[OS X TeX] Flash mode prototype for Alpha (with xdvi)

Sun Jan 9 17:09:49 EST 2005

Hello flashers,

Here is a different approach to flash mode, for AlphaX and xdvi.  
It is a relatively short Tcl script and it runs inside AlphaX.  

It works by notification instead of by polling.  Instead of having the
various components check every fraction of a second if there is anything to
do, the components here communicate via a two-way pipe and via event hooks,
notifying each other when an action is required.  This means there is no
unnecessary waiting time -- the updating occurs as soon as possible.  (It
also means that when idle (nothing is typed in the tex source window), the
workload is zero.)  In my primitive timing experiments (on my iBook 500MHz
G3), this flash mode is about 3 times faster than Claus Gerhardt's
AppleScript flash mode!

(I think it will not be difficult for an emacs scripter to implement this
approach in emacs -- I doubt it will be possible in AppleScript...)

Main shortcoming: currently it works only for single-file tex jobs.

The script can be found at

http://mat.uab.es/~kock/alpha-tcl/flash.tcl.gz

I am eager to hear if it works for others, and how it feels on faster machines.
Below is some more blurb from the header.

Cheers,
Joachim.

# -*-tcl-*-   nowrap   encoding="utf-8"
# 
# File:    flash.tcl
# Version: 2005-01-09 22:50
# Author:  Joachim Kock <kock at mat.uab.es>
# License: This is open-source, BSD style licence.
# 
# Thanks to Claus Gerhardt for his pioneering work on flashmodes,
# motivating the present contribution.
# 
# 
# 
# Flash mode prototype for Alpha (with xdvi)
# ==========================================
# 
# 
# Overview
# --------
# Flash mode is the feature peculiar to Textures, by which a preview window
# continuously reflects the changes in the source document.  Recently Claus
# Gerhardt has implemented a version of this as a compiled AppleScript
# application controlling an editor and a previewer.
# 
# The present Alpha 'plugin' is a short Tcl script to achieve a flash
# effect between Alpha and xdvi.
# 
# It's approach is different from Claus Gerhardt's in two main respects:
# 
# 1) it doesn't modify the source file itself, and uses instead a temporary
# file, together with a dynamically precompiled custom tex format.
# 
# 2) it works by notification instead of by polling.  Instead of having the
# various components check every fraction of a second if there is anything
# to do, the components here communicate via a two-way pipe and via event
# hooks, notifying each other when an action is required.  This means there
# is no unnecessary waiting time -- the updating occurs as soon as
# possible.  (It also means that when idle (nothing is typed in the tex
# source window), the workload is zero.)
# 
# 
# Speed and usability
# -------------------
# I am testing this on my good-old 500MHz G3 iBook (without Quartz
# Extreme).  The mechanism typesets a 2-page document about 90 times per
# minute (which I think is comparable to what Textures achieves on
# documents of this length (?)), hence the maximum amount of time elapsing
# from a character is typed until it appears in the preview window is about
# 0.66 seconds.  However when the document is in an unstable state
# (unmatched dollar sign or such), the gap can be somewhat longer.  For
# long documents, there is an option to preview and flash only the
# surroundings of the cursor, i.e. only current paragraph.  This works at
# about the same speed, independently of the size of the document.  xdvi is
# a bit flashy when refreshing the preview window's content.  Hopefully
# this will not be a problem on newer computers with faster processors and
# Quartz Extreme.
# 
# 
# Shortcomings
# ------------ 
# This is only a prototype.  To keep the flash script as simple as possible
# in this phase of development (and because of general laziness), I have
# refrained from several obvious refinements.  The current shortcomings
# include:
# 
# No effort has been made to make this work for multi-file tex jobs.
# Getting this to work will not be too difficult -- most of the needed
# functionality is already available in AlphaTcl.
# 
# There is a fair chance things will break down if there are many users
# logged in using x-windows at the same time.
# 
# The window geometries are currently hardcoded to fit on a 1024x768 
# display -- squeezed!  It would not be too difficult to automatically
# adjust to the screen size, or provide these settings as preference flags
# where the user can write his own idiosynchrasies.
# 
# Because the dvi is produced from a temporary file, right now standard
# synchronisation doesn't work optimally together with flash mode: all
# line indications are shifted by the number of lines in the preamble!
# Fixing this will require a few tweaks to Alpha's synchronisation code,
# but there is no technically difficulty in this project.
# 
# It would be nice to support also pdftex, and other previewers.  In
# principle there should be no difference, but I had some trouble with
# custom formats in pdftex...
# 
# The partial flash mode is certainly not very well polished, and fails
# if you are typing near the top of the document!  It is just a very quick
# hack...
# 
# I don't think it works in AlphaTk, since I have been a bit sloppy with
# file positions...
# 
# 
# Instructions for installation and usage
# ---------------------------------------
# Place this file /anyhwere/you/want and write the following line in
# your prefs.tcl file:
# 
#     source /anywhere/you/want/flash.tcl
# 
# Then restart Alpha.
# 
# To try out the mechanism, first make sure Xwindows is running.  Open a
# tex document (a self-contained latex document) and press F2.  Then start
# typing.  To stop the mechanism, press shift-F2.  (The mechanism also
# stops automatically when the source window is closed.)  (If these
# keyboard shortcuts are in conflict with others, you can change them using
# Alpha's usual syntax for key bindings, e.g.
# 
#     Bind 'a' <scoz> TeX::flash::startFlash TeX
#     
# to use Shift-cmd-opt-ctrl-A.)
# 
# You can save the document when you want, it has no direct influence on
# the flash behaviour, except that changes to the preamble only take effect
# when the document is saved.
# 
# To try out the partial flash mode (typesetting only current paragraph),
# you have to write the following command in the AlphaTcl shell (Cmd-Y):
# 
#    set TeX::flash::partialFlash 1
#    
# If you want this as a permanent setting, write it in your alpha.tcl file.
# 
# 
# Technical remarks
# -----------------
# A flash cycle consist in the following actions: write the temp file, tex
# the temp file, move the dvi file to replace the original, refresh xdvi.
# The flash mechanism is busy when any of these actions takes place,
# otherwise it is IDLE.  The flash mechanism can be triggered by two sort
# of events:
# 
# -- when a character is typed in the source window (and if the mechanism
# is IDLE).  This is detected by the characterInsertedHook [detectTyping].
# 
# -- when the cycle terminates (and if the window is DIRTY).  This is
# detected by the pipe-readable eventhandler [detectSignal].  The window
# is considered DIRTY if a character has been typed after the flash cycle
# has been initiated.
# 
# The flash cycle is initiated by [writeTempFileAndContinue], who then
# sets IDLE = 1 and DIRTY = 0.  Setting these variables in the other 
# direction is done by the two triggers just mentioned.
# 
# A custom tex format file is maintained, corresponding to the content of
# the preamble of the source file.  Whenever flash mode is turned on and
# also whenever the source file is saved, there is a saveHook that checks
# if the preamble has changed (comparing a checksum with one recorded when
# the format was built).  In that case the format file is rebuilt.
# 
# Note: the hooks are written for old-style pre-8.0 AlphaTcl.  They can 
# be simplified in AlphaTcl 8.1.

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