an overview of[br]the formats we see on Linux systems.

0:12:15.600,0:12:18.880
First I talk about the bitmap formats.

0:12:18.880,0:12:27.120
Today we have bitmap formats in the[br]PC Screen Font format,

0:12:27.120,0:12:28.960
PSF or PSFU.

0:12:28.960,0:12:36.180
These are the fonts that are used for the[br]Linux VT, also known as the console.

0:12:36.180,0:12:45.700
Usually you can store in such a font[br]256 or 512 glyphs.

0:12:45.700,0:12:52.540
Some of them contain[br]a Unicode translation table.

0:12:53.800,0:12:59.500
And on the other hand there are[br]X Window System Bitmap Fonts.

0:12:59.500,0:13:02.820
There are three formats:

0:13:02.820,0:13:07.060
There's a Sever normal Format (SNF).

0:13:07.060,0:13:11.340
Glyph Bitmap Distribution Format (BDF).

0:13:11.340,0:13:13.960
And Portable Compiled Format (PCF).

0:13:13.960,0:13:22.680
Nowadays PCF is the only letter that[br]you can find on a Linux system if so,

0:13:22.680,0:13:29.160
and the first two are deprecated.

0:13:29.160,0:13:40.220
And also the X Window Bitmap Fonts[br]themselves are not very common these days.

0:13:44.560,0:13:47.380
To the outline font formats.

0:13:49.020,0:13:51.960
There are Postscript Formats.

0:13:53.920,0:14:05.240
Postscript Formats have different versions[br]as I would call them. It's called types.

0:14:05.240,0:14:11.540
Type 1 is the one that is still relevant,[br]to a certain degree.

0:14:11.540,0:14:16.760
Those are the ones you can probably

0:14:16.760,0:14:21.400
find on a standard Debian installation[br]for example.

0:14:21.400,0:14:23.880
It uses cubic bezier curves.

0:14:26.120,0:14:35.760
The file format is divided into[br]different files.

0:14:35.760,0:14:39.500
So for every font you have[br]Printer Font ASCII

0:14:39.500,0:14:44.200
or a Printer Font Binary file,[br]and you have

0:14:44.200,0:14:49.120
a Print Font Metric or[br]Adobe Font Metric file.

0:14:54.740,0:15:00.900
Then you have the Truetype file format.

0:15:02.860,0:15:07.700
This is more common. I guess everyone[br]heard of that already.

0:15:08.940,0:15:12.140
It uses quadratic bezier curves.

0:15:13.760,0:15:21.420
It can contain optional code for[br]TrueType Hinting Virtual Machine.

0:15:21.420,0:15:25.120
What that means I will explain latter.

0:15:25.120,0:15:30.740
There's a third format,[br]the OpenType format,

0:15:30.740,0:15:35.160
which has two possible glyph formats:[br]one is truetype,

0:15:35.160,0:15:40.980
and the other is Compact Font Format,[br]which is based on Postscript Type 2.

0:15:40.980,0:15:47.880
So you can say what is new in this format,[br]or what's the difference?

0:15:47.880,0:15:51.700
Well it supports so-called Smartfonts.

0:15:53.580,0:15:59.600
That means you can have language-specific[br]ligatures or character substitutions.

0:16:01.360,0:16:09.560
For example, kerning classes, which means[br]you have a class of characters like

0:16:09.560,0:16:13.520
the A and different variations.

0:16:13.520,0:16:19.820
So these are A with different diacritic[br]symbols,

0:16:19.820,0:16:30.560
and you can just use one kerning class for[br]all of those characters and don't have to

0:16:30.560,0:16:37.580
invent the wheel for every A with[br]diacritic symbols anew.

0:16:43.540,0:16:50.140
Now to the font rendering techniques that[br]I use today.

0:16:53.540,0:17:02.360
This only applies to the outline fonts[br]because well rendering bitmap fonts is

0:17:02.360,0:17:11.020
obviously quite easy. You just paint the[br]pixels that are in the bitmap.

0:17:11.020,0:17:17.480
So rasterization is all about using[br]outline fonts.

0:17:19.280,0:17:24.619
The one library library that is used all[br]over the free and open source world

0:17:24.619,0:17:26.180
is FreeType.

0:17:26.180,0:17:40.600
It is used on Linux system, BSD desktops,[br]Android, and ReactOS, and also some others.

0:17:40.600,0:17:47.300
For example it is contained in Ghostscript[br]and therefore in most of the printers.

0:17:49.040,0:17:52.140
It's also on iOS [exhale].

0:17:53.140,0:18:00.860
So the naive rasterization algorithm would[br]be just lay a pixel raster over the outline font,

0:18:00.860,0:18:07.280
over the character you want to display,[br]and if the center of the pixel is inside

0:18:07.280,0:18:09.900
the outline then you[br]set the color to black.

0:18:14.960,0:18:19.340
The problem is the so called[br]aliasing effect.

0:18:19.340,0:18:23.820
This is what you can see[br]in the picture below.

0:18:23.820,0:18:29.760
So those are the same words,[br]rendered at different resolutions.

0:18:29.760,0:18:36.440
The left one has 10x the resolution[br]of the right one.

0:18:38.620,0:18:49.540
You can see that, for example,[br]the 'w' is quite deformed.

0:18:49.540,0:18:55.340
Or the curl of the 'g';[br]there's even a part missing.

0:18:55.340,0:18:59.800
So you have details of the font[br]which are lost,

0:18:59.800,0:19:02.040
and you have artefacts.

0:19:04.240,0:19:11.580
Somehow, especially in the early computing[br]days you wanted to reduce those,

0:19:11.580,0:19:15.480
and therefore you used a technique[br]called hinting.

0:19:15.480,0:19:20.820
This is to avoid such artefacts and[br]improve the readability

0:19:20.820,0:19:22.520
at lower resolutions.

0:19:22.520,0:19:34.660
Therefore the outline adjusted to fit the[br]pixel raster at the rasterization.

0:19:36.900,0:19:41.840
Some of the fonts can contain[br]instructions, the so-called hints

0:19:41.840,0:19:46.020
where the the name comes from.

0:19:51.360,0:19:58.860
You can see in the example here,[br]in the picture above,

0:19:58.860,0:20:07.860
that it's quite a good result.

0:20:07.860,0:20:15.480
This is much more readable[br]than the word above.

0:20:15.480,0:20:22.560
However, with the use of hinting, there[br]are also characteristics of the font lost

0:20:24.200,0:20:27.540
which is obvious because[br]if you change the outline

0:20:27.540,0:20:31.160
then obviously characteristics get lost.

0:20:31.160,0:20:37.260
And especially important for[br]word processing,

0:20:37.260,0:20:39.640
what you see is what you get[br]word processing,

0:20:39.640,0:20:43.680
that the tracking of the font is changed.

0:20:45.920,0:20:49.960
So tracking means the width[br]of single characters.

0:20:49.960,0:20:56.680
The picture below, this is a picture I[br]took from LibreOffice.

0:20:56.680,0:21:05.300
If you have a close look, you can see[br]that the gap between those 'i' characters

0:21:05.300,0:21:07.300
is not always the same.

0:21:08.040,0:21:16.880
But if do word processing, you actually[br]want to have a result which looks the same

0:21:16.880,0:21:18.880
as on the printout.

0:21:20.480,0:21:26.840
So I would recommend not[br]to hint fonts in

0:21:26.840,0:21:29.860
a what you see is what you get[br]word processor.

0:21:33.520,0:21:40.980
If you have a look beyond the backyard,[br]on macOS, there exists no hinting,

0:21:40.980,0:21:45.780
and in the Windows world, hint can't[br]be turned off,

0:21:45.780,0:21:52.320
so this is hardwired in the[br]font rendering of the Windows system.

0:21:56.120,0:22:03.480
Well another approach to improve[br]readability is anti-aliasing

0:22:03.480,0:22:08.400
which applies multisampling.

0:22:08.400,0:22:15.920
So for every pixel you take samples at[br]different spots

0:22:15.920,0:22:22.240
and then you compute from[br]that a gray value,

0:22:22.240,0:22:29.240
which is a measure of how much of the[br]area of the pixel is covered by the glyph.

0:22:33.260,0:22:40.040
On the picture you can see again[br]the simple raster word,

0:22:40.040,0:22:45.840
and then in the middle you see the word[br]with anti-aliasing,

0:22:46.240,0:22:56.000
and below you can see a combination of[br]hinting and antialiasing.

0:22:58.700,0:23:02.860
Suddenly the text becomes very readable[br]also on low resolutions.

0:23:04.740,0:23:12.460
This is what is usually used in[br]computing in the 90s.

0:23:18.440,0:23:23.560
So there is another approach to improve[br]and therefore I have to

0:23:23.560,0:23:27.080
talk a bit about LCD displays.

0:23:27.080,0:23:37.140
So in the picture on the left, above you[br]can see tube monitor pixels and

0:23:37.140,0:23:40.680
on the bottom you can see[br]LCD monitor pixels.

0:23:40.680,0:23:50.400
All of the pixels consist of so-called[br]subpixels with different colors.

0:23:52.160,0:23:55.940
The mixture of the three different colors

0:23:55.940,0:24:01.660
gives them a wide range[br]of different colors.

0:24:04.560,0:24:12.540
With the tube monitors this is not used,[br]but with LCD display

0:24:12.540,0:24:18.680
depending on the[br]configuration of the subpixels

0:24:18.680,0:24:23.320
it can be used to improve improve the[br]resolution in one direction.

0:24:23.320,0:24:29.400
Therefore you have to know how the[br]configuration of the display is.

0:24:29.400,0:24:36.980
So usually, one pixel, which you can see[br]in the picture below right?

0:24:36.980,0:24:40.120
These are the usual computer monitors.

0:24:40.120,0:24:51.860
One pixel consists of a red, green and a[br]blue subpixel in this order.

0:24:51.860,0:24:58.400
But you have to keep in mind, especially[br]with tablets, or smartphones,

0:24:58.400,0:25:05.200
you can rotate the screen, so you have to[br]keep that in mind.

0:25:06.060,0:25:11.280
Also there are other subpixel[br]configurations.

0:25:11.280,0:25:17.880
For example, depending on the technology[br]there can be additional red or green

0:25:17.880,0:25:20.180
or even white subpixels.

0:25:24.180,0:25:30.400
So there are also multiple possibilities[br]of the configuration.

0:25:33.840,0:25:39.500
We can use this configuration as I said[br]to improve the resolution

0:25:39.500,0:25:45.000
and in the usual case[br]this is horizontally.

0:25:45.000,0:25:50.440
You can see on the picture[br]on the left side,

0:25:52.800,0:25:59.400
first there's the naive,[br]simple rendered character,

0:25:59.400,0:26:03.880
then the character[br]just using anti-aliasing,

0:26:03.880,0:26:08.340
and then there's the[br]subpixel rendered character.

0:26:10.060,0:26:16.260
This one is the most readable[br]or most sharp character.

0:26:16.260,0:26:25.100
Not sharp!... but it's most correctly[br]rendered according to the outline font.

0:26:25.960,0:26:31.420
Depending on the technique of the display,

0:26:31.420,0:26:41.340
you can see a color haze[br]around the characters.

0:26:44.080,0:26:49.260
So this happens when the software[br]and the display technology

0:26:49.260,0:26:52.020
don't match each other.

0:26:54.180,0:26:59.320
So this is what you can see[br]on the picture on the right.

0:27:01.340,0:27:07.900
Okay, let's talk about the font rendering[br]software parts in the Linux desktop.

0:27:10.660,0:27:15.340
There's the so-called server-side[br]text rendering.

0:27:16.600,0:27:21.760
So in the X server there's the[br]Core Font subsystem.

0:27:25.040,0:27:31.940
With that, X11 clients can request the[br]server to display a text

0:27:31.940,0:27:36.160
by sending a string via libXfont

0:27:36.160,0:27:45.220
and using the so-called[br]X Logical Font Description (XLFD).

0:27:45.220,0:27:52.920
Here's an example for Adobe Career font,

0:27:52.920,0:28:02.600
then the X server has to then[br]render the text using the font.

0:28:05.980,0:28:10.940
If you imagine a terminal server setup[br]with thin clients,

0:28:10.940,0:28:18.500
then the thin client runs the X server[br]and the terminal server runs the X client

0:28:18.500,0:28:27.620
and every thin client then has to[br]handle the font rendering.

0:28:27.620,0:28:34.520
So I don't know if[br]this is the only reason,

0:28:34.520,0:28:40.880
but nowadays server-side font[br]rendering is not so common.

0:28:40.880,0:28:47.620
Probably not used anymore.

0:28:52.540,0:28:56.160
Now I have to talk first[br]about font management.

0:28:56.160,0:29:01.720
In Linux systems there is[br]a software called fontconfig,

0:29:01.720,0:29:05.280
which manages installed fonts[br]on the system

0:29:05.280,0:29:15.640
and it configures for example how to[br]substitute fonts.

0:29:17.160,0:29:24.280
For example if in a document there's a[br]font to render a text

0:29:24.280,0:29:27.120
and the font is not[br]available on the system

0:29:27.120,0:29:33.860
then in the font config system there can[br]be rules to replace the font

0:29:33.860,0:29:36.640
with a similar font.

0:29:37.380,0:29:41.020
This is heavily used in Linux systems.

0:29:41.020,0:29:47.760
There are also rules for what font to[br]use if the current selected font

0:29:47.760,0:29:51.480
doesn't contain a character[br]you want to display.

0:29:52.940,0:29:59.020
You can see on the picture on the right[br]that this is also used...

0:29:59.020,0:30:01.800
although I have to admit,

0:30:01.800,0:30:07.920
I had to take this picture on a Debian 5.0[br]system in LibreOffice

0:30:07.920,0:30:12.000
because nowadays[br]it works a bit different,

0:30:12.000,0:30:17.780
but this is a good example where[br]you can see that those characters

0:30:17.780,0:30:20.820
come from different fonts actually.

0:30:23.220,0:30:27.920
There's also a command line tool[br]which is quite nice.

0:30:27.920,0:30:29.580
fc-match command line tool.

0:30:29.580,0:30:37.460
So for example if you want to see what is[br]the replacement font for, let's say, Arial

0:30:37.460,0:30:40.960
then you get the output:[br]okay, it's Nimbus Sans.

0:30:44.840,0:30:47.960
And you can also set rendering options,

0:30:47.960,0:30:55.880
which means you can set anti-aliasing[br]or you can turn off hinting.

0:31:00.260,0:31:06.700
Usually these configurations are stored in[br]/etc/fonts

0:31:06.700,0:31:11.800
and there is also a per-user configuration[br]in .config/fontconfig

0:31:11.800,0:31:19.680
and it's in XML file format snippets.

0:31:21.500,0:31:24.920
In the picture you can see an example.

0:31:24.920,0:31:33.020
This is the replacement rule for[br]Carlito and Calibri.

0:31:35.540,0:31:41.540
Carlito is a replacement font for the[br]nowadays often used

0:31:41.540,0:31:44.200
Calibri font from Microsoft.

0:31:45.780,0:31:54.380
So this configuration says the one way,[br]Carlito is the same as Calibri,

0:31:54.380,0:31:56.240
and the other way around.

0:31:56.240,0:31:58.280
This is just an example,

0:31:58.280,0:32:03.940
you can have a look at /etc/fonts[br]and a lot of such snippets.

0:32:07.340,0:32:12.640
It defines how fonts are[br]displayed on the system.

0:32:16.180,0:32:23.720
Another thing, and this is the reason[br]why I had to take the screenshot

0:32:23.720,0:32:29.780
on an older system, there's a piece of[br]software called HarfBuzz.

0:32:29.780,0:32:35.240
HarfBuzz is Persian for OpenType,

0:32:35.240,0:32:41.460
so this software relies on the OpenType[br]font format.

0:32:41.460,0:32:46.400
You can see on the right side[br]the HarfBuzz logo

0:32:46.400,0:32:50.180
that actually says[br]HarfBuzz in Persian.

0:32:53.500,0:32:56.240
Before I talked about ligatures,

0:32:56.240,0:33:02.840
In some languages ligatures are required[br]to render fonts correctly

0:33:02.840,0:33:09.220
and this is an example on the left of[br]Devanagari, which is an Indic script.

0:33:11.720,0:33:17.700
So if you have the first two characters[br]combined then this is the rule

0:33:17.700,0:33:24.500
of how to replace those characters[br]with a third glyph.

0:33:29.480,0:33:34.280
There were early implementations[br]by Qt and Pango

0:33:34.280,0:33:38.740
and those were integrated in HarfBuzz.

0:33:41.140,0:33:44.780
Well those parts are now known as[br]Harfbuzz Old,

0:33:44.780,0:33:50.220
and the current HarfBuzz is a rewrite.

0:33:51.580,0:33:57.020
Nowaday's it's also used for[br]the so-called simple script,

0:33:59.260,0:34:03.660
meaning especially Latin script,

0:34:03.660,0:34:12.060
and is integrated into Qt, GTK,[br]LibreOffice, Firefox, Android, and XETEX.

0:34:12.060,0:34:14.880
This is what I use for the slides here,

0:34:14.880,0:34:20.840
so all the slides here are[br]also rendered using HarfBuzz.

0:34:20.840,0:34:24.880
And of course the whole[br]font rendering stack.

0:34:26.300,0:34:34.860
HarfBuzz also has fancy features like[br]variable widths or weight

0:34:34.860,0:34:45.760
with only one font or you can define[br]in the font characters with

0:34:45.760,0:34:55.540
variable widths and without stepping you[br]can change it using HarfBuzz.

0:34:59.940,0:35:04.760
Those techniques are used in[br]client-side rendering.

0:35:06.860,0:35:15.100
One library often was[br]until recently often used, Xft.

0:35:17.820,0:35:22.480
Well this is the applications meaning the[br]X clients render the text

0:35:24.060,0:35:27.280
based on FreeType and fontconfig.

0:35:27.800,0:35:31.240
Then the X server[br]only displays the results.

0:35:32.160,0:35:36.140
Well, there is some caching involved,

0:35:36.140,0:35:42.200
and it requires[br]an extension to the protocol.

0:35:51.160,0:35:56.120
In the widget libraries this was also[br]used a long time,

0:35:56.120,0:36:01.540
but now Qt, for example, has it's own[br]code for font rendering

0:36:01.540,0:36:05.240
based on HarfBuzz, FreeType,[br]and fontconfig.

0:36:05.240,0:36:09.140
There's the combination of[br]Pango and Cairo,

0:36:09.140,0:36:13.000
which is used in the GTK environment.

0:36:13.000,0:36:22.660
Pango derives from Greek and Japanese:[br]pan means all and go means languages.

0:36:22.660,0:36:29.660
So this is the background to write[br]in all languages.

0:36:29.660,0:36:34.000
This also uses HarfBuzz, FreeType,[br]and fontconfig.

0:36:34.000,0:36:39.780
And if you look at Wayland clients,[br]they only do client-side rendering.

0:36:42.660,0:36:48.140
To sum it up, we have a variety of[br]techniques for text display.

0:36:50.340,0:36:53.600
Some have historical than[br]practical value nowadays.

0:36:53.600,0:36:58.940
The modern font rendering stack[br]is quite complex.

0:37:03.840,0:37:08.820
But writing is one of the[br]main interface to computers,

0:37:08.820,0:37:12.160
so developers should be aware[br]of the complexity.

0:37:14.460,0:37:16.560
Keep that in mind.

0:37:17.720,0:37:18.540
Thank you.

0:37:20.280,0:37:24.080
[applause]

0:37:33.640,0:37:35.440
Are there any questions?

0:37:41.100,0:37:45.040
[audience] More a request than a question,[br]I find the topic very interesting

0:37:45.040,0:37:51.240
and I'd like to check it again. I know[br]your video was not recorded

0:37:51.240,0:37:53.640
or I think it was not recorded...

0:37:53.640,0:37:57.080
[Max] Well it was I think.

0:37:58.340,0:38:05.320
[audience] Okay so nevermind, but still[br]if you are able to share your presentation

0:38:05.320,0:38:06.160
[Max] Yes

0:38:06.160,0:38:09.440
[audience] I would be[br]very happy to look at it.

0:38:16.960,0:38:25.640
[audience] [tests mic] What's the problem[br]due to the

0:38:25.640,0:38:32.900
compressed ?? from the software stack[br]in your open ??.

0:38:32.900,0:38:36.240
[Max] The problem of what?

0:38:36.240,0:38:48.320
[audience] What's the problem it came from[br]this complex software stack

0:38:48.320,0:38:50.320
in your open ??.

0:38:50.320,0:38:59.420
There's no problem with that,[br]or there's some problem

0:38:59.420,0:39:11.300
with these lot of layers, very lot of[br]components to render the font.

0:39:11.300,0:39:17.440
[Max] Okay, I try to rephrase the question[br][question] Please

0:39:17.440,0:39:22.820
[Max] What is the reason there is so many[br]layers in the font rendering stack today.

0:39:22.820,0:39:23.980
[Max] Is that correct?

0:39:23.980,0:39:38.120
[audience] And it caused some problem. Do[br]you know any problem

0:39:38.120,0:39:41.600
with current rendering system.

0:39:41.600,0:39:43.700
[Max] Colored font rendering system?

0:39:43.700,0:39:45.700
[audience] Current, now.

0:39:48.040,0:39:49.440
[Max] Ah current font-

0:39:49.440,0:39:52.500
[audience 2] The question is[br]whether the complexity

0:39:52.500,0:39:55.520
means that there are[br]difficulties for developers.

0:39:55.520,0:39:56.700
Is it too complex?

0:39:56.700,0:39:58.200
Does that cause problems?

0:39:58.200,0:40:02.640
[Max] Well the complexity is hidden behind[br]the font rendering stack.

0:40:02.640,0:40:10.560
So it's a huge collection of software,

0:40:10.560,0:40:17.620
usually there's HarfBuzz, fontconfig,[br]and FreeType heavily used nowadays.

0:40:17.620,0:40:22.300
But it's all encapsulated[br]in these libraries

0:40:22.300,0:40:29.140
and it's used all over[br]the free software world

0:40:30.240,0:40:39.080
and it makes it easy to write applications[br]which are easily translatable.

0:40:39.840,0:40:47.800
[audience] Yes but for example,[br]the fontconfig is not so flexible.

0:40:47.800,0:40:55.080
For example, when we're using[br]mainly[?] Japanese

0:40:55.080,0:41:01.800
and other display of the language,

0:41:01.800,0:41:13.160
then the font of config chooses the[br]non-Japanese font like the Chinese one.

0:41:13.160,0:41:28.220
I know some distributions like Ubuntu make[br]language specific fontconfig file

0:41:28.220,0:41:36.500
for each language to deal with but[br]Debian doesn't have such a mechanism.

0:41:38.880,0:41:47.800
So in my opinion the fontconfig[br]is a bit terrible so

0:41:47.800,0:41:55.260
is there any ?? meant or any hack for it?

0:41:55.260,0:42:04.760
[Max] Okay, the fontconfig system comes[br]from the time where XML was popular.

0:42:04.760,0:42:06.600
[audience] Mhmm[br][Max] As you can see.

0:42:08.520,0:42:15.360
Well the problem here is[br]not so much the software stack

0:42:15.360,0:42:18.960
more than the Unicode system.

0:42:18.960,0:42:25.300
So in the Unicode system there are[br]same code points for

0:42:25.300,0:42:31.240
Japanese and Chinese characters somewhere[br]although they have different appearances.

0:42:31.240,0:42:39.200
In the fontconfig system there are[br]replacement rules for characters

0:42:39.200,0:42:48.380
and it is just a list and usually Chinese[br]fonts are listed first.

0:42:48.380,0:42:54.540
So that is the reason why in the Japanese[br]language you get Chinese characters

0:42:54.540,0:42:56.620
instead of Japanese characters.

0:42:56.620,0:43:01.760
So I also think there's room to improve[br]the software stack, yes.

0:43:01.760,0:43:03.180
[audience] Thank you.

0:43:15.500,0:43:19.520
[Max] Okay, done. Thank you.

0:43:20.080,0:43:24.640
[applause]