bug#47581: 27.1; tab-bar missed mouse clicks on MS-Windows

[Eli Zaretskii <eliz@gnu.org>]

> From: Ioannis Kappas <ioannis.kappas@gmail.com>
> Date: Sun, 4 Apr 2021 20:49:24 +0100
> Cc: juri@linkov.net, 47581@debbugs.gnu.org
> 
>  I think the actual problem is elsewhere: in handle_tab_bar_click.  It
>  includes code that was copied from handle_tool_bar_click, and which
>  pays attention to the value of mouse-highlight.  But tab-bar buttons
>  don't behave like tool-bar buttons in this regard: they don't respond
>  to moving the mouse pointer to them by "activating" the button.  So I
>  think that code should be removed from handle_tab_bar_click.  To wit:
>  turn mouse-highlight off (M-x set-variable RET mouse-highlight RET nil
>  RET), and clicks on tab-bar buttons miraculously start working with
>  100% reliability.
> 
> This will indeed also solve the problem by removing the comparison in
> B.1.1 which is using the potentially stale
> src/frame.h:MOUSE_HL_INFO, which to me seems to be the source of the
> problem. And it is an even better solution, since that part of the
> code might have been included there only by mistake. Nice catch!

This should now be fixed on the master branch.

> Regardless of this though, assuming the above sketch is correct,
> shouldn't we also consider fixing the code in
> src/xdisp.c:remember_mouse_glyph so as to set the
> src/w32term.h:FRAME_DISPLAY_INFO's `last_mouse_glyph' using
> `text-glyph' coordinates, so as for A.1.1 to fire up based on the actual tab-bar
> glyph coordinates during a mouse move (so that MOUSE_HL_INFO does not
> contain stale information)? I can't think of a reason why we might want this to 
> be set using virtual-glyph coords when over the tab-bar (but then, I can only see some of 
> the pieces and not the whole picture as you do).

If you can show some scenario where this causes real problems, I will
look into it.  In my testing, I saw no problems, and the coordinates I
saw weren't wrong, in the sense that they missed some glyphs due to
problems with glyph dimensions.