First of all, ClearType has *two* components. The first one, subpixel hinting, is available in FreeType (via the macro TT_CONFIG_OPTION_SUBPIXEL_HINTING), is *not* patented, but it is still off by default since it needs more testing, streamlining, etc. Originally, it was part of the Infinality patch. The second one is ClearType colour filtering, also implemented in FreeType (via the macro FT_CONFIG_OPTION_SUBPIXEL_RENDERING); it *is* patented and thus off by default. Be aware that MS uses a different (and admittedly better) approach to subpixel rendering: To avoid overflows in the computations due to the increased horizontal resolution, they do super-sampling instead (this is, using normal resolution but getting information not for values 0, 1, 2, 3, ... but for 0, 0.1, 0.2, 0.3, ... or something similar instead).
'Technical' point of view. What is colour filter
http://research.microsoft.com/en-us/projects/cleartype/ https://www.grc.com/cleartype.htm http://www.beatstamm.com/typography/RTRCh2.htm#Sec2
and how it can be chosen? By FT_LCD_FILTER_*?
Yes, if compiled into FreeType.
Which is actually harmless one?
Harmless (but rather unusable) is FT_LCD_FILTER_LEGACY. Note that it is *easy* to circumvent the patent: Simply use a different but still good colour filter. The graphics system could increase the horizontal rendering resolution by, say, a factor of three, then apply a filter to reduce the resolution into proper RGB channels.
Why FT_CONFIG_OPTION_SUBPIXEL_RENDERING is off by default?
Because FT_LCD_FILTER_DEFAULT is patented, AFAIK, and FT_LCD_FILTER_LIGHT probably too. Werner -- To unsubscribe, e-mail: opensuse-factory+unsubscribe@opensuse.org To contact the owner, e-mail: opensuse-factory+owner@opensuse.org