From mboxrd@z Thu Jan 1 00:00:00 1970 Path: news.gmane.org!not-for-mail From: Alan Mackenzie Newsgroups: gmane.emacs.devel Subject: Re: "... the window start at a meaningless point within a line." Date: Thu, 1 Oct 2015 09:41:38 +0000 Message-ID: <20151001094138.GA2515@acm.fritz.box> References: <20150930204513.GA3174@acm.fritz.box> <83mvw39dp3.fsf@gnu.org> NNTP-Posting-Host: plane.gmane.org Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii X-Trace: ger.gmane.org 1443711217 2408 80.91.229.3 (1 Oct 2015 14:53:37 GMT) X-Complaints-To: usenet@ger.gmane.org NNTP-Posting-Date: Thu, 1 Oct 2015 14:53:37 +0000 (UTC) Cc: emacs-devel@gnu.org To: Eli Zaretskii Original-X-From: emacs-devel-bounces+ged-emacs-devel=m.gmane.org@gnu.org Thu Oct 01 16:53:28 2015 Return-path: Envelope-to: ged-emacs-devel@m.gmane.org Original-Received: from lists.gnu.org ([208.118.235.17]) by plane.gmane.org with esmtp (Exim 4.69) (envelope-from ) id 1ZhfEb-00023F-95 for ged-emacs-devel@m.gmane.org; Thu, 01 Oct 2015 16:53:25 +0200 Original-Received: from localhost ([::1]:51250 helo=lists.gnu.org) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1ZhfEa-0003GO-N6 for ged-emacs-devel@m.gmane.org; Thu, 01 Oct 2015 10:53:24 -0400 Original-Received: from eggs.gnu.org ([2001:4830:134:3::10]:41175) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1ZhaLc-0006KL-KQ for emacs-devel@gnu.org; Thu, 01 Oct 2015 05:40:23 -0400 Original-Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1ZhaLU-0006UC-Bp for emacs-devel@gnu.org; Thu, 01 Oct 2015 05:40:20 -0400 Original-Received: from mail.muc.de ([193.149.48.3]:10283) by eggs.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1ZhaLT-0006Ru-Vv for emacs-devel@gnu.org; Thu, 01 Oct 2015 05:40:12 -0400 Original-Received: (qmail 72577 invoked by uid 3782); 1 Oct 2015 09:40:10 -0000 Original-Received: from acm.muc.de (p5B14722A.dip0.t-ipconnect.de [91.20.114.42]) by colin.muc.de (tmda-ofmipd) with ESMTP; Thu, 01 Oct 2015 11:40:09 +0200 Original-Received: (qmail 2591 invoked by uid 1000); 1 Oct 2015 09:41:38 -0000 Content-Disposition: inline In-Reply-To: <83mvw39dp3.fsf@gnu.org> User-Agent: Mutt/1.5.23 (2014-03-12) X-Delivery-Agent: TMDA/1.1.12 (Macallan) X-Primary-Address: acm@muc.de X-detected-operating-system: by eggs.gnu.org: FreeBSD 9.x X-Received-From: 193.149.48.3 X-BeenThere: emacs-devel@gnu.org X-Mailman-Version: 2.1.14 Precedence: list List-Id: "Emacs development discussions." List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Errors-To: emacs-devel-bounces+ged-emacs-devel=m.gmane.org@gnu.org Original-Sender: emacs-devel-bounces+ged-emacs-devel=m.gmane.org@gnu.org Xref: news.gmane.org gmane.emacs.devel:190552 Archived-At: Hello, Eli. On Thu, Oct 01, 2015 at 11:48:40AM +0300, Eli Zaretskii wrote: > > Date: Wed, 30 Sep 2015 20:45:13 +0000 > > From: Alan Mackenzie > > In the Elisp manual, page "Window Start and End", it's described how, if > > in (set-window-start x) x is a position not at the start of a line, the > > display engine will, instead of x, choose some value near x as the > > window start. Is this really necessary? > The reason for this is that we want the physical beginning of the line > (i.e. the character after a newline or at bob) always be aligned at > the left edge of the window's text area, even if it is currently out > of view. This prevents annoying horizontal scrolling of long lines > when the beginning of the line comes into view. OK. But we're really talking here about where continuation lines start, not physical BOLs. > > The particular problem I'm looking at is with Follow Mode, where a pair > > of adjacent windows are of unequal width. This is a very common > > scenario - I frequently use Follow Mode with three side by side windows > > of widths 79, 79, and 80 (as measured by window-body-width). > > The problem occurs when there's a long line at the bottom of window 2 > > and its continuation line at the top of window 3. The display manager > > chops off the line in W2 after 78 characters, and inserts a \ sign. It > > then starts the continuation line in W3 at character 80 (counting from > > 1), assuming as it does, that the previous line in this window would be > > 79 characters long. So character 79 appears neither on the first > > portion of the line in W2, nor in its continuation in W3. This is > > suboptimal. > > This problem would not occur if there were a flag to set-window-start > > meaning "this value really is where I want the window to start, not some > > beginning of line nearby". > > How difficult would it be to relax the constraint on window start > > positions and implement this flag? > It's not difficult, at least in principle: the recalculation of the > window-start point is done in a single function. Not sure if it will > have adverse effects, though. You will surely have that horizontal > scrolling, but I don't know what other effects will be caused. I think scrolling such a window one screen line down would cause the break in the line to have to be repositioned. So it wouldn't be trivial. > But let me turn the table and ask you: how difficult would it be to > make sure follow-mode never lets a window end in the middle of a > continued line? In the worst case, very difficult. Indeed, with three follow windows, all of slightly different widths, and a fiendish specially constructed file, it could be that when you scroll the buffer a single screen line to deal with a break between W1 and W2, you create the same problem between W2 and W3. In such a scenario, you might end up scrolling the buffer quite a long way in the search for no "broken" continued lines at either boundary. With such a file there might be NO position where there isn't a break. In real life? I imagine it's quite common to use Follow Mode with very narrow windows (say, four at ~60 wide) when the annoyance of continued lines is less important than seeing all of a long function on the screen at once. There will then be lots of continued lines, and 3 window boundaries, W1-W2, W2-W3, W3-W4. If we were to go this route (of repositioning to avoid line breaks between follow windows), there would have to be a limit on how far one could scroll, with a value such as 3. This might have to be a customisation variable. -- Alan Mackenzie (Nuremberg, Germany).