Subpixel rendering and patents

angryfirelord · 11-27-2014, 02:08 PM

One of the things I do when I install a new Slackware system is I enable subpixel rendering so that the fonts don't look quite so horrible (specifically on Firefox). I went to the FreeType website and they stated that the bytecode patents had expired in 2010.

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

However, does the ClearType patent still apply towards subpixel rendering or is it only for the RGB layout? The diff in question looks like this:

Code:

--- ./include/freetype/config/ftoption.h.orig   2007-01-05 10:18:45.000000000 -0600
+++ ./include/freetype/config/ftoption.h        2007-04-21 15:07:04.000000000 -0500
@@ -92,7 +92,7 @@
   /* This is done to allow FreeType clients to run unmodified, forcing     */
   /* them to display normal gray-level anti-aliased glyphs.                */
   /*                                                                       */
-/* #define FT_CONFIG_OPTION_SUBPIXEL_RENDERING */
+#define FT_CONFIG_OPTION_SUBPIXEL_RENDERING

It's confusing to me because that function doesn't appear to be directly specified as patent infringing. I know Fedora doesn't enable it out of the box either, but I can't find anything tying it to ClearType (which doesn't expire until 2019).

turtleli · 11-27-2014, 02:23 PM

From the Freetype source code:

Code:

  /*************************************************************************/
  /*                                                                       */
  /* Uncomment the line below if you want to activate sub-pixel rendering  */
  /* (a.k.a. LCD rendering, or ClearType) in this build of the library.    */
  /*                                                                       */
  /* Note that this feature is covered by several Microsoft patents        */
  /* and should not be activated in any default build of the library.      */
  /*                                                                       */
  /* This macro has no impact on the FreeType API, only on its             */
  /* _implementation_.  For example, using FT_RENDER_MODE_LCD when calling */
  /* FT_Render_Glyph still generates a bitmap that is 3 times wider than   */
  /* the original size in case this macro isn't defined; however, each     */
  /* triplet of subpixels has R=G=B.                                       */
  /*                                                                       */
  /* This is done to allow FreeType clients to run unmodified, forcing     */
  /* them to display normal gray-level anti-aliased glyphs.                */
  /*                                                                       */
/* #define FT_CONFIG_OPTION_SUBPIXEL_RENDERING */