bug#39098: 26.3; bug of mouse-face including linebreak

bug#39098: 26.3; bug of mouse-face including linebreak

[ynyaaa]

If 'mouse-face is put on a reaion including linebreaks and active,
the appearance of the blank areas right to linebreaks is changed.
But pointing the blank areas does not activate 'mouse-face.

If 'mouse-face is put on a region ending with a linebreak,
the activated appearance covers the first character of the next line.

Example:
Evaluating the form below, a green area is displayed, where 'face,
'mouse-face, 'keymap and 'help-echo properties are put.
The green area includes a text "TARGET" and a blank area.

When pointing "TARGET", 'mouse-face is active.
The red area covers "*" in the next line, which has no properties.
When pointting the green blank area, 'mouse-face is not active.

Clicking the green area(both "TARGET" and the blank area) shows a
message "mouse-face: (:background red)".
The keymap is also active at "*" in the next line, which has no
properties.

The 'help-echo property is active only when pointing on "TARGET", not on
the green blank area.

(let ((map (make-sparse-keymap)))
  (switch-to-buffer (generate-new-buffer "tmp"))
  (define-key map [down-mouse-1] #'ignore)
  (define-key map [mouse-1]
    (lambda (ev)
      (interactive "e")
      (let* ((p (posn-point (event-end ev)))
             (prop (get-text-property p 'mouse-face)))
        (message "mouse-face: %s" prop))))
  (define-key map "e" 'end-of-line)
  (insert "before\n"
          (propertize "TARGET\n"
                      'face '(:background "green")
                      'mouse-face '(:background "red")
                      'help-echo "click here"
                      'keymap map)
        "*after\n"))



In GNU Emacs 26.3 (build 1, x86_64-w64-mingw32)
 of 2019-08-29 built on CIRROCUMULUS
Repository revision: 96dd0196c28bc36779584e47fffcca433c9309cd
Windowing system distributor 'Microsoft Corp.', version 6.3.9600
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bug#39098: 26.3; bug of mouse-face including linebreak

[Eli Zaretskii]

tags 39098 notabug
thanks

> From: ynyaaa@gmail.com
> Date: Sun, 12 Jan 2020 22:32:31 +0900
> 
> If 'mouse-face is put on a reaion including linebreaks and active,
> the appearance of the blank areas right to linebreaks is changed.
> But pointing the blank areas does not activate 'mouse-face.
> 
> If 'mouse-face is put on a region ending with a linebreak,
> the activated appearance covers the first character of the next line.

This is not a bug, this is how mouse-face is supposed to work.  It
differs from other faces in this regard, because it is intended to be
used to show mouse-sensitive text, including text that spans multiple
lines.

bug#39098: 26.3; bug of mouse-face including linebreak

[ynyaaa]

Eli Zaretskii <eliz@gnu.org> writes:

> tags 39098 notabug
> thanks
>
>> From: ynyaaa@gmail.com
>> Date: Sun, 12 Jan 2020 22:32:31 +0900
>> 
>> If 'mouse-face is put on a reaion including linebreaks and active,
>> the appearance of the blank areas right to linebreaks is changed.
>> But pointing the blank areas does not activate 'mouse-face.
>> 
>> If 'mouse-face is put on a region ending with a linebreak,
>> the activated appearance covers the first character of the next line.
>
> This is not a bug, this is how mouse-face is supposed to work.  It
> differs from other faces in this regard, because it is intended to be
> used to show mouse-sensitive text, including text that spans multiple
> lines.

Why is the out-of-range character highlighted only if it is at the
beginning of line?

bug#39098: 26.3; bug of mouse-face including linebreak

[Eli Zaretskii]

On January 13, 2020 8:53:07 AM GMT+02:00, ynyaaa@gmail.com wrote:
> 
> Why is the out-of-range character highlighted only if it is at the
> beginning of line?

Because you've covered the newline with mouse-face.  Newlines leave no glyphs on display, so the next character gets highlighted instead.  If you don't want this, exclude the newline from the mouse-face propertized part, it is unnecessary anyway, because a newline can never be "mouse-sensitive".

bug#39098: 26.3; bug of mouse-face including linebreak

[ynyaaa]

Eli Zaretskii <eliz@gnu.org> writes:

> On January 13, 2020 8:53:07 AM GMT+02:00, ynyaaa@gmail.com wrote:
>> 
>> Why is the out-of-range character highlighted only if it is at the
>> beginning of line?
>
> Because you've covered the newline with mouse-face.  Newlines leave no
> glyphs on display, so the next character gets highlighted instead.  If
> you don't want this, exclude the newline from the mouse-face
> propertized part, it is unnecessary anyway, because a newline can
> never be "mouse-sensitive".

Conversely, is there any way to disable 'mouse-face hilighting at blank
areas when the region contains more than two lines?
Just like 'underline face does not draw line to the right edge.

bug#39098: 26.3; bug of mouse-face including linebreak

[Eli Zaretskii]

> From: ynyaaa@gmail.com
> Cc: 39098@debbugs.gnu.org
> Date: Mon, 13 Jan 2020 23:44:51 +0900
> 
> Conversely, is there any way to disable 'mouse-face hilighting at blank
> areas when the region contains more than two lines?
> Just like 'underline face does not draw line to the right edge.

Maybe, I will need to check.  (Btw, the highlighting affects the empty
space past EOL only if you specify the background color; if you
specify 'underline' or something similar, it doesn't affect the empty
space.)

Suggest to file a feature-request bug report about that.

bug#39098: 26.3; bug of mouse-face including linebreak

[Stefan Kangas]

Eli Zaretskii <eliz@gnu.org> writes:

> tags 39098 notabug
> thanks
>
>> From: ynyaaa@gmail.com
>> Date: Sun, 12 Jan 2020 22:32:31 +0900
>> 
>> If 'mouse-face is put on a reaion including linebreaks and active,
>> the appearance of the blank areas right to linebreaks is changed.
>> But pointing the blank areas does not activate 'mouse-face.
>> 
>> If 'mouse-face is put on a region ending with a linebreak,
>> the activated appearance covers the first character of the next line.
>
> This is not a bug, this is how mouse-face is supposed to work.  It
> differs from other faces in this regard, because it is intended to be
> used to show mouse-sensitive text, including text that spans multiple
> lines.

I'm therefore also closing this bug.

Best regards,
Stefan Kangas