bug#55207: 29.0.50; tab-bar-format-align-right only works correctly with monospace characters

bug#55207: 29.0.50; tab-bar-format-align-right only works correctly with monospace characters

[Daniel Semyonov via Bug reports for GNU Emacs, the Swiss army knife of text editors]

When a character using a variable pitch font or an image (I've only
tested this with XBM images) is displayed on the tab bar after
'tab-bar-format-align-right', the resulting text ends before the end of
the tab bar.

Exact recipe (assuming the default font for the tab bar is variable pitch):

1. $ emacs -Q
2. M-: (setq tab-bar-format '(tab-bar-format-align-right tab-bar-format-tabs tab-bar-separator))
3. M-x tab-bar-mode

After following these steps, the initial tab ends before the end
of the tab bar, and the gap grows with each additional tab.


In GNU Emacs 29.0.50 (build 10, x86_64-pc-linux-gnu, GTK+ Version 3.24.33, cairo version 1.16.0)
 of 2022-05-01 built on coldharbour
Repository revision: 5f220d9555a908dd9957afa27d168d74adf6c7df
Repository branch: master
Windowing system distributor 'The X.Org Foundation', version 11.0.12101003
System Description: Debian GNU/Linux bookworm/sid

Configured using:
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bug#55207: 29.0.50; tab-bar-format-align-right only works correctly with monospace characters

[Juri Linkov]

> When a character using a variable pitch font or an image (I've only
> tested this with XBM images) is displayed on the tab bar after
> 'tab-bar-format-align-right', the resulting text ends before the end of
> the tab bar.
>
> Exact recipe (assuming the default font for the tab bar is variable pitch):
>
> 1. $ emacs -Q
> 2. M-: (setq tab-bar-format '(tab-bar-format-align-right tab-bar-format-tabs tab-bar-separator))
> 3. M-x tab-bar-mode
>
> After following these steps, the initial tab ends before the end
> of the tab bar, and the gap grows with each additional tab.

Thanks for the bug report.  Indeed the property :align-to
in tab-bar-format-align-right fails to align to the proper width
when using a variable pitch font.  Unfortunately, I have no idea
how to fix this.

bug#55207: 29.0.50; tab-bar-format-align-right only works correctly with monospace characters

[Lars Ingebrigtsen]

Juri Linkov <juri@linkov.net> writes:

> Thanks for the bug report.  Indeed the property :align-to
> in tab-bar-format-align-right fails to align to the proper width
> when using a variable pitch font.  Unfortunately, I have no idea
> how to fix this.

I am completely unfamiliar with how the tar bar works, but -- can't you
just measure the widths of the elements with string-pixel-width or the
like and use that to compute the alignments?

-- 
(domestic pets only, the antidote for overdose, milk.)
   bloggy blog: http://lars.ingebrigtsen.no

bug#55207: 29.0.50; tab-bar-format-align-right only works correctly with monospace characters

[Juri Linkov]

> I am completely unfamiliar with how the tar bar works, but -- can't you
> just measure the widths of the elements with string-pixel-width or the
> like and use that to compute the alignments?

Thanks for the suggestion.  This works quite nicely.
Only a very small amount of pixels are still misaligned.

diff --git a/lisp/tab-bar.el b/lisp/tab-bar.el
index 03b49e9657..7896e051ab 100644
--- a/lisp/tab-bar.el
+++ b/lisp/tab-bar.el
@@ -915,8 +915,8 @@ tab-bar-format-align-right
   (let* ((rest (cdr (memq 'tab-bar-format-align-right tab-bar-format)))
          (rest (tab-bar-format-list rest))
          (rest (mapconcat (lambda (item) (nth 2 item)) rest ""))
-         (hpos (length rest))
-         (str (propertize " " 'display `(space :align-to (- right ,hpos)))))
+         (hpos (string-pixel-width rest))
+         (str (propertize " " 'display `(space :align-to (- right (,hpos))))))
     `((align-right menu-item ,str ignore))))

bug#55207: 29.0.50; tab-bar-format-align-right only works correctly with monospace characters

[Daniel Semyonov via Bug reports for GNU Emacs, the Swiss army knife of text editors]

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>>>>> Juri Linkov writes:

    > Thanks for the suggestion.  This works quite nicely.  Only a very
    > small amount of pixels are still misaligned.

Hi Juri and Lars,

This patch seems to almost completely remove the issue in the simple
case I reported.

However, in the more complicated configuration I actually use it doesn't
make much of a difference:

Before

[-- Attachment #2: before --]
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After

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(Both screen shots extend to the right end of the tab bar)

The icons on the mode line are small XBM images, the theme is Modus
Operandi.

bug#55207: 29.0.50; tab-bar-format-align-right only works correctly with monospace characters

[Juri Linkov]

> However, in the more complicated configuration I actually use it doesn't
> make much of a difference:
> ...
> The icons on the mode line are small XBM images, the theme is Modus
> Operandi.

I guess you are using global-mode-string with XBM images.
Could you then try something like this to see what number it returns?

(string-pixel-width (string-trim-right (format-mode-line global-mode-string)))

bug#55207: 29.0.50; tab-bar-format-align-right only works correctly with monospace characters

[Daniel Semyonov via Bug reports for GNU Emacs, the Swiss army knife of text editors]

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>>>>> Juri Linkov writes:

    > I guess you are using global-mode-string with XBM images.

I should've added this to the last message, but this is my tab bar
configuration (just a little bit over engineered):

(init-base-customize display-time-format "%H:%M %d/%m/%y"
                     display-time-mail-function #'ignore)
(display-time-mode)

(setq global-mode-string
      '(:eval
        `(""
          ,(and (boundp 'init-gnus-unread-mail-string)
                init-gnus-unread-mail-string)
          ,(and (boundp 'init-gnus-unread-news-string)
                init-gnus-unread-news-string)
          ,(and (boundp 'init-volume-string)
                init-volume-string)
          ,(and (boundp 'emms-mode-line-string)
                emms-mode-line-string)
          ,(and (boundp 'emms-playing-time-string)
                emms-playing-time-string)
          " | " ,(string-trim-right display-time-string))))
(init-base-customize tab-bar-format
                     '( tab-bar-format-tabs tab-bar-format-align-right
                        tab-bar-format-global))
(tab-bar-mode)


('init-base-customize' is just a convenience macro which calls
'customize-set-variable' under the hood and the value of 'init-*-string' is
a string of the form "x: y " where 'x' is a letter and 'y' is a number or
percentage; 'x:' is replaced with an XBM image using the 'display'
property on GUI frames).

    > Could you then try something like this to see what number it
    > returns?

I did some further testing, first adding arbitrary text to the
'global-mode-string', then adding more images and finally adding both.
I've attached screen shots of my full Emacs frame with an example of
each test case, taken right after evaluating your provided expression
(so the number is shown in the echo area).  The buffer shown in the
images shows the exact changes I made to the 'global-mode-string' in
each test.

I've also attached the envelope and volume icons seen in the screen
shots, just in case they may be useful.

Hopefully this information proves useful, thank you for looking into
this.


[-- Attachment #2: control --]
[-- Type: image/png, Size: 135538 bytes --]

[-- Attachment #3: added text --]
[-- Type: image/png, Size: 135443 bytes --]

[-- Attachment #4: added image --]
[-- Type: image/png, Size: 131180 bytes --]

[-- Attachment #5: added image and text --]
[-- Type: image/png, Size: 131534 bytes --]

[-- Attachment #6: volume icon --]
[-- Type: image/x-xbitmap, Size: 240 bytes --]

[-- Attachment #7: envelope icon --]
[-- Type: image/x-xbitmap, Size: 222 bytes --]

bug#55207: 29.0.50; tab-bar-format-align-right only works correctly with monospace characters

[Juri Linkov]

> Hopefully this information proves useful, thank you for looking into
> this.

Thanks, this helped to realize that the pixel width should be calculated
with the same face that is really used on the tab bar.  Could you please
try a new patch.  At least, I see that it works with your test cases.

diff --git a/lisp/tab-bar.el b/lisp/tab-bar.el
index 03b49e9657..4d5ec4098c 100644
--- a/lisp/tab-bar.el
+++ b/lisp/tab-bar.el
@@ -915,8 +915,8 @@ tab-bar-format-align-right
   (let* ((rest (cdr (memq 'tab-bar-format-align-right tab-bar-format)))
          (rest (tab-bar-format-list rest))
          (rest (mapconcat (lambda (item) (nth 2 item)) rest ""))
-         (hpos (length rest))
-         (str (propertize " " 'display `(space :align-to (- right ,hpos)))))
+         (hpos (string-pixel-width (propertize rest 'face 'tab-bar)))
+         (str (propertize " " 'display `(space :align-to (- right (,hpos))))))
     `((align-right menu-item ,str ignore))))

bug#55207: 29.0.50; tab-bar-format-align-right only works correctly with monospace characters

[Daniel Semyonov via Bug reports for GNU Emacs, the Swiss army knife of text editors]

>>>>> Juri Linkov writes:

    > Could you please try a new patch.  At least, I see that it works
    > with your test cases.

The new patch seems to completely fix the issue, thanks!