10 Aug
2009
10 Aug
'09
4:14 p.m.
Hello Community,
I have committed today the first implementation of a new XWiki feature:
rendering mathematical equations into images. It is available as a
standalone component, and as a syntax 2.0 macro.
About the functionality.
Equations are written in the TeX/LaTeX syntax, which is pretty simple,
and seems to be the syntax of choice for mathematical equations in other
wikis, too. The macro can distinguish between inline and block equations
and render them accordingly. The output can be either PNG (the default
one), GIF or JPEG. While PNG is definitely the best, I kept the other
two in case somebody really wants to use ancient browsers that only
understand GIF.
Q: Should I leave just PNG as the output format?
Another feature is that the font size can be specified, in order to
render larger or smaller equations. All the font size commands from
LaTeX (from \tiny to \Huge) have an equivalent. I renamed them to a more
easy to understand name (also because the configuration is case
insensitive, so there's no difference between large and LARGE).
By default images are generated so that the font looks relatively OK
with the default XWiki skin on a 72 or 96 DPI display. They might look
disproportionate with a different DPI, or with a different default font
size.
Q: Is the default DPI setting OK?
Second, a few technical details:
The standalone component is located in
platform/core/xwiki-equation-rendering. I don't know if the name is the
best (Vincent complained). On one hand, this describes better what the
component does: it renders equations. On the other hand, it might cause
confusion with the xwiki-rendering system.
The component currently has three implementations:
- a native one, which relies on the latex system being present. It gives
the best results, from a graphical point of view, but requires the
presence of external programs, and involves a slight overhead for
starting new processes and for working with the disk. Currently it might
have some security problems, I'll have to see if opening input and
output files from TeX is a problem, or how to disable this. Any help
from someone who know more about TeX?
Q: Does anybody know of any security issues with running latex, dvips or
convert? Especially with the \openin and \openout commands?
- one which uses MathTran as a remote service through HTTP requests. It
gives results as good as the native one, enhanced with some metadata,
and depending on the configuration of the server, it might have better
performance than the native one. The disadvantage is that it relies
heavily on a remote server. Note that MathTran is free software, and can
be installed locally on the same or a neighboring server. Oh, another
minor problem is that it uses a variant of the TeX syntax, not LaTeX.
- one which uses SnuggleTeX and JEuclid to transform LaTeX into MathML,
and then render it into images. The results are not as eye-pleasing as
those obtained from LaTeX, but it is a self-contained solution, with no
external dependencies.
SnuggleTeX uses the liberal 3-clause BSD license, JEuclid uses the
Apache v2 license, so both can be deployed. Together, they weight in at
730k, so it's not a big impact. The other two implementations are not
contaminated by the licenses of the underlying system, so there's no
license conflict.
Q: Should either one be removed?
Q: Do you know of any other (better) alternative?
By default the native renderer is used, since it gives the best results
and doesn't depend on an external service. SnuggleTeX is configured as a
backup (safe) renderer which kicks in when the default one isn't working
(missing tex subsystem, or communication error with the remote server).
Q: Is this setup OK as the default one? (native by default, snuggletex
as fallback).
The generated images are stored in a cache (using the cache component),
for improved performance. This new cache might increase the memory
requirements, but fortunately it is easy to configure.
The rendering macro is located in
platform/core/xwiki-rendering/xwiki-renderig-macros/xwiki-rendering-macro-equation,
and the macro can be used with
{{equation}}\sum_{i=0}^{\infty}{{/equation}}.
Q: Is the macro name appropriate? Do you know of a better one?
Future work:
- make sure that there are no security issues with the Native backend
- add support for MathML display for the clients that understand it
- improve the alignment of images (especially for the Native backend),
as right now they are a bit raised above the text baseline
Many thanks to Guillaume Legris who provided the starting point for this
component.
--
Sergiu Dumitriu
http://purl.org/net/sergiu/