Re: slow redisplay after changing cursor color

[Kim F. Storm]

Richard Stallman <address@hidden> writes:

>     I didn't change defface / custormize-face to reject :inherit from face
>     with the face-no-inherit property  (it would be nice, but I don't quite
>     know how to do that).
>
> The code that processes the user's input could check for a :inherit
> attribute, and look at the face to be inherited from.

I tried this, but got stuck -- someone who understands defface and
customize-face, please take a look...

Something like:

          (if (and (equal (car attr) :inherit)
                   (get (cdr attr) ; the face
                        'face-no-inherit))
              (error "You cannot inherit from %S" (cdr attr)))


>
> However, :inherit is not the only way to use a face.
>
> What happens, with your code, if someone simply gives an overlay a
> face property of `cursor-color'?  That would realize a face using the
> color from `cursor-color', right?  With your change, that won't update
> either if the face is changed.  Or at least I think so; what actually
> happens?

That sounds like a correct analysis, but I just tried it, and the
display is updated correctly...

Execute this in a fundamental buffer:

(progn
  (insert "\n12345\n")
  (add-text-properties (- (point) 6) (1- (point)) '(face cursor)))

Then execute this in the *scratch* buffer:

    (require 'cl)
    (loop for i from 0 to 501 by 1
          do (set-cursor-color (if (eq 1 (mod i 2))
                                "blue"
                              "red"))
          (sit-for 0))

Ok, the 12345 does not change color until the command completes, but I
think that's a very small problem  (the example is "constructed").

>
> If it's the way I expect, I think we should urge users not to do that,
> or else make it get an error, or else make it work.
>
>     Is it necessary to add anything to NEWS or the manuals about this ?
>
> It should tell people that they can't, or shouldn't, use certain faces
> in certain ways.  I don't think it needs to describe the mechanism
> such as the face-no-inherit property.

Is this ok?

Faces must not inherit from the `cursor' face.  If you do this, such
faces may not be correctly updated if you change the cursor face.

-- 
Kim F. Storm  http://www.cua.dk