Subject: Re: bug#35740: 26.1; scroll bar jaggies / tearing

From: Noam Postavsky <[email-masked]>
Date: Sat, 25 May 2019 17:03:59 -0400

retitle 35740 [gtk] scroll bar jaggies / tearing
severity 35740 minor
tags 35740 + confirmed
quit

Bob Hepple <[email-masked]> writes:

> When I drift the sprite (mouse cursor) in and out of emacs the scroll
> bar goes a little bit crazy with animated jaggies running up and down
> its length.

>     the problem is resolved with emacs compiled with the athena/motif
>     or lucid toolkits

Yeah, after building with gtk I see this too.

> While an extremely minor annoyance, it remains irritating and shows
> emacs in a bad light. Is it possible that emacs is doing something weird
> / sophisticated with the scroll bar?

I don't think Emacs is doing anything especially weird with the
scrollbar.  There is a comment in xg_finish_scroll_bar_creation
(src/gtkutil.c) which seems related:

  /* The scroll bar widget does not draw on a window of its own.  Instead
     it draws on the parent window, in this case the edit widget.  So
     whenever the edit widget is cleared, the scroll bar needs to redraw
     also, which causes flicker.  Put an event box between the edit widget
     and the scroll bar, so the scroll bar instead draws itself on the
     event box window.  */