Re: master 5b5608c614: Fix glyph skipping optimization when a tab line is enabled

[Po Lu]

Eli Zaretskii <eliz@gnu.org> writes:

>> Author:     Po Lu <luangruo@yahoo.com>
>> AuthorDate: Mon Apr 18 13:23:23 2022 +0800
>> Commit:     Po Lu <luangruo@yahoo.com>
>> CommitDate: Mon Apr 18 13:23:23 2022 +0800
>> 
>>     Fix glyph skipping optimization when a tab line is enabled
>> 
>>     * src/dispnew.c (update_text_area): Compute vpos of header line
>>     correctly when window has tab line.
>> 
>> diff --git a/src/dispnew.c b/src/dispnew.c
>> index 0d95904..3cfe1b8 100644
>> --- a/src/dispnew.c
>> +++ b/src/dispnew.c
>> @@ -3928,9 +3928,12 @@ update_text_area (struct window *w, struct glyph_row 
>> *upd
>>          However, it causes excessive flickering when mouse is moved
>>          across the mode line.  Luckily, turning it off for the mode
>>          line doesn't seem to hurt anything. -- cyd.
>> -         But it is still needed for the header line. -- kfs.  */
>> +         But it is still needed for the header line. -- kfs.
>> +         The header line vpos is 1 if a tab line is enabled.  (18th
>> +         Apr 2022) */
>>        || (current_row->mouse_face_p
>> -         && !(current_row->mode_line_p && vpos > 0))
>> +         && !(current_row->mode_line_p
>> +              && (vpos > w->current_matrix->tab_line_p)))
>>        || current_row->x != desired_row->x)
>>      {
>>        output_cursor_to (w, vpos, 0, desired_row->y, desired_row->x);
>
> I'm not sure I understand this change.  What exactly is the problem,
> and how to reproduce it?  What if there's no header-line, but there is
> a tab-line, or vice versa, or both are displayed?

Not sure, but the previous code would also trigger for just tab lines,
but not also the header line if there was a tab line.

Here is how to reproduce the problem this fixes: turn on
global-tab-line-mode, open Info, type "m cl RET g Predicates RET", then
click on the "e" in the "Next: Control Structure" link on the header
line.  "Next:" will continue to be displayed in the mouse face even
though the mouse is no longer on any link, due to the "glyph-skipping"
optimization that is normally disabled for the header and tab lines
being used.

Thanks.