From mboxrd@z Thu Jan 1 00:00:00 1970 Path: news.gmane.org!.POSTED!not-for-mail From: Alan Mackenzie Newsgroups: gmane.emacs.bugs Subject: bug#32874: Unwanted scrolling in edebug `f' command when follow-mode is active Date: Mon, 1 Oct 2018 12:59:22 +0000 Message-ID: <20181001125922.GC5947@ACM> References: <20180929140957.GB5008@ACM> <83lg7k5q2o.fsf@gnu.org> <20180929153729.GD5008@ACM> <83h8i85lr7.fsf@gnu.org> <20180929204113.GF5008@ACM> <837ej35tex.fsf@gnu.org> <20180930153646.GF6305@ACM> <83in2m52h1.fsf@gnu.org> NNTP-Posting-Host: blaine.gmane.org Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii X-Trace: blaine.gmane.org 1538399052 29613 195.159.176.226 (1 Oct 2018 13:04:12 GMT) X-Complaints-To: usenet@blaine.gmane.org NNTP-Posting-Date: Mon, 1 Oct 2018 13:04:12 +0000 (UTC) User-Agent: Mutt/1.10.1 (2018-07-13) Cc: 32874@debbugs.gnu.org To: Eli Zaretskii Original-X-From: bug-gnu-emacs-bounces+geb-bug-gnu-emacs=m.gmane.org@gnu.org Mon Oct 01 15:04:07 2018 Return-path: Envelope-to: geb-bug-gnu-emacs@m.gmane.org Original-Received: from lists.gnu.org ([208.118.235.17]) by blaine.gmane.org with esmtp (Exim 4.84_2) (envelope-from ) id 1g6xrr-0007ZT-98 for geb-bug-gnu-emacs@m.gmane.org; Mon, 01 Oct 2018 15:04:07 +0200 Original-Received: from localhost ([::1]:38566 helo=lists.gnu.org) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1g6xtx-00067u-R9 for geb-bug-gnu-emacs@m.gmane.org; Mon, 01 Oct 2018 09:06:17 -0400 Original-Received: from eggs.gnu.org ([2001:4830:134:3::10]:53202) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1g6xtm-00067e-2N for bug-gnu-emacs@gnu.org; Mon, 01 Oct 2018 09:06:12 -0400 Original-Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1g6xti-0002yS-LF for bug-gnu-emacs@gnu.org; Mon, 01 Oct 2018 09:06:06 -0400 Original-Received: from debbugs.gnu.org ([208.118.235.43]:56594) by eggs.gnu.org with esmtps (TLS1.0:RSA_AES_128_CBC_SHA1:16) (Exim 4.71) (envelope-from ) id 1g6xti-0002y4-FZ for bug-gnu-emacs@gnu.org; Mon, 01 Oct 2018 09:06:02 -0400 Original-Received: from Debian-debbugs by debbugs.gnu.org with local (Exim 4.84_2) (envelope-from ) id 1g6xti-0001Fg-6V for bug-gnu-emacs@gnu.org; Mon, 01 Oct 2018 09:06:02 -0400 X-Loop: help-debbugs@gnu.org Resent-From: Alan Mackenzie Original-Sender: "Debbugs-submit" Resent-CC: bug-gnu-emacs@gnu.org Resent-Date: Mon, 01 Oct 2018 13:06:02 +0000 Resent-Message-ID: Resent-Sender: help-debbugs@gnu.org X-GNU-PR-Message: followup 32874 X-GNU-PR-Package: emacs X-GNU-PR-Keywords: Original-Received: via spool by 32874-submit@debbugs.gnu.org id=B32874.15383991104728 (code B ref 32874); Mon, 01 Oct 2018 13:06:02 +0000 Original-Received: (at 32874) by debbugs.gnu.org; 1 Oct 2018 13:05:10 +0000 Original-Received: from localhost ([127.0.0.1]:60852 helo=debbugs.gnu.org) by debbugs.gnu.org with esmtp (Exim 4.84_2) (envelope-from ) id 1g6xsr-0001EA-ON for submit@debbugs.gnu.org; Mon, 01 Oct 2018 09:05:10 -0400 Original-Received: from colin.muc.de ([193.149.48.1]:41379 helo=mail.muc.de) by debbugs.gnu.org with smtp (Exim 4.84_2) (envelope-from ) id 1g6xsq-0001E2-9u for 32874@debbugs.gnu.org; Mon, 01 Oct 2018 09:05:08 -0400 Original-Received: (qmail 77859 invoked by uid 3782); 1 Oct 2018 13:05:07 -0000 Original-Received: from acm.muc.de (p5B1474A3.dip0.t-ipconnect.de [91.20.116.163]) by colin.muc.de (tmda-ofmipd) with ESMTP; Mon, 01 Oct 2018 15:05:06 +0200 Original-Received: (qmail 6523 invoked by uid 1000); 1 Oct 2018 12:59:22 -0000 Content-Disposition: inline In-Reply-To: <83in2m52h1.fsf@gnu.org> X-Delivery-Agent: TMDA/1.1.12 (Macallan) X-Primary-Address: acm@muc.de X-BeenThere: debbugs-submit@debbugs.gnu.org X-Mailman-Version: 2.1.18 Precedence: list X-detected-operating-system: by eggs.gnu.org: GNU/Linux 2.2.x-3.x [generic] X-Received-From: 208.118.235.43 X-BeenThere: bug-gnu-emacs@gnu.org List-Id: "Bug reports for GNU Emacs, the Swiss army knife of text editors" List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Errors-To: bug-gnu-emacs-bounces+geb-bug-gnu-emacs=m.gmane.org@gnu.org Original-Sender: "bug-gnu-emacs" Xref: news.gmane.org gmane.emacs.bugs:150869 Archived-At: Hello, Eli. On Sun, Sep 30, 2018 at 20:17:46 +0300, Eli Zaretskii wrote: > > Date: Sun, 30 Sep 2018 15:36:46 +0000 > > Cc: 32874@debbugs.gnu.org > > From: Alan Mackenzie > > > > I've had a look at window-scroll-functions, but I can't see what you > > > > must be seeing. Currently, the documentation warns against trying to > > > > influence the scrolling, saying "it probably won't work anyway". > > > But you don't want to scroll yourself, you just want to switch the > > > selected window and move point so that Emacs won't need to scroll. > > > AFAIU, follow-mode wants to kick in when point goes off the selected > > > window. And the call to window-scroll-functions is exactly the place > > > where the display engine decides it needs to scroll the window, but > > > didn't actually scroll it yet. So that looks like a good place to have > > > follow-mode do its thing. We might need to add some simple facility > > > for follow-mode to use, so that it could signal the display engine not > > > to scroll the window. Other than that, I think this possibility is > > > worth exploring. > > Follow-mode also needs to be active on explicit scrolling commands such > > as C-v. Also, after inserting a newline, subsequent windows need to be > > scrolled down. After either of these, follow-mode laboriously starts > > determining where all its windows have to start and end. There's nothing > > in the display engine to help in this process. > I'm not sure you are right, since all of the situations you describe > go through the function try_scrolling, which calls > window-scroll-functions. I have the feeling we're at cross purposes somehow, here. I think the display engine, by itself, is only ever going to be scrolling the selected window. Some mechanism is needed for scrolling the other follow windows to synchronise with the selected window. Currently, follow-mode does all this calculation, neither elegantly nor efficiently. I don't think there is anything in the display manager to help with this. Are you suggesting that the scrolling of the other follow windows could somehow be assisted, possibly even triggered, by a call of window-scroll-functions from the selected window? > > > > Maybe it would be relatively simple to introduce new functionality. > > > > Something like "scroll window so that window-end gets the given value". > > > I'm not sure I understand how this could help follow-mode. Please > > > elaborate. > > Currently when a middle or right hand window gets scrolled for any > > reason, follow-mode has to determine how to scroll windows to the left of > > it. It does this by making a first guess at a window-start, does > > set-window-start, then moves forward through the window to see how close > > window-end is to where it needs to be. If it's a line off, a different > > starting position is chosen, and so on, until window-start gets correctly > > placed. > > If there were a function set-window-end, the display engine itself could > > move back over the text lines to find window-start far more efficiently > > and directly than follow-mode can. > It should be very easy to write such a function, provided that you can > pass it as argument the buffer position of the beginning of the last > line in the window (not the end of that line). That sounds very strange. Where would the difficulty lie in the display engine doing (forward-line -1) rather than the Lisp code? -- Alan Mackenzie (Nuremberg, Germany).