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My new opensource project: Flying Saucer, an all Java XHTML renderer.

Posted by joshy on June 18, 2004 at 1:05 PM PDT

I normally try to be even handed, un-biased, and bi-partisan; but today
I'm going to shamelessly use my muchly vaunted position as a highly skilled
blogologist in field of to plug my new project: Flying Saucer, an
all Java XHTML + CSS renderer.

When I was doing research for my two part series on HTML renderers for
Swing (pts href="">1 &
I got to thinking Why are there so few renderers, and almost none that
are opensource? Is it really that hard?
. Initially I tried to fix some
of the bugs in the HTMLEditorKit that comes with Swing, but found a slew of
private methods that prevented me from improving it through subclassing. I
also tried editing the Swing code itself during a four hour cross country
flight, but to no avail. And even if I had made the changes I couldn't have
released them with the current Swing license. With so little to go on I
struck out on my own. I mean, really, how hard could it be? :)

Two months of hacking an hour here and there I found out how hard. It was both
easier and harder than I expected.
. To make life easier on me I decided
to leave out everything that didn't directly have to do with rendering HTML on
the screen. I dropped the idea of making a complete browser with a UI,
javascript, debugging, bookmarks, history, etc. Those are all important but
not the hard part. Since CSS and XML parsing are already provided by other
libraries I reused them instead of reinventing the wheel. It's not that I
dislike wheel inventing, it just that I have to be realistic about what
one programmer can do in his spare time.

With that out of the way it was still too big. The core renderer of
Mozilla took years to develop and the full time work of several top notch
programmers. Gotta cut it down. Thinking about it, though, I don't need a
complete webbrowser like IE or Mozilla. Since this is for embedding in my
own programs most of the content will be generated by my own code. I don't
need to deal with every browser bug and every malformed webpage out there.
I could get by with strictly compliant pages and worry about quirks
handling in a compatibility library. (to be built later, of course. :)

Now, if I'm going to write a new renderer from scratch I should go for
the gold, ie: complete XHTML + CSS 2.0 (now 2.1). It's actually not as hard
as I thought. The W3C makes some completely exhaustive
specifications. The CSS 2 spec in
particular is huge, but it does describe in great and explicit
how each feature should behave (giving Internet Explorer no
excuse for it's bugs).

So what do we have. I've written a renderer that takes a
org.w3c.dom.Document object with inline styles and renders it into a
scrollable JPanel. Most of plain HTML is supported, as are the full box
model, tables, and images. Parts of relative, absolute, and fixed
positioning work. The main issue is the bugs in float/clear, and the lack
of forms support. Oh yeah, and it's really, really, really slow (Need some
help with that. I used regexs for the text parsing). But it works and the
supported features are pretty compliant.

I was actually surprised at how much I've done by myself. Still, I know
the limits of one programmer, which is why I'm launching it as an
open source project right here on And I need your help!

This is a challenging project that needs some top-notch people. If you
feel you are up to it then sign on to the project and join the dev
mailing list. In particular I want to start breaking it up into modules and
find owners for each:

  • Rendering compliance (research the latest standards, build it, test it)
  • CSS (parsing, converting, optimizing, rendering new features)
  • HTML->XHTML converter (support for HTML 3/4.0 pages)
  • Browser component (a standalone webbrowser based on Flying Saucer)
  • Javascript support (how do we plug in rhino?)
  • I18N efforts (how do we make sure the whole thing is i18n-able)
  • forms (input, select, text area, etc)
  • object and plugin support (SVG, xforms, flash, pdf)
  • printing module (we can't print anything yet!)
  • network module (ssl, redirects, image loading, etc.)
  • performance and memory optimization (how do we make the whole thing as fast and light as possible)

I really think that a complete XHTML renderer is a vital component of
any modern programming toolkit, and I'd like to see Flying Saucer become
the best of breed implementation for Java. It's a lot of work but it's
going to be rewarding. Come on in. The water's fine!

Oh, to just play with it quickly check the source out of cvs or download href="">this
zipfile. You only need Ant and the 1.4 JDK. Run ant
to launch the test program. Select different tests from the
Test menu.

Update: I forgot some links. the project is here and the mailing list is here.

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