patches for Smooth scrolling (in rxvt)

how to keep reading while scrolling

This page contains patches to make scrolling inside rxvt comparable with smooth-scrolling in firefox. WARNING: it is not very usable with LCD screens. Read why in this excellent article by Dave Marsh, about eyes & monitors.

Table of Contents

• why did i set to implement it
• bugs to consider before
• story how it got implemented
• download the patches
• plans for emacs ?
• demo: a demo for Sawfish users, no need to (re-)compile!

News!

• I have a patch for less to use smooth-scroll feature of my rxvt. (that means also man(1)).
• rxvt's own scrolling (by Shift-Up/Down) uses it too!
• GKT+ is working on it too:

Why?

I find it useful to use text-only elinks web browser instead of firefox. (I use it for html documentations, and wsws, where I usually don't expect images).

But web pages are more than 1 page, and i need to scroll. Firefox has a nice smooth scrolling (now smooth-wheel) , and I think, that given a good keyboard control, with smooth scrolling it is possible to read while scrolling. Text scrolling by line-height skips is disturbing; while ending titles in films are readable!

Bugs:

• If the rxvt window is not fully visible (partially obscured), wrong pixels will scroll. Particular case is described here. Hard to solve for now, I should reimplement a system from gtk+ which solves it.
• Inside elinks it does not work with html frames, when you scroll only one of them :(
• auto-repeat is possibly too fast to just keep scrolling keys down.

History

I knew the "difference" algorithm (pdf), but this needed a different one: heckel algorithm. I couldn't find free documentation, so I took some free implementation and read it till I understood, that "heckel" algo is about heuristics, it does not solve e well defined problem. It is used in ncurses,

I want this algo to find out a "scroll similarity" between 2 sequences of text.

But first a bit of background:

• Elinks often redraws screen by pushing full page redrawing sequence (program).
• such program starts with clear-screen instruction.
• in October 2005, I was solving problems around flickering. I disliked the flicker due to that clear-screen instruction. I wanted rxvt to keep a snapshot of the screen, and render only the "final" image. The finality had to be signalled by elinks, by the second Esc. sequence. I call them freeze and unfreeze "rxvt commands": escape sequences.
• But, at the moment of unfreeze I was able to test for scrolling & do the smooth scroll!

Formulation of the problem:

• First I had to detect which part of screen was scrolling, and what was the shift (in text line units).
• by using XCopyArea do a series of micro-scrolls.

solution:

Historical curiosity:

When I feed the Xserver with the sequence of XCopyArea calls, it is not fast as I would have wished for.... by which I mean I didn't have to interleave them with some pauses. The speed is just fine on my matrox G450 @ 1920x1440 (bandwidth 2.7GB/sec) & amd 1700 xp. That's just a lucky combinationn in my case.

• After using (for a month) a version which tested for shift by -2 (text scrolling up in elinks), I implanted (in rxvt) my simplified version of heckel algo, and obtain the shift/scroll number, and 3 regions: top & bottom group of lines which don't scroll, and the rest which scrolls (there is a minimum percentage of lines which need to do the same movement, below which I don't use the scrolling).

Response

as is the tradition on #rxvt-unicode I didn't get any positive feedback: see irc log

patches

(you can get gentoo ebuilds here: rxvt and elinks)

• patch for rxvt-2.7.10 Sorry it is a patch against an already patched tree (some patches from gentoo), you can tak my complete tarball.

How to build:

# Possibly add      --prefix=/usr  ?

./configure --enable-everything --enable-rxvt-scroll --enable-next-scroll --enable-xterm-scroll
--enable-transparency --enable-xpm-background --enable-utmp --enable-wtmp --enable-mousewheel
--enable-slipwheeling --enable-smart-resize --enable-256-color --enable-menubar --enable-xim
--enable-shared --enable-keepscrolling --with-term="rxvt"

make
make install          (as root)

• very small patch for elinks 0.11.1

  How to build:

  cd elinks-0.11.1
  patch -p1 < flicker-rxvt.patch 
  ./autogen.sh     (dunno why I get compilation errors without this, on gentoo, with gcc 4.1)
  ./configure   --prefix=/usr --sysconfdir=/etc/elinks --enable-leds --enable-256-colors
  

• patch for less-394l (there is a problem with the less 'F' command though)

FAQ:

• keyboard Auto-repeat is faster than the rendering, so after a while the page makes a skip.
  

Fine-scrolling is invoked only when the scroll step is less than 10 lines (up- or down-wards). I suggest setting they key-repeat low enough, so that you can just keep the key down and see the page flow. I use

xset r rate 190 10 

• tuning:

  rxvt -scrollstep 3 -scrollpause 10000
  

  ... microsteps shift by 3 pixels, and are interlaced by 10 millisecond pauses.

Todo:

Demo for Sawfish users:

I changed a bit the slide-window function to use microsteps.

http://maruska.dyndns.org/comp/activity/sawfish/wm/commands/slide-window.jl

but there has been a similar code in another sawfish extension! http://djdeath91.dyndns.org/~djdeath/animate-move.jl

Page started 8/1/2006