Tribblix: manual page: nsdejavu.1

NSDEJAVU(1) DjView-4 NSDEJAVU(1)

NAME

nsdejavu - DjVu browser plugin

SYNOPSIS

/usr/lib/amd64/mozilla/plugins/nsdejavu.so

WARNING

Using nsdejavu as a plugin in 2020 is very difficult because popular
browsers either do not support netscape plugins (chrome), or removed
support for netscape plugins other than flash (firefox). We regret
this decision because djview/nsdejavu is a perfect example of very
well behaved plugin that would have been easy to support.

DESCRIPTION

The shared library nsdejavu.so uses the Netscape browser plugin API
to display DjVu images in in a number of popular web browsers. It
works by invoking a standalone viewer out-of-process with the special
command line option -netscape. The plugin first searches a program
named djview. If this program cannot be found, it searches for
djview4 and finally djview3. It is always possible to override this
search strategy by setting the environment variable NPX_DJVIEW to the
full path of the desired executable.

MIME TYPES AND EXTENSIONS

Typing the URL of a recognized DjVu document in your web browser
should automatically invoke the DjVu browser plugin. Each browser
uses different methods to determine that a particular URL is in fact
a DjVu document. Web server normally provide a MIME type to web
browsers. The official MIME type for DjVu documents is
image/vnd.djvu. For compatibility with ancient versions of the DjVu
viewer, it is common to use instead the experimental MIME type
image/x-djvu or image/x.djvu. Web servers should be configured to
send the proper MIME type for DjVu documents. Most web browsers also
recognize files ending with .djvu or .djv as DjVu files.

An easy way to check if an http server is giving an appropriate
content-type is to invoke the following command with a URL
corresponding to an actual DjVu file on the server.

curl -u URL | grep Content-Type

The result should be one of the following, preferably the first.

Content-Type: image/vnd.djvu
Content-Type: image/x.djvu
Content-Type: image/x-djvu

Any other MIME type indicates a server misconfiguration.

CGI-STYLE FLAGS
The behavior of the DjVu browser plugin can be specified by
augmenting the URL using a syntax similar to that used by the CGI
programs. This syntax is described by the following template:

http://.../file.djvu?djvuopts&keyword=value&keyword=value&...

The DjVu browser plugin only recognizes keywords that appear after
the word djvuopts. The keywords recognized by each viewer are listed
in the corresponding man page. Unrecognized keywords are ignored.
The most common keywords are:

page=pagename
Specify which page is displayed by name or by ordinal number.

zoom=zoomfactor
Set the zoom factor. Legal values for zoomfactor are:

+-------------------------------------------------------+
|number Magnification factor in range 10% to 999%. |
|one2one Select the "one-to-one" mode. |
|width Select the "fit width" mode. |
|page Select the "fit page" mode. |
|stretch Stretch the image to the plugin window size. |
+-------------------------------------------------------+

BROWSER COMPATIBILITY

The DjVu browser plugin has been tested with several popular web
browsers: Netscape 4 and 6; Gecko based browsers such as Mozilla,
Galeon and Firefox; KHTML based browsers such as Konqueror; and
Opera. Please read the browser documentation to find out where the
plugin library should be installed.

EMBEDDING DJVU IMAGES IN HTML PAGES

You can integrate DjVu content on an HTML web page with either the
<embed> or the <object> tag. This method will work even if your web
server does not support the DjVu MIME type. The CGI style flags can
be directly used as attributes of the embedding tag. The following
example shows the W3C standard syntax with the OBJECT tag:

<object data="myfile.djvu" type="image/vnd.djvu"
width="100%" height="100%" >
<param name="page" value="iii">
<param name="zoom" value="stretch">
This browser cannot render djvu data.
</object>

And this is the customary syntax with the EMBED tag:

<embed src="myfile.djvu" type="image/vnd.djvu"
width="100%" height="100%"
page="iii" zoom="stretch"></embed>

INTERFACING THE DJVIEW PLUGIN WITH JAVASCRIPT

Recent versions of the djview4 plugin can be controlled from the
JavaScript interpreter of browsers implementing the Mozilla NPRuntime
API. To access the plugin object, include the attribute
id="pluginname" into the <object> or <embed> tag and use the
JavaScript function getElementById("pluginname").

The plugin object implements two methods to retrieve and set the
value of the options usually recognized as CGI-style flags. It also
can evaluate a specified JavaScript expression whenever something
changes in the status of the djview interface.

pluginobject.setdjvuopt("key",value)
Set the value of the djvu option key to the character string
value. This achieves the same effect as specifying option
key=value among the CGI-style flags. For instance, values of
the key page can be page IDs, page titles, page numbers, or
page names.

pluginobject.getdjvuopt("key")
Return the value of the djvu option key as a string. The
returned value is always a character string, even when the
return is logically a number. Boolean values are returned as
strings yes or no. Besides the usual CGI-style flags, this
function recognizes the additional key pages and returns the
total number of pages in the DjVu document. An empty string
is returned when the key is not recognized.

pluginobject.onchange="code";
Ensure that string code is evaluated in the context of the
plugin object whenever something changes in the djview
graphical user interface. For instance, this evaluation
happens when progressive refinements are painted, and when the
user manipulates the image interactively.

pluginobject.version
Return a string describing the plugin version. This property
can be used to test whether the djview plugin is scriptable in
this browser.

Note that the scriptability feature may not be accessible until the
djview plugin is fully loaded. Therefore it is advisable to check
pluginobject.version from the JavaScript onload before calling any
other method.

CREDITS

This program was written by Andrei Erofeev <andrew_erofeev@yahoo.com>
and was then improved by Bill Riemers <docbill@sourceforge.net> and
L'eon Bottou <leonb@users.sourceforge.net>.