About Image Decoding with Pixmaps
This document describes extensions to the Plexus server to support arbitrary hypertext documents
from a mouse click on a picture.
Functionality discussed here isn't of much use unless you have
XMosaic version > 1.1
The Brief Idea
The basic idea is to have an X11 pixmap where each spot on the pixmap is
a specified color. This color corresponds to some document within
the scope of the current HTTP server.
There are several benefits:
- Arbitrary shape matching
- Easy expandibility (use your favorite pixmap editor (vi, xpaint, pixmap, etc...)
- Server independent. Users can add their own maps without adding
to the official server.
- Intuitive. (Well, I think so. Feel free to argue)
The Longer Description
- The user clicks on a picture. The picture is written in HTML as
<A HREF="something.html"><IMG SRC="a_map.gif" ismap></A>
- The
ismap
is what tells xmosaic to send back a URL
in the form previous_path/something.html?xplace,yplace
, where
xplace
and yplace
are the corresponding pixels
on the picture.
- The
HREF
in this case ends in .html
to
let xmosaic know to expect a HTML compliant doc. It could be .au
or .gif
depending on the author's desire
- The server sees that this is a query. It can't tell the difference
between an x,y click or a user query, so more definate criteria needs to
be met.
- The base file is
something.html
. This server checks
for the existence of something.html_ismap.xpm
If that
pixmap exists, then...
- The server parses the pixmap. Pixmaps have a field in their
color specs which allow for a comment. This comment can be
- relative to the current file, or
- absolute (with respect to
$http_root
) if it begins
with a slash.
- The extension of that file (the one retrieved from the comment)
is based on the extension of the base file name. The pixmap does not
specify .gif, .au, or .html, the server will add that extension. This
is to allow the same pixmap to server several types of media. (When
xmosaic supports it -- only HTML files can be recognized with xmosiac
<= 1.2)
More info / Disclaimer
- Xmosaic treats the result as text, whether it is a gif, au, or html.
- Of course this is a http server, so no other URL's can be specified.
Please contact me (or leave an annotation) with requests/ suggestions/
flames/ comments/ etc.
johnsonb@stolaf.edu
1. X PixMap format. Arnould Le Hors, lehors@sophia.inria.fr