nsdejavu - Online in the Cloud

PROGRAM:

NAME

nsdejavu - DjVu browser plugin

SYNOPSIS

/usr/lib/x86_64-linux-gnu/mozilla/plugins/nsdejavu.so

DESCRIPTION

The shared library nsdejavu.so uses the Netscape browser plugin API to display DjVu images
in in a number of popular web browsers. Different web browsers provide various level of
support for Netscape plugins. Please check section "Browser Compatibility" for
instructions on how to enable the DjVu browser plugin.

The DjVuLibre browser plugin works by invoking a standalone viewer 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 intepreter 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 <[email protected]> and was then
improved by Bill Riemers <[email protected]> and Léon Bottou
<[email protected]>.

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