Re: master 77c3d41adc: Prevent text decorations from overwriting surrounding areas on X

[Eli Zaretskii]

> From: Po Lu <luangruo@yahoo.com>
> Date: Mon, 10 Jan 2022 19:58:12 +0800
> 
> Po Lu via Mailing list for Emacs changes <emacs-diffs@gnu.org> writes:
> 
> >     Prevent text decorations from overwriting surrounding areas on X
> >     
> >     * src/xterm.c (x_draw_underwave): New parameter
> >     `decoration_width'.
> >     (x_draw_glyph_string): Constrain decoration width to current
> >     text area.
> 
> This happens on X because nothing actually clips the decoration to the
> string's area when we draw the decoration.

I'm not sure I understand what clipping did you have in mind.  In
x_draw_underwave, for example, we have this:

  /* Find and set clipping rectangle */

  wave_clip.x = x0;
  wave_clip.y = y0;
  wave_clip.width = width;
  wave_clip.height = wave_height;
  get_glyph_string_clip_rect (s, &string_clip);

  if (!gui_intersect_rectangles (&wave_clip, &string_clip, &final_clip))
    return;

  XSetClipRectangles (display, s->gc, 0, 0, &final_clip, 1, Unsorted);

Isn't this the clipping?  Or what am I missing?

> You can test by running custom-set-faces on default, enabling an
> underline or overline, and typing in a field that is extended to the end
> of the line.

Please show some actual Lisp to try this, so we wouldn't need to guess
whether the problem doesn't exist or we failed to reproduce correctly.