Re: Rendering with xft and hinting

[Keith Packard <keithp keithp com>]

Around 2 o'clock on Mar 17, Soeren Sandmann wrote:

> The table I am talking about is the GASP table:
> 
>     http://developer.apple.com/fonts/TTRefMan/RM06/Chap6gasp.html

Thanks for the pointer.  Reading through the Microsoft explanation
at 

	http://www.microsoft.com/typography/tt/win95tt.htm

left me wonder how relevant or accurate this information is across a wide
range of screen devices.  The table was added when typical screens were 
800x600 pixels; I suspect there are few X users with such small screens 
anymore.  As the angular size of pixels is now typically half of what is 
was then, I suspect the table has become somewhat anachronistic.

The notion that anti-aliasing should be turned off at any size is 
certainly debatable today; anyone running at 1280x1024 or higher LCD 
resolutions or 1600x1200 CRT should give pure AA text a try.

However, the point at which hinting should be applied is probably still
relevant; it gives some idea of when the fonts minimal features should be
drawn one pixel wide rather than at some fraction of a pixel.  Current, I
think FreeType "guesses" at this value; the guess seems pretty good to me,
but maybe the GASP table could provide a better guess.

> I don't know how freetype works at all, but if it provides access to
> the GASP table, then I think Xft2 should as well.

It doesn't currently provide access to this table, but it could be added 
easily -- the API for the TrueType tables is quite extensible.

What I would suggest is that the GASP table be provdied in the font 
pattern in some form; then users could select whether to follow the GASP 
rules in their configuration files, and make that choice per family.

Keith Packard        XFree86 Core Team        Compaq Cambridge Research Lab