[OpenJDK 2D-Dev] Setting the FreeType LCD filter
Philip Race
philip.race at oracle.com
Tue Oct 16 14:15:05 UTC 2018
Yes, a reliable jtreg test seems overly hard for this case. So I'll mark
it noreg-hard.
-phil.
On 10/16/18, 12:00 AM, Laurent Bourgès wrote:
> Phil,
> I tested John's patch sucessfully, it is complicated to write a jtreg
> Test...
>
> OK for me as it is.
>
> Laurent
>
> Le mar. 16 oct. 2018 à 08:40, Philip Race <philip.race at oracle.com
> <mailto:philip.race at oracle.com>> a écrit :
>
> I intend to push this with myself & Laurent as reviewers.
>
> OK by all ?
>
> -phil.
>
> On 10/11/18, 12:22 PM, Phil Race wrote:
> > Very well done analysis of the options and very thorough testing of
> > the effects
> > on the different libraries/platforms.
> >
> >
> > > There are some alternatives to setting the filter:
> > > • Bundle the FreeType library by default
> >
> > Although the build makes this easy to set as an option, we
> decided we
> > prefer to
> > use the platform library on Linux - and Solaris for that matter
> - in
> > our releases.
> >
> > So setting this option is going to be needed for some years to
> come,
> > until
> > even a Linux current release like Ubuntu 18.04 is obsolete.
> >
> > We can't re-use the OpenJavaFX bug ID, and surprisingly I can't
> find
> > an open
> > bug on this for 2D. So I've submitted
> > https://bugs.openjdk.java.net/browse/JDK-8212071
> >
> > And I've attached John's images to the bug report and pasted his
> email
> > in there.
> >
> >
> >
> > -phil.
> >
> >
> > On 10/11/2018 10:56 AM, John Neffenger wrote:
> >> On 10/10/2018 11:15 AM, Laurent Bourgès wrote:
> >>> It looks awesome & promising.
> >>
> >> Thank you, Laurent, for looking into it so quickly!
> >>
> >>> PS: It is better to send plain text (long) email than sending
> >>> external links (github).
> >>
> >> Thanks for the tip. Right, Web pages and repositories can be
> deleted,
> >> so here it is, for the record ...
> >>
> >> The symptoms of the problem are the same as in the link below, but
> >> they appear in AWT and Swing applications instead of JavaFX
> >> applications.
> >>
> >> JDK-8188810: Fonts are blurry on Ubuntu 16.04 and Debian 9
> >> https://bugs.openjdk.java.net/browse/JDK-8188810
> >>
> >> The description of the problem on the Java side follows.
> >>
> >> Synopsis: Reduce color fringes in FreeType subpixel rendering
> >>
> >> The text in Java applications often has severe color fringes when
> >> using OpenJDK on Ubuntu and other Debian-based distributions
> because
> >> the JDK fails to set the LCD filter. Adding two lines of code
> to the
> >> file freetypeScaler.c fixed the problem in my tests, without any
> >> regression errors for other Linux distributions. The patch is
> >> attached to this message as the file freetypeScaler.diff.
> >>
> >> There are some alternatives to setting the filter:
> >>
> >> • Bundle the FreeType library by default and always use the new
> >> Harmony subpixel rendering technique. This option removes the
> >> uncertainty in the library at the expense of an additional 4.6
> >> megabytes to the installed size — an increase of less than one
> >> percent. OpenJDK 12 even includes the latest FreeType 2.9.1, a
> newer
> >> version than the one found on most systems.
> >>
> >> • Wait another year and see what changes are made to
> FreeType, if
> >> any, when the ClearType patents expire. This option, though,
> doesn’t
> >> solve the problem that users of Ubuntu and other Debian-based
> >> distributions have now.
> >>
> >> The problem originates in decisions made by the developers of
> >> FreeType, Debian, Fedora, and OpenJDK concerning the Microsoft
> >> ClearType patents [1].
> >>
> >> • In 2007, FreeType 2.3.0 added a compiler configuration
> macro to
> >> the file ftoption.h named FT_CONFIG_OPTION_SUBPIXEL_RENDERING. If
> >> defined, the FreeType library includes patented ClearType
> techniques
> >> in its subpixel rendering.
> >>
> >> But there’s a catch. When the ClearType methods are
> enabled, the
> >> subpixel rendering is not filtered, which results in severe color
> >> fringes. Clients of the FreeType library must make an explicit
> call
> >> to the function FT_Library_SetLcdFilter to apply color
> filtering. The
> >> filter was disabled by default, explained one of its authors, “to
> >> avoid major surprises to existing clients, including libXft and
> Cairo
> >> which already perform some wacky color filtering on top of
> FreeType.”
> >>
> >> • In 2009, Debian created a patch to FreeType 2.3.9, named
> >> enable-subpixel-rendering.patch, that defines the macro and
> enables
> >> ClearType-style rendering. The change log states, “This is
> considered
> >> no more or less evil than the bytecode interpreter which we also
> >> enable.” Ubuntu, based on Debian, applies the patch as well.
> Fedora
> >> created the same patch in 2007, named
> >> freetype-2.3.0-enable-spr.patch, but does not apply the patch by
> >> default.
> >>
> >> • In 2017, FreeType 2.8.1 included a new subpixel rendering
> >> technique, called Harmony, that is nearly identical in output
> to the
> >> ClearType technique but uses a different algorithm, avoiding the
> >> patents. FreeType now uses Harmony subpixel rendering when the
> >> ClearType methods are disabled, with no need for clients to set
> the
> >> LCD filter. (This would have been a good time for Debian to remove
> >> its subpixel rendering patch.) The latest Fedora Workstation 28
> runs
> >> FreeType 2.8.0, which does not include Harmony.
> >>
> >> • In 2019, the Microsoft ClearType patents expire.
> >>
> >> So now we have two variants of the FreeType library: one that
> >> requires a function call to set the LCD filter in Ubuntu and other
> >> distributions based on Debian, and another that doesn’t require
> the
> >> function call in Red Hat Enterprise Linux, Oracle Linux, and other
> >> distributions based on Fedora.
> >>
> >> To demonstrate the problem, I built four versions of the JDK
> from the
> >> latest OpenJDK sources. I built a version that uses the system
> >> FreeType library and another that uses the bundled FreeType
> library.
> >> Then I changed the OpenJDK code to set the default LCD filter and
> >> built the two versions again. The four builds were named:
> >>
> >> jdk-12-system-lcdnone
> >> jdk-12-system-lcddefault
> >> jdk-12-bundled-lcdnone
> >> jdk-12-bundled-lcddefault
> >>
> >> The system library is FreeType 2.8.1 in Ubuntu 18.04.1 LTS,
> which has
> >> the Debian patch applied (ClearType methods enabled), while the
> >> bundled library is FreeType 2.9.1 in OpenJDK 12, which uses the
> >> library default (ClearType methods disabled). I wrote a simple
> Java
> >> Swing application called FontDemo [2] that displays two text areas
> >> with the Adobe Source Code Pro font [3] in TTF and OTF formats
> (the
> >> latest non-variable download).
> >>
> >> The results are shown in the two images attached to this message:
> >>
> >> fontdemo.png
> >> Three screenshots of the FontDemo program
> >>
> >> fontdemo-detail.png
> >> Details from the screenshots scaled by 800 percent
> >>
> >> When using the Ubuntu system FreeType library, setting the LCD
> filter
> >> is critical. The screenshots show the ClearType-style rendering
> >> without setting the LCD filter, and after adding the change to set
> >> the filter. The ClearType configuration macro is defined in the
> >> Ubuntu build of FreeType, so the function to set the filter
> returns
> >> success (0) when called and applies color filtering.
> >>
> >> When using the OpenJDK bundled FreeType library, setting the LCD
> >> filter does nothing. The screenshots show the FreeType Harmony
> >> rendering, which is the same whether or not the LCD filter is set.
> >> The ClearType configuration macro is not defined in the OpenJDK
> build
> >> of FreeType, so the function to set the filter returns
> >> FT_Err_Unimplemented_Feature (7) when called and does nothing.
> >>
> >> The test system I used is a QEMU/KVM guest virtual machine running
> >> Ubuntu 18.04.1 LTS (Bionic Beaver) with the details shown
> below. The
> >> display is a 27-inch Dell UltraSharp U2717D monitor with a
> resolution
> >> of 2560 × 1440 pixels at 109 pixels per inch.
> >>
> >> ubuntu at bionic:~$ uname -a
> >> Linux bionic 4.15.0-36-generic #39-Ubuntu SMP
> >> Mon Sep 24 16:19:09 UTC 2018 x86_64 x86_64 x86_64 GNU/Linux
> >>
> >> ubuntu at bionic:~$ ldd --version
> >> ldd (Ubuntu GLIBC 2.27-3ubuntu1) 2.27
> >>
> >> ubuntu at bionic:~$ getconf GNU_LIBPTHREAD_VERSION
> >> NPTL 2.27
> >>
> >> ubuntu at bionic:~$ $HOME/opt/jdk-12-system-lcdnone/bin/java -version
> >> openjdk version "12-internal" 2019-03-19
> >> OpenJDK Runtime Environment (build 12-internal+0-adhoc.ubuntu.jdk)
> >> OpenJDK 64-Bit Server VM (build 12-internal+0-adhoc.ubuntu.jdk,
> mixed
> >> mode)
> >>
> >> Below are the full test results using five versions of FreeType
> built
> >> first with the ClearType methods disabled (the default) and then
> >> again with them enabled. I ran all 10 libraries under OpenJDK 12,
> >> first with no LCD filter and then again after adding the code
> to set
> >> the default LCD filter.
> >>
> >> No LCD Filter
> >>
> >> 2008 FreeType 2.3.5 (libfreetype.so.6.3.16) in Ubuntu 8.04 LTS
> >> ClearType Off: Grayscale, ClearType On: Mild fringes
> >>
> >> 2014 FreeType 2.5.2 (libfreetype.so.6.11.1) in Ubuntu 14.04 LTS
> >> ClearType Off: Grayscale, ClearType On: Severe fringes
> >>
> >> 2016 FreeType 2.6.1 (libfreetype.so.6.12.1) in Ubuntu 16.04 LTS
> >> ClearType Off: Grayscale, ClearType On: Severe fringes
> >>
> >> 2018 FreeType 2.8.1 (libfreetype.so.6.15.0) in Ubuntu 18.04 LTS
> >> ClearType Off: Harmony, ClearType On: Severe fringes
> >>
> >> 2019 FreeType 2.9.1 (libfreetype.so.6.16.1) in OpenJDK 12
> >> ClearType Off: Harmony, ClearType On: Severe fringes
> >>
> >> The OpenJDK does not set the FreeType LCD filter, so there are
> severe
> >> color fringes when using a FreeType library built with the
> ClearType
> >> methods enabled. The only reason the older FreeType 2.3.5 shows
> mild
> >> color fringes is because it uses full hinting, so the glyphs are
> >> simply too skinny to see their colors.
> >>
> >> Default LCD Filter
> >>
> >> 2008 FreeType 2.3.5 (libfreetype.so.6.3.16) in Ubuntu 8.04 LTS
> >> ClearType Off: Grayscale, ClearType On: ClearType filtered
> >>
> >> 2014 FreeType 2.5.2 (libfreetype.so.6.11.1) in Ubuntu 14.04 LTS
> >> ClearType Off: Grayscale, ClearType On: ClearType filtered
> >>
> >> 2016 FreeType 2.6.1 (libfreetype.so.6.12.1) in Ubuntu 16.04 LTS
> >> ClearType Off: Grayscale, ClearType On: ClearType filtered
> >>
> >> 2018 FreeType 2.8.1 (libfreetype.so.6.15.0) in Ubuntu 18.04 LTS
> >> ClearType Off: Harmony, ClearType On: ClearType filtered
> >>
> >> 2019 FreeType 2.9.1 (libfreetype.so.6.16.1) in OpenJDK 12
> >> ClearType Off: Harmony, ClearType On: ClearType filtered
> >>
> >> After changing the OpenJDK to set the default LCD filter, there
> is no
> >> version of the FreeType library that shows the severe color
> fringes.
> >> Note that Fedora Workstation 28 includes FreeType 2.8.0 with the
> >> ClearType methods disabled, so it displays grayscale anti-aliasing
> >> for the OpenJDK whether it sets the LCD filter or not. (FreeType
> >> 2.8.0 does not include Harmony.)
> >>
> >> For background information on LCD filters see Section 2.2.1 [4] of
> >> The Raster Tragedy at Low-Resolution, which has an interactive
> >> demonstration of the filters used in ClearType (Microsoft),
> CoolType
> >> (Adobe), FreeType (open source), and Quartz 2D (Apple). Hover your
> >> mouse over each of the samples in the illustration to remove
> the filter.
> >>
> >> Below is the relevant section of the file ftoption.h in FreeType
> >> 2.9.1 bundled with OpenJDK 12, edited for formatting:
> >>
> >>
> java.desktop/share/native/libfreetype/include/freetype/config/ftoption.h
> >>
> >> /*
> >> Uncomment the line below if you want to activate LCD rendering
> >> technology similar to ClearType in this build of the library. This
> >> technology triples the resolution in the direction color subpixels.
> >> To mitigate color fringes inherent to this technology, you also
> need
> >> to explicitly set up LCD filtering.
> >>
> >> Note that this feature is covered by several Microsoft patents
> >> and should not be activated in any default build of the library.
> >> When this macro is not defined, FreeType offers alternative LCD
> >> rendering technology that produces excellent output without LCD
> >> filtering.
> >> */
> >> /* #define FT_CONFIG_OPTION_SUBPIXEL_RENDERING */
> >>
> >> [1] http://david.freetype.org/cleartype-patents.html
> >> [2]
> >>
> https://github.com/jgneff/openjdk-freetype/blob/master/src/org/status6/FontDemo.java
> >> [3] https://github.com/adobe-fonts/source-code-pro
> >> [4] http://rastertragedy.com/RTRCh2.htm#Sec21
> >
>
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