Around 8 o'clock on Jun 3, Dr Andrew C Aitchison wrote:

> That might be nice, but Xlib.h has DisplayWidth() and DisplayWidthMM(),
> (ditto for height) and these can be set in the config file or probed via
> DDC. From these you can get the pixel pitches and aspect ratio (although
> this does assume similar screens for Xinerama). I can see that a completely
> free ratio makes snapping difficult, but it would be nice to have the
> choice of saying let the server calculate the pixel aspect ratio.

Xft is about to start ignoring the screen size entirely; the values 
present there are generally not what people really want (ref: last year's 
discussion with some torvalds goon on this topic).  And, most people 
generally want the system to assume the pixels are square; it makes things 
"look better" when they have symmetrical pixels, rather than symmetrical 
size.  It takes a rather significantly non-square pixel size ratio to make 
this relevant.

> Can you have a "probe the pixel aspect ratio value from server 
> information" option ?

I'll consider how this might look in the config file.  I might make 
it look for an X resource; that could be trivially set at login time by 
the user.

> Sorry, are you saying that that an aspect ratio of 1.2 is rounded to 1.0, 
> or that it is partially pixel aligned ie snaps on a 5:4 ?
> IIRC TVs use a pixel aspect of 1.2, so it isn't an idle speculation,
> I take it that with this change square characters remain square.

The outlines are scaled separately in X and Y dimensions, then if hinting 
is enabled, the coordinates are shifted around to fit them to the pixel 
grid as appropriate.

The result is that equal distances in the outline will remain 
approximately equal in the result, except that some distances will be 
adjusted to improve the appearance of the glyphs.  Square characters will 
remain approximately square.

Snapping the aspect ratio to whole integers would have been pretty boring 
:-)

Keith Packard        XFree86 Core Team        HP Cambridge Research Lab


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