NPAPI插件开发指南

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"NPAPI (Netscape Plugin Application Programming Interface) 是一种插件接口，用于在浏览器中嵌入第三方软件来扩展其功能。这份文档是NPAPI开发手册的英文版，包含了详细的API参考，适用于Netscape和Gecko浏览器。手册介绍了如何开发和使用NPAPI插件，涵盖了从基础概念到高级特性的全面内容。" NPAPI 插件是一种特殊的软件组件，允许开发者创建能在多种浏览器上运行的增强功能，比如播放视频、实现交互式内容或者处理特定文件类型。npruntime 是 NPAPI 的一部分，提供了与JavaScript交互的能力，使得插件可以在浏览器环境中执行复杂的逻辑。手册首先讲解了插件的基本原理，说明了插件是如何被浏览器调用和使用的。浏览器通常会根据MIME类型来检测和加载相应的插件，以处理不能直接渲染的内容。插件可以是窗口式的，有自己的绘制区域，也可以是无窗口式的，直接在网页内容中嵌入。插件的结构和API是手册的重点部分，它解释了如何利用NPAPI进行平台无关的编程，确保插件能在不同操作系统上运行。插件的窗口模式和无窗口模式各有特点，窗口式插件拥有独立的窗口，而无窗口插件则可以直接绘制在网页上。手册还详细阐述了如何通过HTML的`<OBJECT>`和`<EMBED>`标签来显示和控制插件。`<OBJECT>`标签提供更灵活的参数设置，而`<EMBED>`标签则更简单，通常用于基本的插件集成。此外，手册还讨论了嵌套规则和属性使用，确保正确地在HTML文档中嵌入插件。注册插件是开发过程中的重要步骤，手册列出了在Mac OS、MS Windows和Unix系统上的注册方法。插件实例的绘制、内存管理以及流的发送和接收都是插件开发者必须掌握的技术。同时，插件还需要能够处理URL，获取版本和用户界面信息，以适应不同的使用场景。这份NPAPI插件开发手册是开发和调试浏览器插件的宝贵资源，涵盖了从基础到高级的全方位指南，对于想要深入理解或开发浏览器插件的开发者来说具有很高的参考价值。

6 Gecko Plug-in API Reference

Plug-in Detection

Netscape Gecko looks for plug-ins in various places and in a particular order. The

next section, “How Netscape Gecko Finds Plug-ins,” describes these rules, and the

following section, “Checking Plug-ins by MIME Type,” describes how you can use

JavaScript to locate plug-ins yourself and establish which ones are to be registered for

which MIME types.

How Netscape Gecko Finds Plug-ins

When a Netscape Gecko-based browser starts up on Windows or Unix systems, it

checks for plug-in modules in the path pointed to by MOZ_PLUGIN_PATH.Afterthat,

it checks in the plug-ins directory for the platform:

• MS Windows:

plugins subdirectory, in the same directory as the browser appli-

cation.

•MacOS:

Plug-ins folder. A Mac OS plug-in can reside in a different directory

if you install a Macintosh alias that links to the plug-in in the Plug-ins folder.

•Unix:

usr/local/lib/netscape/plugins or $HOME/.mozilla/plugins.

If you want to use a different directory, set the

MOZ_PLUGIN_PATH environment

variable to its filepath, for example,

$HOME/yourplugins:/usr/local/lib/netscape/plugins.

Netscape Gecko searches any directory that this variable specifies. The local user

location, if it exists, overrides the network location.

• Finally, on the Mac, the browser scans the

~/Library/Internet Plugins

then /Library/Internet Plugins. Within these directories, the plug-ins are

orderedbydate.

On all platforms, the

plug-ins subdirectory or folder must be in the same directory

as the browser application. Users can install plug-ins in this directory manually, by

using a binary installer program, or by using the XPInstall API to write an installation

script, which the browser then uses to perform the installation. For more information

about these options, see Installing Plug-ins.

To find out which plug-ins are currently installed, choose About Plug-ins from the

Help menu (MS Windows and Unix) or "?" (Help) menu (Mac OS). Netscape Gecko

displays a page listing all installed plug-ins and the MIME types they handle, as well

as optional descriptive information supplied by the plug-in.

On Windows, installed plug-ins are automatically configured to handle the MIME

types that they support. If multiple plug-ins handle the same MIME type, the first

plug-in registered handles the MIME type. For information about the way MIME

types are assigned, see Registering Plug-ins.

8 Gecko Plug-in API Reference

Understanding the Plug-in API

A plug-in is a native code library whose source conforms to standard C syntax. The

Plug-in Application Programming Interface (API) is made up of two groups of

functions and a set of shared data structures.

• Plug-in methods are functions that you implement in the plug-in; Netscape

Gecko calls these functions. The names of all the plug-in functions in the API

begin with

NPP_, for example, NPP_New. There are also a couple of functions

(i.e.,

NP_Initialize and NP_Shutdown), that are direct library entry points

and not related to any particular plug-in instance.

• Browser methods are functions implemented by Netscape Gecko; the plug-in

calls these functions. The names of all the browser functions in the API begin

with

NPN_, for example, NPN_Write.

• Data structures are plug-in-specific types defined for use in the Plug-in API. The

names of structures begin with

NP, for example, NPWindow.

All plug-in names in the API start with

NP. In general, the operation of all API

functions is the same on all platforms. Where this varies, the reference entry for the

function in the reference section describes the difference.

Plug-ins and Platform Independence

A plug-in is a dynamic code module that is native to the specific platform on which

the browser is running. It is a code library, rather than an application or an applet, and

runs only from the browser. Although plug-ins are platform-specific, the Plug-in API

is designed to provide the maximum degree of flexibility and to be functionally

consistent across all platforms. This guide notes platform-specific differences in

coding for the MS Windows, Mac OS, and Unix platforms.

You can use the Plug-in API to write plug-ins that are media type driven and provide

high performance by taking advantage of native code. Plug-ins give you an

opportunity to seamlessly integrate platform-dependent code and enhance the

Netscape Gecko core functionality by providing support for new data types.

The plug-in file type depends on the platform:

• MS Windows: .DLL (Dynamic Link Library) files

• Unix: .SO or .DSO (Shared Objects) files

• Mac OS: PowerPC Shared Library files.

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