[OpenJDK 2D-Dev] Setting the FreeType LCD filter

Thu Oct 11 18:41:07 UTC 2018

John,

Sorry but attachments are rejected if larger than 100 kb, then your email
is being moderated.

You should put resources online, preferably on openjdk.java.net.

Maybe just send text and your diff only and keep images as link on github.

Laurent

Le jeu. 11 oct. 2018 à 19:56, John Neffenger <john at status6.com> a écrit :

> 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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