bug#38013: [PATCH] Rectangular region selection with mouse

[Eli Zaretskii]

> From: Mattias Engdegård <mattiase@acm.org>
> Date: Sun, 10 Nov 2019 14:49:11 +0100
> Cc: rudalics@gmx.at, 38013@debbugs.gnu.org
> 
> Or even simpler: assuming that STRETCH_GLYPHS are mostly tabs, we can treat 
> them as image glyphs for 'remember_mouse_glyph' purposes. What about:
> 
> --- a/src/xdisp.c
> +++ b/src/xdisp.c
> @@ -2572,7 +2572,7 @@ remember_mouse_glyph (struct frame *f, int gx, int gy, 
> NativeRectangle *rect)
>  
>         if (g < end)
>           {
> -           if (g->type == IMAGE_GLYPH)
> +           if (g->type == IMAGE_GLYPH || g->type == STRETCH_GLYPH)

Sorry for a late response.

Did you try this with stretch glyphs generated by the likes of
:align-to display 'space' properties?  Also, what about stretch glyphs
generated by the display engine in R2L screen lines (you can get those
easily by visiting TUTORIAL.he: each line that has white space at its
left end has a stretch glyph there)?

IOW, it might be necessary to add more conditions here, and just the
mouse_movement_in_tab thingy you added in a later version might not be
enough.  E.g., we may need a condition that verifies that this is a
TAB (should be easy by looking at glyph->object, I think).