[PATCH] Re: About the :distant-foreground face attribute

[Daniel Colascione]

On 01/08/2014 09:43 AM, Eli Zaretskii wrote:
> > From: Chong Yidong <address@hidden>
> > Cc: address@hidden,  address@hidden
> > Date: Wed, 08 Jan 2014 13:24:17 +0800
> >
> > Eli Zaretskii <address@hidden> writes:
> >
> > > > The feature does not fit well with the design of the rest of the
> > > > face-handling code.  We already have a mechanism for checking to see
> > > > when to use a particular face: the DISPLAY element in a face spec.  The
> > > > :distant-foreground face attribute, by its very existence, is redundant
> > > > with what the DISPLAY element was meant to do.  This adds extra
> > > > complexity to the design, for no good reason.

The attached patch might be another solution to the problem. It replaces 
:distant-foreground with :contrast-function, which punts the actual 
contrast logic to lisp by calling the named function during face 
realization. (Performance isn't a problem in practice because we cache 
face realizations.) In lisp, we implement four low-contrast-mitigation 
policies: do not adjust for contrast, adjust automatically (by adjusting 
CIE L*A*B color space L values), adjust automatically (by adjusting the 
V values in HSV color space), or just set the foreground to a specific 
color if the contrast dips below a certain point (the current 
:distant-foreground behavior). Both the policy and the parameters (well, 
the override color) are customizable on a per-face basis; when merging 
faces, the one with the highest priority sets the whole behavior.

The patch uses the CIE L*A*B colorspace algorithm by default. It 
produces surprisingly good results, at least in my tests, adapting 
automatically to light and dark backgrounds while preserving the hues of 
theme foreground colors.

(Changing themes nukes the face property right now, so you'll have to 
reset it each time.)

adaptive-face.patch
Description: Text Data