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bug#28771: 26.0.60; A couple space display property feature requests
From: |
Alex |
Subject: |
bug#28771: 26.0.60; A couple space display property feature requests |
Date: |
Tue, 10 Oct 2017 11:54:41 -0600 |
User-agent: |
Gnus/5.13 (Gnus v5.13) Emacs/26.0.60 (gnu/linux) |
Eli Zaretskii <eliz@gnu.org> writes:
>> From: Alex <agrambot@gmail.com>
>> Date: Mon, 09 Oct 2017 18:20:42 -0600
>>
>> 1. Specifying the pixel width to the left/center/right of the text area.
>> This is helpful (I believe it's necessary if I want it to be robust)
>> when one wants to pad either side of a string with the same number of
>> pixels and the left side uses (:align-to 0).
>>
>> I could use (:width (+ left-fringe left-margin)) for the right
>> padding, but this doesn't take into account line-number display, as
>> well as the scroll-bar width (if it's on the left).
>>
>> 2. Specifying the pixel position relative to the left or right edge of
>> the window. The right edge of the window currently may be the right
>> edge of the right fringe or the scroll bar, depending on what side it
>> is on. Also, just in the case that in the future the
>> fringe/scroll-bar may not be the outermost elements, there should be
>> a way to explicitly specify one of the edges.
>
> These two requests are no in the original message, and I admit I don't
> really understand the situations they describe. Can you elaborate
> about them, preferably with an example that shows what is currently
> possible and an explanation why the current capabilities are
> insufficient? (Yes, I've seen the patches you propose, but I still
> would like to understand the problems better.)
Right, they're additions that I felt should go directly to a bug report.
1. There is currently no robust way to specify a pixel width to the
center or left/right edge of the text area in the 'space' display spec.
This is because there's no way to tell what's before the left edge of
the text area. If there's a left-side scroll-bar, then its width
should be included; but if it's on the right, its width shouldn't be.
:align-to currently allows for this calculation, but :width doesn't.
The diff adds the same calculation to :width.
As for an example, try this in a graphical emacs -Q:
(setq header-line-format
(propertize
(concat (propertize " "
'display
'(space :align-to 0))
"Test"
(propertize " "
'display
'(space :width (+ left-fringe left-margin))))
'face 'highlight))
By default, the spaces before and after test are equally sized. Even
if you disable fringe-mode or enable margins (e.g. linum-mode), the
spaces are equal. However, try setting the scroll-bar to appear on
the left. Now, the left space is noticeably bigger than the right.
Changing the last space's :width spec to be '(+ left-fringe
left-margin scroll-bar)' will now make the spaces equal with a left
scroll-bar, but unequal with a right scroll-bar.
If you apply my diff and change the second space's :width spec to be
'left', then it is correct in both cases.
I don't know of a good use-case for :width center or :width right,
but I figured that for completeness I might as well implement them.
2. Suppose you want to align a string to the right edge of the window. I
couldn't find a way to do this currently since there's no guarantee
what elements are on the left/right edges. Try:
(setq header-line-format
(concat (propertize " "
'display
'(space :align-to (- (+ scroll-bar
scroll-bar)
4)))
"Test"))
This works if there's a right scroll-bar (or if there's none, oddly
enough), but not if there's a left scroll-bar. Replacing `scroll-bar'
with `right-fringe' doesn't work if there's a right scroll-bar.
Replacing the :align-to spec with `right-edge' works in all cases.
A similar argument can be made for aligning from the left edge.
>> 3. Following from "1." and the help-gnu-emacs thread, it would be nice
>> if there was a display property that allowed you to pad a string on
>> both sides with a pixel-specified space instead of surrounding it
>> with 2 pixel-specified spaces.
>
> I replied on help-gnu-emacs. In a nutshell, the 'space' display spec
> is a replacing spec, so it cannot be easily used on non-space text.
> You could probably have a before-string whose value is a space with
> the 'space' display spec, if that makes any difference.
Can you put overlays in the header-line? That's my use-case at the
moment.
> use the space-width spec, as described on help-gnu-emacs.
I believe in my case (since the text may contain spaces), that's
equivalent to just the :width spec on the first/last spaces.
#3 is just a convenience request -- it makes dealing with pixel-spaces a
bit easier, but as long as #1 is implemented then I don't think it bring
any new functionality.
Is there currently no display spec that allows for appending/prepending
(or would it be hard to add)? If so, then #3 can be ignored.