bug#57264: 29.0.50; Wrong xcursor colour when over an Emacs frame

bug#57264: 29.0.50; Wrong xcursor colour when over an Emacs frame

[Visuwesh]

When the mouse pointer is over an Emacs frame, the xcursor has the wrong
colour; this is not observed with other Xorg apps like okular,
libreoffice, ungoogled-chromium.

Emacs has no problem with the default Xorg cursor theme---it is black as
expected---but this happens when I use the xcursor theme from below.

To reproduce,

    1. Download and install the cursor theme from
       https://π.duncano.de/files/xcursor-plan9-0.2.tar.xz
    2. Launch emacs -Q as `XCURSOR_THEME=plan9 emacs -Q'.
    3. Move the cursor over the Emacs frame into a void area and observe
       the left pointer colour.  It is white here.
    4. Now repeat the same but for another application, the left pointer
       colour is black as expected.

Changing the mouse face's :background does not help.  It changes the
border colour.  If it gives any clue, I also see this problem with st.

Thanks.


In GNU Emacs 29.0.50 (build 2, x86_64-pc-linux-gnu, X toolkit, Xaw scroll bars)
 of 2022-08-15 built on astatine
Repository revision: d5ee49c25c8f59ab17c40eebdf38a769c2f5588b
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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XIM XINPUT2 XPM LUCID ZLIB
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bug#57264: 29.0.50; Wrong xcursor colour when over an Emacs frame

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

Visuwesh <visuweshm@gmail.com> writes:

> When the mouse pointer is over an Emacs frame, the xcursor has the wrong
> colour; this is not observed with other Xorg apps like okular,
> libreoffice, ungoogled-chromium.
>
> Emacs has no problem with the default Xorg cursor theme---it is black as
> expected---but this happens when I use the xcursor theme from below.
>
> To reproduce,
>
>     1. Download and install the cursor theme from
>        https://π.duncano.de/files/xcursor-plan9-0.2.tar.xz
>     2. Launch emacs -Q as `XCURSOR_THEME=plan9 emacs -Q'.
>     3. Move the cursor over the Emacs frame into a void area and observe
>        the left pointer colour.  It is white here.
>     4. Now repeat the same but for another application, the left pointer
>        colour is black as expected.
>
> Changing the mouse face's :background does not help.  It changes the
> border colour.  If it gives any clue, I also see this problem with st.
>
> Thanks.

Emacs is doing the right thing here, along with st, xterm, urxvt, et
cetera.  The bug lies in the other programs where the cursor is mostly
black with a white border.

bug#57264: 29.0.50; Wrong xcursor colour when over an Emacs frame

[Visuwesh]

[வியாழன் ஆகஸ்ட் 18, 2022] Po Lu via "Bug reports for GNU Emacs, the Swiss army knife of text editors" wrote:

> Emacs is doing the right thing here, along with st, xterm, urxvt, et
> cetera.  The bug lies in the other programs where the cursor is mostly
> black with a white border.

Almost every Xorg app I have (add mpv, sxiv and meh to the earlier list)
and the root window except st and Emacs shows the right cursor for me.
I'm using the awesome window manager here if it matters.

I could invert the image but that would make it worse on every other
Xorg app I use.

bug#57264: 29.0.50; Wrong xcursor colour when over an Emacs frame

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

Visuwesh <visuweshm@gmail.com> writes:

> Almost every Xorg app I have (add mpv, sxiv and meh to the earlier list)
> and the root window except st and Emacs shows the right cursor for me.

The cursor theme you sent does not include a replacement for the default
X cursor, so what is being displayed on the root window (given that the
window manager did not define another) is from the default cursor font,
not your cursor theme.  mpv also does not set a cursor, but inherits the
cursor from the frame window provided by the window manager.

I am not familar with the other programs, but I'm sure they use the
Xcursor library, which these days has various problems with non-ARGB
cursor bitmaps.  Emacs does not and thus behaves correctly.

> I'm using the awesome window manager here if it matters.

I'm not familiar with that window manager, sorry.

> I could invert the image but that would make it worse on every other
> Xorg app I use.

Or perhaps ask those other programs to call XRecolorCursor with the
right colors after loading a core cursor with the Xcursor library.

bug#57264: 29.0.50; Wrong xcursor colour when over an Emacs frame

[Visuwesh]

[வியாழன் ஆகஸ்ட் 18, 2022] Po Lu via "Bug reports for GNU Emacs, the Swiss army knife of text editors" wrote:

> Visuwesh <visuweshm@gmail.com> writes:
>
>> Almost every Xorg app I have (add mpv, sxiv and meh to the earlier list)
>> and the root window except st and Emacs shows the right cursor for me.
>
> The cursor theme you sent does not include a replacement for the default
> X cursor, so what is being displayed on the root window (given that the
> window manager did not define another) is from the default cursor font,
> not your cursor theme.

What is the default X cursor, anyway?  I thought it was XC_left_ptr [1]
and AFAICT, the theme does have left_ptr.

> mpv also does not set a cursor, but inherits the cursor from the frame
> window provided by the window manager.

I thought this would be the case in some of these programs.

> I am not familar with the other programs, but I'm sure they use the
> Xcursor library, which these days has various problems with non-ARGB
> cursor bitmaps.  Emacs does not and thus behaves correctly.
>
>> I'm using the awesome window manager here if it matters.
>
> I'm not familiar with that window manager, sorry.

I took a quick look and it seems to use xcb_cursor_load_cursor.
https://github.com/awesomeWM/awesome/blob/7a8fa9d27a7907ab81e60274c925ba65d10015aa/common/xcursor.c

>> I could invert the image but that would make it worse on every other
>> Xorg app I use.
>
> Or perhaps ask those other programs to call XRecolorCursor with the
> right colors after loading a core cursor with the Xcursor library.

Unfortunately, that would be a huge undertaking.

bug#57264: 29.0.50; Wrong xcursor colour when over an Emacs frame

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

Visuwesh <visuweshm@gmail.com> writes:

> [வியாழன் ஆகஸ்ட் 18, 2022] Po Lu via "Bug reports for GNU Emacs, the Swiss army knife of text editors" wrote:
>
>> Visuwesh <visuweshm@gmail.com> writes:
>>
>>> Almost every Xorg app I have (add mpv, sxiv and meh to the earlier list)
>>> and the root window except st and Emacs shows the right cursor for me.
>>
>> The cursor theme you sent does not include a replacement for the default
>> X cursor, so what is being displayed on the root window (given that the
>> window manager did not define another) is from the default cursor font,
>> not your cursor theme.

> What is the default X cursor, anyway?  I thought it was XC_left_ptr [1]
> and AFAICT, the theme does have left_ptr.

The default X cursor is XC_X_cursor (x-pointer-X-cursor in Emacs.)

> I took a quick look and it seems to use xcb_cursor_load_cursor.
> https://github.com/awesomeWM/awesome/blob/7a8fa9d27a7907ab81e60274c925ba65d10015aa/common/xcursor.c

Right, I think that's also problematic (compared to XCreateFontCursor.)

bug#57264: 29.0.50; Wrong xcursor colour when over an Emacs frame

[Visuwesh]

[வெள்ளி ஆகஸ்ட் 19, 2022] Po Lu wrote:

> Visuwesh <visuweshm@gmail.com> writes:
>
>> [வியாழன் ஆகஸ்ட் 18, 2022] Po Lu via "Bug reports for GNU Emacs, the Swiss army knife of text editors" wrote:
>>
>>> Visuwesh <visuweshm@gmail.com> writes:
>>>
>>>> Almost every Xorg app I have (add mpv, sxiv and meh to the earlier list)
>>>> and the root window except st and Emacs shows the right cursor for me.
>>>
>>> The cursor theme you sent does not include a replacement for the default
>>> X cursor, so what is being displayed on the root window (given that the
>>> window manager did not define another) is from the default cursor font,
>>> not your cursor theme.

[ BTW, my window manager shows the left_ptr.  ]

>> What is the default X cursor, anyway?  I thought it was XC_left_ptr [1]
>> and AFAICT, the theme does have left_ptr.
>
> The default X cursor is XC_X_cursor (x-pointer-X-cursor in Emacs.)

Thanks.  But do you know why I am seeing this behaviour?  I cannot see
what is wrong with the theme.  Supposedly, the input to the xcursorgen
program and the image files are good.  I opened the generated Xcursor
file in GIMP and it is also of the expected colours.  I am unfortunately
lost and I would be really grateful if you can give any pointers.

BTW, all this made me think: why not let the user set the foreground
colour of the cursor, via the mouse face, too?  This would at least
solve my problem immediately despite being an awful hack.

bug#57264: 29.0.50; Wrong xcursor colour when over an Emacs frame

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

Visuwesh <visuweshm@gmail.com> writes:

> Thanks.  But do you know why I am seeing this behaviour?  I cannot see
> what is wrong with the theme.  Supposedly, the input to the xcursorgen
> program and the image files are good.  I opened the generated Xcursor
> file in GIMP and it is also of the expected colours.  I am unfortunately
> lost and I would be really grateful if you can give any pointers.

The Xcursor library doesn't set foreground and background colors for
core cursors by default, and the application didn't set them either.

> BTW, all this made me think: why not let the user set the foreground
> colour of the cursor, via the mouse face, too?  This would at least
> solve my problem immediately despite being an awful hack.

I think that would work.  I will work on it but it may or may not take a
while depending on how busy I am in the next several days.

bug#57264: 29.0.50; Wrong xcursor colour when over an Emacs frame

[Visuwesh]

[வெள்ளி ஆகஸ்ட் 19, 2022] Po Lu via "Bug reports for GNU Emacs, the Swiss army knife of text editors" wrote:

> Visuwesh <visuweshm@gmail.com> writes:
>
>> Thanks.  But do you know why I am seeing this behaviour?  I cannot see
>> what is wrong with the theme.  Supposedly, the input to the xcursorgen
>> program and the image files are good.  I opened the generated Xcursor
>> file in GIMP and it is also of the expected colours.  I am unfortunately
>> lost and I would be really grateful if you can give any pointers.
>
> The Xcursor library doesn't set foreground and background colors for
> core cursors by default, and the application didn't set them either.

I see, thanks.

>> BTW, all this made me think: why not let the user set the foreground
>> colour of the cursor, via the mouse face, too?  This would at least
>> solve my problem immediately despite being an awful hack.
>
> I think that would work.  I will work on it but it may or may not take a
> while depending on how busy I am in the next several days.

There's no rush, thanks for all the work you do!