Running Qt/KDE Atop An OpenGL Stack

[phoronix]

Phoronix: Running Qt/KDE Atop An OpenGL Stack

Zack Rusin, the well-known X.Org and KDE hacker, has written a new blog post concerning the Qt tool-kit and the different options that are available when it comes to rendering graphics. Qt currently can target a pure CPU raster engine, using X11 with the X Render extension for providing some GPU-assisted acceleration, or using an OpenGL engine...

http://www.phoronix.com/vr.php?view=NzQ1NA

[wswartzendruber]

Yeah now that DRI2 is finally here.

[spykes]

the quicker we get the rendering stack to work on top of OpenGL the better off we'll be
Isn't what's actually doing the Clutter toolkit ?
Anyway, it's good to see that everybody is going in this direction.
Graphic cards are all designed for 3D rendering those days, so it makes sense to use 3D API even to draw 2D UI.

[thefirstm]

Something that nobody ever mentioned: using the OpenGL stack, it evidently turns of subpixel text rendering.

[BlackStar]

Something that nobody ever mentioned: using the OpenGL stack, it evidently turns of subpixel text rendering.

There's no technical reason to turn off subpixel AA for text when using OpenGL. I have coded a cross-platform OpenGL text engine that looks 100% identical to the underlying font renderer (kerning, subpixel AA).

That said, there are many ways to render text using OpenGL, each with different tradeoffs between speed, memory consumption and quality. My guess is that a) this is a plain old bug (note: Qt4 had completely broken subpixel AA until version 4.5) or b) Qt opts to reduce quality in favor of memory consumption (which is flat-out wrong, IMO).

[thefirstm]

I didn't think it was impossible to do subpixel with OpenGL, I was just saying that it didn't, and that keeps me from using the OGL mode.

[BlackStar]

I didn't think it was impossible to do subpixel with OpenGL, I was just saying that it didn't, and that keeps me from using the OGL mode.

Absolutely agreed - the same thing that's stopping you from using Qt/OGL now, stopped me from using any Qt4 application prior to Qt4.5.

Text rendering is the single most important aspect of any user interface. I wish Qt developers would understand that.

[nanonyme]

Absolutely agreed - the same thing that's stopping you from using Qt/OGL now, stopped me from using any Qt4 application prior to Qt4.5.

Text rendering is the single most important aspect of any user interface. I wish Qt developers would understand that.Yeah, assuming you're dealing with humans instead of apes who can't read anyway. :3

[energyman]

I didn't think it was impossible to do subpixel with OpenGL, I was just saying that it didn't, and that keeps me from using the OGL mode.

really? I started kwin with opengl and konqueror - and the fonts looked like the rest.
Ah, wait, I don't use subpixel hinting, because I don't like it.

[RealNC]

really? I started kwin with opengl and konqueror - and the fonts looked like the rest.
Ah, wait, I don't use subpixel hinting, because I don't like it.

Then what's your point? He said OpenGL currently breaks subpixel rendering. You don't use subpixel rendering. What's the point of your post?

[energyman]

My point is, some peole act like subpixel hinting is most important and not having it makes opengl worthless. Read postings 7 and 8.
While in fact a lot of people don't even have it on, because it degrades readability (for them).

[RealNC]

OpenGL would be worthless to me if I can't have subpixel hinting. Obviously there's a group of people like me who can't accept a system without it. Period. If I had to choose right now between the two, I'd choose subpixel rendering any time.

[energyman]

so what? just because you and some other see it as must have feature does not make it true for everybody. So acting like you/they are talking for everybody is incorrect.

[RealNC]

so what?

So what "what?" It's an important feature to many people.

What kind of answer do you expect when asking "so what?" I'm not gonna bomb the Trolltech office. Or blackmail Nokia. If that's what you're asking.

[energyman]

yes, it is important to some people. And not important at all to others. So acting like it is the most important feature rendering qt useless without is... a bit wrong. Don't you think.

[RealNC]

Why wrong? It's my thinking exactly.

Note: *my* thinking. Obviously you have a problem separating other people's personal opinions from your own.

[energyman]

no, I am fine. I acknowledge that different people have different needs. It is you guys acting like your view is the only valid one. Reality check is needed.

[BlackStar]

no, I am fine. I acknowledge that different people have different needs. It is you guys acting like your view is the only valid one. Reality check is needed.

Where did you get that from? Noone said you have to use subpixel AA if you don't like it.

However, this doesn't change the fact that subpixel AA is one of the most important features of any modern font engine meant for monitors. Windows, Mac OS X and most Linux distros ship with subpixel AA enabled, precisely because it improves text quality on the vast majority of monitors.

So no, don't use subpixel AA if you don't like it. This doesn't excuse Qt being released with broken text rendering (and I'm not referring to the current situation with the OpenGL renderer).

[yotambien]

Where did you get that from? Noone said you have to use subpixel AA if you don't like it.

However, this doesn't change the fact that subpixel AA is one of the most important features of any modern font engine meant for monitors. Windows, Mac OS X and most Linux distros ship with subpixel AA enabled, precisely because it improves text quality on the vast majority of monitors.

So no, don't use subpixel AA if you don't like it. This doesn't excuse Qt being released with broken text rendering (and I'm not referring to the current situation with the OpenGL renderer).

But that's not how things are at the moment, and they only seem bound to get worse. Nowadays, if you don't want to use "subpixel rendering" you have to hack the hell out of obscure configuration files. Try to disable it in Windows Vista, and you'll see that if you really want to take rid of it you have to log in as administrator and change some registry keys (and even then the monster doesn't completely go away). In linux, I remember having to look up the beautiful syntax of fontconfig and change it accordingly. Yet, some applications have their own (stupid) ideas about how to display the fonts and you have to take care of them on an individual basis. To make things worse, once you've dug enough to set everything as you like, you discover that after an update some application decides to ignore the previous settings and we're back to square one. Mac OS I don't know about.

So yes, "subpixel rendering" is important, but only because a lot of people (the majority, perhaps?) care about it. It does not, however, improve the quality of anything. And life is surely easier if you like it than if you don't.

[energyman]

I just turn it off in kde's system-settings ;)

[yotambien]

I don't use KDE or any other desktop manager. Still, back when I did, I remember having to configure separately Openoffice. Also I remember vaguely doing something with Firefox and xpdf. Actually it was xpdf the application that one happy day suddenly chose to ignore my previous settings...

IF today _all_ applications actually honour the system wide (or what you would hope to be system wide) settings, and those can be easily set up within a GUI, we (or at least I) have something to celebrate.

[BlackStar]

Nowadays, if you don't want to use "subpixel rendering" you have to hack the hell out of obscure configuration files

Using Gnome, I can disable subpixel AA with 3 clicks (Appearance -> Fonts -> Best Shapes). Both GTK and Qt applications seem to honor this setting (this wasn't the case with Ubuntu 8.10-, but seems to be working as advertized in 9.04 - finally!) Even OpenOffice and VirtualBox revert to greyscale AA when they didn't before.

It does not, however, improve the quality of anything.

Microsoft, Apple and Gnome have done extensive usability studies on text rendering. They didn't pull subpixel AA out of their collective asses.

See, for example, here (http://blogs.msdn.com/fontblog/archive/2005/12/13/503236.aspx):

"Overall, the study participants read the ClearType sentences statistically reliably faster than the sentences rendered in black & white (called aliased here). The magnitude of effect is approximately 5%. [...]

Additionally, the participants made more correct responses when the text was presented in ClearType. [...] There was a statistically reliable accuracy improvement ClearType with a smaller effect magnitude of about 2%."

And life is surely easier if you like it than if you don't.

Any default setting will alienate some people, that's a given. Fortunately, you are using Linux - changing a setting is relatively easy (no need to be an admin, like on Windows); you can report an issue and request a different default; you can contribute to your favorite distro to the point they let you change the default; you can even roll your own distro with you own defaults, if you wish!

[yotambien]

Using Gnome, I can disable subpixel AA with 3 clicks (Appearance -> Fonts -> Best Shapes). Both GTK and Qt applications seem to honor this setting (this wasn't the case with Ubuntu 8.10-, but seems to be working as advertized in 9.04 - finally!) Even OpenOffice and VirtualBox revert to greyscale AA when they didn't before.

Yes, as I said, this is something to celebrate. Massive improvement.


Microsoft, Apple and Gnome have done extensive usability studies on text rendering. They didn't pull subpixel AA out of their collective asses.

I was aware of those. Well, to be honest, I don't know up to what point the Gnome crowd did any serious stuff on this front (do they have the resources to do it?). The link you provided is very interesting; unfortunately I don't have access to that journal, I am very curious (somebody here could PM it to me? :D ). From the abstract:

"Four experiments measured the effects of subpixel addressing (Microsoft's ClearType) relative to standard (aliased) font-rendering techniques."

So it's not clear to me what were they comparing. Deactivating subpixel rendering can be disastrous if the font is of mediocre quality. The automatically hinted fonts are usually horrible, only the manually, well hinted ones give the nicest results. I have a hard time believing that people find more legible a well hinted font at a right size (critical) than a clear type one. But sure, it may very well be true, and I really believe that the majority of people prefer clear type. I'm OK with that as long as I have the choice and that choice is simple to make.


Any default setting will alienate some people, that's a given. Fortunately, you are using Linux - changing a setting is relatively easy (no need to be an admin, like on Windows); you can report an issue and request a different default; you can contribute to your favorite distro to the point they let you change the default; you can even roll your own distro with you own defaults, if you wish!

I'm not as optimistic as you are. And you have acknowledged that in the past things weren't as straightforward as you and energyman describe for the current situation. At work I use OpenSuse (some version, I don't remember) and I can't change it to my liking; not in an easy way, at least. Even if I banged somebody in some mailing list that machine is not going to be upgraded any time soon. In practical terms, linux distributions shipped before _insert date here_ are crippled in a way that you can't easily choose the font rendering. I don't want to enter into rant mode, so let's forget about rolling my own distro, OK?

[deanjo]

So yes, "subpixel rendering" is important, but only because a lot of people (the majority, perhaps?) care about it.

Well I would venture to say a large majority don't even know about it. They simply use what is first presented to them.

[deanjo]

I'm not as optimistic as you are. And you have acknowledged that in the past things weren't as straightforward as you and energyman describe for the current situation. At work I use OpenSuse (some version, I don't remember) and I can't change it to my liking; not in an easy way, at least. Even if I banged somebody in some mailing list that machine is not going to be upgraded any time soon. In practical terms, linux distributions shipped before _insert date here_ are crippled in a way that you can't easily choose the font rendering. I don't want to enter into rant mode, so let's forget about rolling my own distro, OK?

Your correct, it is disabled by default for potential patent infringing reasons in openSUSE and a few others. It is also disabled by default by the upstream freetype2 folks for the same reasons. If you wish to enable it there is a wiki entry with a one-click install for it. http://opensuse-community.org/SubpixelHinting

[yotambien]

Your correct, it is disabled by default for potential patent infringing reasons in openSUSE and a few others. It is also disabled by default by the upstream freetype2 folks for the same reasons. If you wish to enable it there is a wiki entry with a one-click install for it. http://opensuse-community.org/SubpixelHinting

Oooh, I had completely forgotten about this issue (bad memories fade away). It's true, my first attempts at having decent fonts involved compiling a library (freetype I guess) to include the bytecode interpreter. Shortly after (Etch time more or less) Debian included it by default, and you only had to change some configuration files and tell fontconfig to use it.

This is, to some extent, surprising. I always had the feeling that the folks at Debian legal were extremely cautious about these things, and yet it's just the commercial distributions the ones avoiding the interpreter (or not just them?). Of course, it makes sense that they prefer to stay free of any possible litigation.

The patents, by the way, are held by Apple, and affect both antialiasing lovers and haters. The guys at freetype explain it here:

http://www.freetype.org/patents.html

My favourite rants about subpixel smoothing are those of Tuomo V:

http://modeemi.fi/~tuomov/b//archives/2006/03/17/T20_15_31/

http://modeemi.fi/~tuomov/b/archives/2008/03/20/T13_47_17/

In the first of them he gives the following link where you can see what are the differences among using no hinting, hinting and using the interpreter, for both antialiased and non antialiased fonts (bottom of the page):

http://mail.gnome.org/archives/gtk-devel-list/2002-March/msg00429.html

Again, if they really managed to sort all this out with a simple mouse click they are heroes.


PS. To install the OpenSuse packages you have to log in as root, which is a no-no at work.

[RealNC]

PS. To install the OpenSuse packages you have to log in as root, which is a no-no at work.

Unpacking to your home dir and using LD_PRELOAD is your friend :D

[BlackStar]

Apple's patents end this October or so (there was an announcement in the FreeType list, a few months ago).

And there was much rejoicing!

[deanjo]

Apple's patents end this October or so (there was an announcement in the FreeType list, a few months ago).

And there was much rejoicing!

Well actually you have to take a look at the last date on the given patent. With subpixel hinting this would be US5325479: Method and apparatus for moving control points in displaying digital typeface on raster output devices (http://www.delphion.com/details?pn=US05325479__)

Which was given submitted May 28, 1992. So realistically FreeType won't be in the free and clear until 2012 and I wouldn't count on any mainstream distro enabling it by default until that time.

[Ex-Cyber]

Well actually you have to take a look at the last date on the given patent. With subpixel hinting this would be US5325479: Method and apparatus for moving control points in displaying digital typeface on raster output devices (http://www.delphion.com/details?pn=US05325479__)

Which was given submitted May 28, 1992. So realistically FreeType won't be in the free and clear until 2012 and I wouldn't count on any mainstream distro enabling it by default until that time.If you look up that patent in the USPTO database, it says:

Notice: The portion of the term of this patent subsequent to October 13, 2009 has been disclaimed.

[energyman]

so - with all the patents - are you 'subpixel is a must' people even sure that you have that stuff enabled? What about a side by side comparism?

[RealNC]

so - with all the patents - are you 'subpixel is a must' people even sure that you have that stuff enabled?

I am. On Gentoo you have to enable the "cleartype" USE flag to get packages that contain the patches.

For libXft (older programs use this) I use my own ebuild in the local overlay to apply libXft-2.1.10-lcd-cleartype.diff.

We aren't clueless, energyman :D

[energyman]

well, I just turned it on - and I am disgusted so far...

[RealNC]

I'm disgusted without it.

Though the results without the bytecode interpreter in freetype are poor ("bindist" USE flag of freetype). Also, the interpreter has to explicitly be enabled. I was tweaking /etc/fonts/local.conf for hours to get the results I wanted. However, if you don't like font rendering that looks like the one in Mac OS X, you will still be disgusted I guess. Me, I can't live without it.

Edit:
Just to make sure we're seeing the same thing here:

http://i28.tinypic.com/ju766h.png

And of course if you happen to view this on a CRT monitor instead of a TFT (CRTs don't have subpixels), or on a TFT that doesn't use RGB subpixel alignment, the fonts will look like some abomination from hell.

[deanjo]

If you look up that patent in the USPTO database, it says:

Good catch, however I'm not sure that can be said on all off the patents. There is also Canadian, UK, and German patents on those items. Until all those are cleared distro's like openSUSE will stay clear of them much like they have with the mpeg codecs and such.

[Ant P.]

The best setting I've found is subpixel AA and hinting set to full (everything else left alone) - the default hinting level makes everything blurry.

I can't stand Windows' cleartype and I don't see why anyone would want to emulate it either.

[RealNC]

I agree on that. Windows' implementation of Cleartype makes fonts jump almost to bold just by increasing size by 1pt. It's heavily annoying.

(Btw, this happens with full hinting so I wonder why you're using it too even though you claim you hate the Windows behavior.)

[loonyphoenix]

On Ubuntu subpixel seems to be enabled by default. Or is it not the same subpixel?

Anyway, I like normal hinting better. It looks good regardless how far from the screen you are; and I've found that close up, subpixel rendering can be seen as colored edges on fonts, which I don't like. And it IS still troublesome to make fonts look alike in all applications, at least in Ubuntu. GTK+ applications follow the settings in Gnome's configuration (duh), and so does OpenOffice, and so does Firefox. However, QT applications give a lot of trouble. Some of them can be fixed by installing the systemsettings package (it's KDE's control panel thing); however, others (Opera for one and some QT3 applications) don't even acknowledge those settings and only submit to ~/.fonts.conf or /etc/fonts/conf.d.

[BlackStar]

The best setting I've found is subpixel AA and hinting set to full (everything else left alone) - the default hinting level makes everything blurry.

I can't stand Windows' cleartype and I don't see why anyone would want to emulate it either.

Agreed on Windows cleartype - it tends to chew on fonts a bit too much.

My personal preference is subpixel AA with slight hinting. Slight hinting is a work of genious, actually: it only hints and grid-aligns the y-direction (where monitor DPI is limited) and leaves the x-direction untouched (where monitor DPI is effectively tripled due to subpixel AA). This is the best compromise between legibility and typographic accuracy: letter forms remain truthfull to their original shape but appear crystal clear on the upper and lower parts (which is where the human brain focuses to recognize letters).

As such, slight hinting manages to strike a balance between Mac OS X font rendering (which many find a tad too blurry) and Windows (full hinting, which hurts letter shapes). Add a good font and you are in typographic heaven! :p

Ok, not exactly, but I've managed to wow Mac OS X users with my Linux desktop (what font is this, it's beatiful!) and that's saying a lot. :D

My Arch settings: bytecode interpreter; subpixel AA; slight hinting; font bitmaps forced off; Calibri 11pt as desktop font; FreeType, fontconfig, libxft from AUR with Ubuntu patches. Add a good TFT or CRT monitor (the higher DPI the better) and the result *rocks*.

I really can't see how you could prefer grayscale AA - unless you are using a 10year old CRT with convergence problems or low-DPI TFT, eg 15.4'' @1280x800.

Edit: indeed, Ubuntu Intrepid+ have the exact settings I described by default. Nice!

Edit 2: RealNC, your desktop is beatiful (you are using no hinting - similar to Mac OS X). Starting with KDE 4.2 / Qt4.5 you can actually enable slight hinting without destroying your fonts (Qt had a bug previously that treated sligh as full hinting when subpixel AA was enabled) - have you tested that? It should make text slightly more legible (by taking care of the bluriness above letterforms) without hurting its appearance.

[loonyphoenix]

@BlackStar: I prefer grayscale even though I have a 125 DPI LCD monitor which renders subpixels rather nicely :) I've tried every other alternative (including subpixel + slight hinting and subpixel + strong hinting), and strong hinting + grayscale is what looks most pleasing to my eye. Moreover, I find that some fonts render even better with monochrome (black&white + strong hinting), and those include Redhat's Liberation fonts. However, others look horrible with that setting, so, unless I figure out how to enable monochrome only for select fonts, grayscale strong hinting will have to do.

As you said, much depends on the font used, and maybe some fonts are better with subpixel rendering, but grayscale rendering works best with most fonts, so it's a safe default for me. Calibri, as far as I understand, is a proprietary font from Microsoft, so it's definitely not an option. And even if it was, you can't tell web browsers only to use those fonts that render good with subpixel; they use DejaVu and Liberation fonts most of the time.

[BlackStar]

Calibri, as far as I understand, is a proprietary font from Microsoft, so it's definitely not an option. And even if it was, you can't tell web browsers only to use those fonts that render good with subpixel; they use DejaVu and Liberation fonts most of the time.

Calibri is a proprietary font by Ascender Corporation (http://www.ascendercorp.com/), not Microsoft - still not a choice if you'd prefer free fonts, but better than Microsoft I guess. ;)

Unfortunately, there are precious few fonts under the SIL or similar open licenses. Droid is a great font (unsure about the license, but you can use it for free) that works good on the desktop. Gentium is also nice, but that's not really meant for the desktop. I never really liked Liberation or Bitstream Vera (DejaVu), though (just a matter of preference, pretty much like saying you don't like the orange color :).)

That said, you definitely *can* tell a browser to render only the fonts you like. The actual method differs from browser to browser, but I know for a fact that this is possible in Opera (via user CSS) and Firefox (there is a preference, IIRC).

[loonyphoenix]

@BlackStar: Okay, technically you might be able to tell the browser which fonts to use, but it's not easy. Moreover, sometimes sites are made with a certain font in mind, and if you substitute it, the site looks ugly (bad practice, in my opinion, but nothing we can do about it). That's what Liberation fonts are for, in my mind: substituting for Arial and Times New Roman and Curier New where you must :) And in my opinion, these, along with the DejaVu family, are still the best all-purpose fonts you can find in the free software world. I haven't tried Droid, though, and am installing it currently :)

PS: Now I've tried Droid, and I don't like how it's hinted. It's blurred whatever options I use: subpixel, grayscale or black&white rendering; full, slight or no hinting. The best is still grayscale + full, because it looks the least blurred there. But I guess that's a matter of taste, the same as you not liking DejaVu and Liberation :)

[BlackStar]

PS: Now I've tried Droid, and I don't like how it's hinted. It's blurred whatever options I use: subpixel, grayscale or black&white rendering; full, slight or no hinting. The best is still grayscale + full, because it looks the least blurred there. But I guess that's a matter of taste, the same as you not liking DejaVu and Liberation :)

Yep, fonts seem to be a matter of taste (and don't dare challenge someone on his choice of programming fonts!) :)

Droid was designed for the Android platform (think small mobile screens), so it probably looks best there. I don't recall any bluriness on Droid 10pt w/ slight hinting & subpixel, but then again "bluriness" is another subjective matter (cue Mac OS X with its blurry fonts - many people *love* them).

I just tried grayscale AA again. Impressions: on my laptop it looks significantly worse (Dell D830 @1680x1050): curves lose definition and become aliased (e.g. letters '(' and ')'), while diagonals become too thick compared to straight lines (e.g. (e.g. letter 'x' or 'κ'). On my CRT the effect is nowhere near as pronounced (Nec FE991SB @1400x1050 with Trinitron grid). Diagonals are still slightly unbalanced, but this fact is offset by the lack of color fringing.

Put together, I prefer subpixel AA on the TFT - there is no visible color fringing and text looks significantly better with it. On my CRT I could use either mode without issue, which means I'll stick with subpixel since I tend to connect both monitors in dual head.

Damn, now I'll have to go around my house and check every single monitor... :p

[RealNC]

Edit 2: RealNC, your desktop is beatiful (you are using no hinting - similar to Mac OS X). Starting with KDE 4.2 / Qt4.5 you can actually enable slight hinting without destroying your fonts (Qt had a bug previously that treated sligh as full hinting when subpixel AA was enabled) - have you tested that?

The fonts in the screenshot *do* use slight hinting actually. It's just that there's a small difference between Gtk/Qt3 apps (Firefox and KDE3 apps) and Qt4. Qt4 renders a bit sharper (I like that). Gtk and Qt 3 (with the cleartype patch applied to libXft) a tiny bit blurrier. Fortunately, I can't easily make out the difference unless I look quite close at the monitor.

Of course it also depends on the font used. The DejaVu fonts give good results, but I also have a knack for the MS fonts (Times New Roman, Tahoma and Verdana), designs I like very much though they tend to give less sharp results than DejaVu.

Edit:
Also let's not forget that this whole "subpixel/cleartype/grayscale" thing is also a matter of what we're used to. If someone used grayscale for several years (or subpixel rendering), he/she simply got used to it and everything else can be perceived as "uglier".

[Linuxhippy]

I guess that makes AMD really happy.

Their 2D acceleration code is completly slow and brolen in fglrx. They don't even provide the most basic XRender acceleration stuff, falling back to software all the time.

Maybe this way they can avoid writing descent linux specific drivers at all (the ogl code is shared anyway) :P
Anyway with their OGL implementation I would not run more then 10 ogl apps side-by side either ;)

- Clemens

[BlackStar]

I guess that makes AMD really happy.

Their 2D acceleration code is completly slow and brolen in fglrx. They don't even provide the most basic XRender acceleration stuff, falling back to software all the time.

Maybe this way they can avoid writing descent linux specific drivers at all (the ogl code is shared anyway) :P
Anyway with their OGL implementation I would not run more then 10 ogl apps side-by side either ;)

- Clemens

I've done stress testing with 100 OpenGL contexts side by side. It worked just fine last year and I guess it still does. ;)

[Apopas]

Just to make sure we're seeing the same thing here:

http://i28.tinypic.com/ju766h.png

RealNC your greek fonts seem so good as well?

[RealNC]

RealNC your greek fonts seem so good as well?

http://i29.tinypic.com/4tq3hy.png

[Apopas]

http://i29.tinypic.com/4tq3hy.png
In Firefox they seem perfect to me as well. What about kwrite or dolphin?

[RealNC]

The bottom-left window ("Το μέτρο της βλακείας") is Firefox. The top-right one ("Τα σκυλιά κυνηγάνε της γάτες") is Konqueror. Since Konqueror is a KDE app, fonts would look the same in KWrite and Dolphin too, so no need to post additional screens here. The top-left window is also a KDE app (the "Font installer" in KDE's System Settings.)

[Apopas]

The bottom-left window ("Το μέτρο της βλακείας") is Firefox. The top-right one ("Τα σκυλιά κυνηγάνε της γάτες") is Konqueror. Since Konqueror is a KDE app, fonts would look the same in KWrite and Dolphin too, so no need to post additional screens here. The top-left window is also a KDE app (the "Font installer" in KDE's System Settings.)
Stupid KDE, I got homework for the weekend now :cool: