Re: Rendering with xft and hinting

[Keith Packard <keithp keithp com>]

Around 20 o'clock on Mar 16, Owen Taylor wrote:

> There are rumours that use of the GASP table is patented by Microsoft...

US Patent 5,684,510 seems to cover the selection of rendering technique 
based on pixel size; the GASP table provides more flexibility than the 
patent requries, but I don't think that's particularily relevant to the 
patent itself.

I believe the patent doesn't affect using the GASP table itself, but only 
in combination with the particular rendering technique described by the 
patent.  It describes an anti-aliasing technique involving supersampling 
which FreeType2 doesn't use.  FreeType2 uses an analytic approach to 
sub-pixel coverage, a significant difference from supersampling.

Every claim which describes the "grayscale" rendering of fonts defines 
that in terms of supersampling and counting the subpixels hit to determine 
gray level.

The patent claims include not only selection of rendering method, but also 
the very combination of grid fitting combined with super-sampled 
anti-aliasing.  I believe FreeType1's use of super sampling along with 
hinting may fall under the scope of this patent; FreeType2 clearly does 
not.

Keith Packard        XFree86 Core Team        Compaq Cambridge Research Lab