From mboxrd@z Thu Jan 1 00:00:00 1970 Path: news.gmane.io!.POSTED.blaine.gmane.org!not-for-mail From: Eli Zaretskii Newsgroups: gmane.emacs.help Subject: Re: Set-window-vscroll sometimes doesn't work Date: Sun, 18 Oct 2020 20:31:21 +0300 Message-ID: <83imb7qw46.fsf@gnu.org> References: <72B62847-3F35-412A-9F74-88442A936B19@gmail.com> <83eelvsivm.fsf@gnu.org> <853C8CD1-B58B-4F22-A889-4AB2AEE3DD80@gmail.com> Mime-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: 8bit Injection-Info: ciao.gmane.io; posting-host="blaine.gmane.org:116.202.254.214"; logging-data="14887"; mail-complaints-to="usenet@ciao.gmane.io" To: help-gnu-emacs@gnu.org Original-X-From: help-gnu-emacs-bounces+geh-help-gnu-emacs=m.gmane-mx.org@gnu.org Sun Oct 18 19:31:47 2020 Return-path: Envelope-to: geh-help-gnu-emacs@m.gmane-mx.org Original-Received: from lists.gnu.org ([209.51.188.17]) by ciao.gmane.io with esmtps (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.92) (envelope-from ) id 1kUCX3-0003k8-Jr for geh-help-gnu-emacs@m.gmane-mx.org; Sun, 18 Oct 2020 19:31:45 +0200 Original-Received: from localhost ([::1]:58476 helo=lists1p.gnu.org) by lists.gnu.org with esmtp (Exim 4.90_1) (envelope-from ) id 1kUCX2-0000al-Lw for geh-help-gnu-emacs@m.gmane-mx.org; Sun, 18 Oct 2020 13:31:44 -0400 Original-Received: from eggs.gnu.org ([2001:470:142:3::10]:39766) by lists.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.90_1) (envelope-from ) id 1kUCWd-0000aO-58 for help-gnu-emacs@gnu.org; Sun, 18 Oct 2020 13:31:19 -0400 Original-Received: from fencepost.gnu.org ([2001:470:142:3::e]:46942) by eggs.gnu.org with esmtp (Exim 4.90_1) (envelope-from ) id 1kUCWc-0006O6-Ru for help-gnu-emacs@gnu.org; Sun, 18 Oct 2020 13:31:18 -0400 Original-Received: from [176.228.60.248] (port=3153 helo=home-c4e4a596f7) by fencepost.gnu.org with esmtpsa (TLS1.2:RSA_AES_256_CBC_SHA1:256) (Exim 4.82) (envelope-from ) id 1kUCWb-00015o-JT for help-gnu-emacs@gnu.org; Sun, 18 Oct 2020 13:31:18 -0400 In-Reply-To: <853C8CD1-B58B-4F22-A889-4AB2AEE3DD80@gmail.com> (message from Yuan Fu on Sun, 18 Oct 2020 13:24:25 -0400) X-BeenThere: help-gnu-emacs@gnu.org X-Mailman-Version: 2.1.23 Precedence: list List-Id: Users list for the GNU Emacs text editor List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Errors-To: help-gnu-emacs-bounces+geh-help-gnu-emacs=m.gmane-mx.org@gnu.org Original-Sender: "help-gnu-emacs" Xref: news.gmane.io gmane.emacs.help:124545 Archived-At: > From: Yuan Fu > Date: Sun, 18 Oct 2020 13:24:25 -0400 > Cc: help-gnu-emacs@gnu.org > > No. The problem is in your code. First, you use set-window-start and > scroll-down, both of which tramp window-vscroll (as you probably > realize if you think about what those do). > > Why is so? Is there any material that I can read about these? These two functions force Emacs to display the buffer starting at a particular position, so vscroll is zeroed out. Otherwise, how could Emacs obey the forced start point? > This works, but brings flickers: the image first shows completely then the vscroll takes effect, which is > reasonable but not preferred. It was just an example to explain to you what should be done. E.g., when you scroll a tall image with C-n there's no flickering. You just cannot mix vscroll with other code that affects the window display, that's all. > I found that using (set-window-start nil (point) t) with the third argument non-nil > gives me the desired effect. My guess is that, as the doctoring said, setting that to non-nil prevents redisplay > to try to make point completely visible, so redisplay doesn’t modify vscroll, so my vscroll value survived. Is > that right? NOFORCE non-nil means Emacs doesn't have to display the window starting at the position if there are valid reasons, so yes. But my suggestion is not to use set-window-start when you want to vscroll, it's unsafe. You in effect create a conflict for the display engine, and have no control on how it will resolve that conflict.