it's so easy

Sometimes, I like to use mathematical notation in webpages, either to impress people or simply for decoration. One way to do that is MathML, which is an XML-based markup language for mathematical notation. However, many browsers do not support MathML at all, or require you to download plugins and/or special fonts. Another problem with MathML is that XML is a really inconvenient format to edit by hand. Practically, you'll need some kind of formula editor.

tex vs mathml

As an old-schooler, I prefer to use the math-notation invented for TeX instead - it is short and sweet and powerful. Donald Knuth invented the whole TeX language because he was unhappy with the quality of typesetting of mathematic, and it is widely used in both computer science and mathematics. Anyway, I'm sure many people remember the 'abc-formula' to calculate the roots of a quadratic function :

In the TeX-sublanguage for math, one can specify the formula as follows:

 -b \pm \sqrt{b^2 - 4ac} \over 2a

The corresponding MathML is no fewer than 20 lines; see the example in Wikipedia. Clearly, MathML is not designed for hand-editing. There are are some editors available, but hand-editing TeX is much faster (at least for me); and, as mentioned, even if you have the MathML, many browser will not show it correctly.

So what I'd like is a way to use (i) TeX-notation and (ii) have it display correctly in any (graphical) browser. One way to that is to use LaTeX to process and render the formulae, and convert that to a PNG-image. In 2004, I wrote a little tool called WebTeX to create small images from TeX-formulae. It was nothing too fancy; you enter a <img ...>-element with some decription of some formula, and the little tool would turn it into an image, using LaTeX and ImageMagick. I don't maintain that old tool anymore - it was time for something new. Therefore...

texdrive

This weekend, I wrote a new maths-in-webpages tool using emacs-lisp. The emacs-integration makes adding formulae to html-pages really easy. For example, if I want to include the famous Bayes' Theorem, I simply type:

  M-x texdrive-insert-formula
  Formula: $P(A|B) = \frac{P(B|A)P(A)}{P(B|A)P(A) + P(B|\overline{A})P(\overline{A})}$
  Title: bayes-theorem

Et voilà; the following is inserted:

  <img src="bayes-theorem.png" title="bayes-theorem"
        class="texdrive-formula" name="$P(A|B) = \frac{P(B|A)P(A)}{P(B|A)P(A) + P(B|\overline{A})P(\overline{A})}$"
        border="0">

Now, all we need to do is texdrive-generate-images-from-html, and the corresponding image will be generated:

So, for immediate download: texdrive.el. It works pretty well for me; please let me know if you have any problems or are missing something. In some cases, the formulae are not as sharp as they could be; I hope I'll be able to improve it with some tweaking. Anyway, it's nice to see how one can solve problems by glueing together some existing open-source tools. Standing on the shoulders of giants...

Note that some wiki-software, notably Wikipedia's MediaWiki, use a similar approach.

a kind of magic

Today just a short tip: if you are using emacs and git, I can recommend magit.

Magit is a git-mode for emacs, which makes using git convenient and easy to use. Magit was created by running mate Marius. It's under heavy development, but I have been a happy user for while. There is even a user manual, which you actually don't need very much, as things work very much as you would expect.

If you are not using emacs, this might be a good reason to start.

waiting for 22

Achilles had Patroclus. Don Quixote had Sancho Panza. Michael Jackson has Bubbles. And I have emacs. On my N810. A while ago, I already wrote about it. I even showed some screenshot of emacs running in scratchbox. But, I didn't take the final step - getting it to run on an actual N810. Recently, I tried to get that to work. Well, that was frustrating... Some hackish instructions follow. They may or may not work for you -- try at your own risk :)

• First I tried to simply rebuild the Emacs23-packages in scratchbox; that failed, because the compilation somehow crashes QEMU;
  
• Then I tried Emacs 22 instead... but the problem remained;
  
• So, I decided that maybe I should try to compile the package it on the N810 itself. Again, that failed. One of many problems: package building requires a real grep, and if you try to install it, it wants to remove the whole busybox environment; sigh. I fought the system - the system won...
  

But, all was not lost. There are prebuilt Debian packages of Emacs22 available; I took the armel-packages from there, and tried to install them. That almost worked. Almost, because the size of emacs is almost legendary. It did not fit on my root file system on the N810.

We're nearing the solution though; I copied the contents of the .debs to a directory emacs810 (with mc); then I copied this directory to the MMC-card of the N810 (/media/mmc2/). I set some symlinks, ie.

  # ln -s /media/mmc2/emacs810/usr/share/emacs /usr/share/emacs
  # ln -s /media/mmc2/emacs810/usr/share/emacs22 /usr/share/emacs22
  # ln -s /media/mmc2/emacs810/usr/bin/emacs22-gtk /usr/bin/emacs22
  # ln -s /media/mmc2/emacs810/usr/share/applications/emacs22.desktop /usr/share/applications/hildon/

Also, you'll need to install libungif4g. That should do the trick, and emacs should show up in your Extras-menu. And we can run emacs! Victory is mine!

Well, almost. In emacs, a very useful key is the Meta-key, usually mapped to the Alt-key of your keyboard. But of course, there's no alt-key on the N810-keyboard. Instead, I decided to remap the Chr-key. I'd like to remap it in my .emacs, but I haven't been able to do so.

Anyway, as a first start, I added these to /usr/share/X11/xkb/symbols/nokia_vndr/rx-44 (the xkb keyboard mapping):

   key <SPCE> {  [ space, space, Tab, space ] };
   key <COMP> {  [ Meta_L, Meta_L, Multi_key, Meta_L ] };
   
   modifier_map Mod1 { Meta_L };

The first one will turn Fn-Spc into Tab, which is very useful for completion (for some reason, I couldn't get M-i working in the minibuffer). The second one will turn the Chr key into the M-key (obviously, you can't run emacs without that), with Fn-Chr giving the old Chr key. Not sure what it will break - it's black magic.

Ok, that's it. These steps should be cleaned-up, pre-packaged and made single-click-available. Anyway, the steps above should hopefully get you a working hand held emacs. Happy hacking!

beyond the dark sun

Friday -- another week has flown by. Winter has not really entered Finland yet, there's just ultragray autumn weather, a lots rain, few hours of daylight, not even some Finnish wintersun... But thankfully, my moods are not very dependent on the weather, and I am happily hacking away still.

• Googler Steve Yegge is blogging about combining Javascript and Emacs. Naturally, I am interested in just about anything combined with emacs, but this sounds quite interesting; not only about fully supporting javascript in emacs, but actually being able to write extensions in javascript (instead of elisp). Apparently, he already implemented a full javascript interpreter in elisp. Very cool... but show us the code!
  
• I've been playing with Alberto Garcia's LastFM-client Vagalume; it works very nice on my N810 (versions for 770, N800 are available). last.fm is pretty cool anyways, but the vagalume makes it work very smoothly. Obviously, I am hdbngr there :-)
  
• We've been working on the downloadable packages for the modest email client, it's almost done, stay tuned.
  
• Said goodbye to my friend Andrea, who's going back to Italy. I'll miss him as a person and as a great host for Italian food... At least he will be in good hands there. Arrivederci!
  

NM156

It's unwise to discuss politics or religion with strangers -- or even worse, discuss favourite text editors... My personal favourite is GNU/Emacs. It took me some time to get familiar with this thermonuclear word processor, but after that I found it a wonderful tool. You can actually run Emacs on your N8x0 - see the screenshot of Emacs 23 from CVS. But that's not what I'd like to discuss here.

For maemo software development, many people seem to use a bunch of terminal windows inside and outside Scratchbox. Some alternatives exist, such as Laika, the Maemo-plugin for Eclipse, and work is apparently underway for Anjuta as well.

Anyway, I've been coding using Emacs for almost a decade, so obviously I'd like to integrate it with the Maemo/Scratchbox-environment as well - and yes, it is possible to do the following:

• Run Emacs outside Scratchbox;
  
• Compile inside Scratchbox;
  
• Jump to the right place in the source with one click from any compiler errors/warnings.
  

How to get that to work? It's embarrasingly easy (once I figured it out):

First, make sure the same source code can be reached using the same path both inside and outside Scratchbox, by using symlinks, for example:

$ ln -s /scratchbox/users/djcb/home/djcb/src/my-app /home/djcb/src/my-app

Having done that, it's easy to add some trivial Elisp to your .emacs:

;; compile inside scratchbox
(defun scratchbox-c-mode-compile ()
(interactive)
(compile (concat "scratchbox make -C "
               default-directory)))

That's all. You can now edit your source code in your normal Linux environment, open a file in ~/src/my-app/..., and compile it with M-x scratchbox-c-mode-compile. Or even better, use a keyboard macro (add to your .emacs):

(define-key c-mode-base-map (kbd "<f8>")  'scratchbox-c-mode-compile)

And pressing F8 is now enough to start compiling...

Now, what's a blog entry without some screenshot? Here's one, running Emacs 23 (from CVS) inside Scratchbox - unrelated to what discussed above, but a nice picture anyway :)

Obligatory dot-emacs link. Happy hacking!