> That was because of performance issues, right?  I see nothing in that
 > discussion that objects to the character-level dragging in principle.
 >
 > I see no reason not to allow that as an option.  Patches welcome.

I attach a patch supposed to fix your earlier

  According to the manual, window-resize-pixelwise = nil is what you
  want.  However, it currently doesn't affect dragging the window border
  with the mouse, AFAIU.  Martin, am I right?  This could be a simple
  omission.

But it's still sluggish as back in 2014, the mouse cursor moves far
ahead of the lines to drag and it refuses to move a mode line with
'mouse-fine-grained-tracking' non-nil.  Likely remember_mouse_glyph
interferes here.

martin