p.r bharat raj and jinu mathew abstract:

8/14/2019 p.r Bharat Raj and Jinu Mathew Abstract:

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GECKO

P.R BHARAT RAJ AND JINU MATHEW

Abstract: Gecko is the open source, free softwareweb browser layout engine used in all Mozilla-

branded software and its derivatives, including

later Netscape releases. Written in C++, Gecko is

designed to support open Internet standards.

Originally created by Netscape Communications

Corporation, its development is now overseen by

the Mozilla Foundation. Gecko offers a rich

programming API that makes it suitable for a

wide variety of roles in Internet enabled

applications, such as web browsers, content

presentation and client/server [1]. Primarily it is

used by Mozilla browser derivatives, such as

Mozilla Firefox, K-Meleon and Netscape, torender websites and the browser user interface

(written in XUL), but it is used elsewhere as well.

Gecko is cross-platform and works on a number

of different operating systems, including

Microsoft Windows, BSD s, GNU/Linux and Mac

OS X.Gecko is generally considered to be the

second most-popular layout engine on the Web,

after Trident (used by Internet Explorer for

Windows since version 4), and followed by

KHTML (used by Konqueror), WebCore (used by

Safari), Presto (used by Opera) and Tasman (used

by Internet Explorer for Mac).

Index Terms: Open source software, Mozilla firefox,Layout engine, Web browser

I. INTRODUCTION

Firefox is an open source cross-platform

web browser developed by the Mozilla Corporation.

Firefox has rich web browsing features which include

Tabbed Browsing,Spell Checking, Search

Suggestions, Session Restore, Web Feeds (RSS),

Live Titles,Integrated Search, Live Bookmarks, Pop-up Blocker, Streamlined Interface, and Accessibility.

This manuscript prepared by

*Guide, Faculty Department of Computer Science and

Engineering, Sahrdaya College of Engineering & Technology,

Kodakara.**Final year student, Department of Computer Science and

Engineering, Sahrdaya College of Engineering & Technology,

Kodakara.

Another important feature of Firefox is that it can becustomized by extensions, themes, and advanced

preferences. Firefox is built on top of Mozillasapplication platform and reusable components. For

example, the Firefox project is built on Gecko which

is also used in other Mozilla projects, such as

Camino.

The conceptual architecture of Mozilla

Firefox is developed based on the reference

architecture of Mozilla browser. The reference

architecture of Mozilla browser (see Figure 1.) shows

fundamental subsystems and relationships between

them. Mozilla Firefox fundamental subsystemsinclude User Interface, Browser Engine, Rendering

Engine, Networking, XML Parser, JavaScript

Interpreter, and Data Persistence. User Interface is

the layer between the user and the browser. The web

addresses are sent to the Browser Engine. Browser

Engine and Rendering Engine read web contents

which are written in languages like HTML, CSS,JavaScrip, and then render it and display it to the

user.

Fig.1: Reference Architecture of Mozilla Browser


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In Firefox conceptual architecture, the

layout engine is called Gecko. Gecko itself is a

browser engine, as well as a rendering engine. It talks

to other components, such as networking, XML

Parser, and so on. Figure 1 shows that the DisplayBackend is composed of GTK+ Adapter and GTK+ /

X11 Libraries. This is a specific Mozilla applicationwhich is running on Linux operating system. Mozilla

Firefox is a crossplatform browser.

Fig. 2: Conceptual Architecture of Mozilla Firefox

Geckois a layout engine currentlydeveloped by Mozilla Corporation, known as thelayout engine of the Firefox web browser, MozillaApplication Suite, Nvu, Mozilla

Thunderbird and many more. It is designed tosupport open Internet standards, and is used byapplications such as MozillaFirefox, Camino, Flock, Sea Monkey, K-Meleon, Netscape 9, Lunascapeand Epiphany to display web pages and, insome cases, an application's user interface itself(by rendering XUL). Gecko offers a rich

programming API that makes it suitable for a widevariety of roles in Internet-enabled applications, such

as web browsers, content presentation, and

client/server.Development originatedwith Netscape CommunicationsCorporation, but soon moved to the MozillaFoundation for the Mozilla application suite,and now used in many applications developed byMozilla Foundation and or the MozillaCorporation, as well as many other open sourcesoftware projects. It was also used in

laterNetscape Navigator releases.

Gecko is written in C++ and is cross-platform, and runs on various operatingsystems including BSDs, Linux, Mac OS

X, Solaris, OS/2,AIX, OpenVMS,and Microsoft Windows. Its development is nowoverseen by the Mozilla Foundation. Licensed by

a tri-licenseof the Mozilla PublicLicense (MPL), GNU General PublicLicense (GPL) and GNU Lesser General

Public License (LGPL), Gecko is free andopen source software.

Gecko is the second most-popular layout

engine on the World Wide Web,afterTrident (used by Internet Explorer forWindows since version 4), and followed

by WebKit (used by Safari & Google Chrome)and Presto (used by Opera).

II. USER INTERFACE

The User Interface (UI) of the Mozilla

browser (Firefox 2.0) is one major layer between the

users and the browser/rendering engine (GECKO). It

provides various features such as bookmarking web

pages, setting internet preferences, visualizing web

pages, and downloading files, etc.

The User Interface is split over two

subsystems allowing for parts of it to be reused in

other applications in the Mozilla suite such as the

mail/news client. Mozillas Cross-Platform Front End(XPFE) is a development environment based upon

XUL to make Mozilla applications like Firefox or

Thunderbird.

Fig. 3: User Interface Conceptual Architecture

The whole XPFE framework is made up of

the following parts:

1. XUL - xml language that describes the user

interface

2. CSS used for customizing or decorating the

user interface

3. JavaScript used for linking andprogramming the interface components

4. XBL(eXtensible Binding Language)

defines re-useable XUL components


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5. XPCom/XPConnect interfaces XPFE with

binary code (C/C++, etc)

6. XUL templates framework for importing

data


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7. RDF (resource description framework)

retrieves and stores data

8. DTD foreign localization

9. XPInstall standard installer for XPFE

applications

Most components in Firefoxs UI are createdby using XUL and HTML 4.0 and are decorated by

CSS1 and CSS2. XUL stands for XML User

Interface Language which is supported by Gecko, the

core browser/rendering engine of Firefox 2.0. XUL is

a Mozillas XML-based technology that allows users

to customize the existing interface components orcreate different types of cross-platform user

interfaces that connect or disconnect from the

internet. (Mixture of HTML, CSS, JavaScript, and

XML)

XUL provides users abilities to create the

following user interface elements:

Toolbars with buttons or other content

Menus on a menu bar or pop up menus

Tabbed dialogs

Trees for hierarchical or tabular information

Keyboard shortcuts

The User Interface interacts with Gecko,

which is the heart of the Mozilla framework.Gecko is

cross-platform browser/rendering engine that is used by Mozilla for interpreting and displaying web

content. The user interface elements are created and

defined in XUL and rendered by Gecko.

III. GECKO

Gecko is Firefoxs rendering and layout

engine. It is responsible for parsing and rendering

HTML and XML documents, as well as the XUL-

defined user interface. Gecko is comprised of the

following components:

HTML Parsers:

This component is responsible for parsing

HTML documents.

Content Model:

The content model arranges parsed

document data into a tree structure based on

the Document Object Model (DOM). Callsto any of the DOM APIs will modify the

Content Model.

Style System:

The Style System is responsible for parsing

CSS data.

Image Loader:

This component loads image data.

Frame System:

This component places the Content Models

DOM elements into frames, and uses theStyle Systems style information to calculate

the size of each frame. This size informationis used to arrange the frames into a new tree

whose structure represents the visual layout

of document. Items in the Frame Tree retain

pointers to their corresponding items in the

Content Model, so any change to the

Content Model will also produce change inthe Frame Tree.

Graphics Interface:

Gecko contains a platform-specific interface

for instructing the native OS to draw

information on the screen.

Fig. 4: Gecko Conceptual Architecture

IV. DATA FLOW INSIDE GECKO

HTML data comes into Gecko either from

the network or a local source. The first thing that

happens is that it is parsed, using Gecko's own

HTML parser. Then the Content Model arranges thisparsed data into a large tree. The tree is also known

as the "Document" and its structure is based on the

W3C Document Object Model. Any use of DOMAPIs manipulates the data in the Content Model.


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Next the data is put into frames using CSS

and the Frame Constructor. A frame in this sense

(which is not the same thing as an HTML frame) is

basically an abstract box within which a DOM

element will be displayed. This process produces a


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Frame Tree, which, like the Content Model, is a tree

of data, but this time focused not on the logical

relationship among the elements but on the

underlying calculations needed to display the data. In

the beginning a frame has no size. Using CSS rulesspecifying how the elements of the DOM should look

when they are displayed, including information likefont type or image size, the eventual size of each

frame is calculated. Because the same data may need

to be displayed in different ways -- to a monitor and

to a printer, for example -- a particular Content

Model may have more than one Frame Tree

associated with it. In such a case, each individualFrame Tree would belong to a different

"presentation" mode.

Fig. 5: Data flow within Gecko

Calculations continue as new informationflows into the system using a process called reflow.

As information in the Frame Tree changes, the

section of the Frame Tree involved is marked "dirty"

by the Frame Constructor. Reflow repeatedly steps

through the tree, processing every "dirty" item it

encounters until all the items it encounters are

"clean". Every item in the Frame Tree has a pointer

back to its corresponding item in the Content Model.

A change in the Content Model, say through using

the DOM APIs to change an element from hidden tovisible, produces an equivalent change in the Frame

Tree. It's important to note that all of these operationsare purely data manipulations. Painting to the display

itself is not yet involved at this point.

The next stage is the View Manager. With a

few small exceptions that have to do with promptingthe Frame Constructor to load graphics, the View

Manager is the first place in the process that accesses

the native OS. Delaying OS access until this point

both helps Gecko to run more quickly and makes

cross-platform issues easier to deal with. The View

Manger is the place where Gecko figures out where

on the display the data will need to be drawn. It then

tells the system that that area is "invalid" and needs tobe repainted. The actual painting is managed by the

gfx sub module, while other low-level systemoperations are run through the widget sub module,

which handles things like platform specific event

(mouse clicks and so forth) processing loops and

accessing system defaults (colors, fonts, etc.) Both

gfx and widget are system specific.

V. COMPARISON OF LAYOUT ENGINES

The following tables compare general andtechnical information for a number of layout engines.

Table 1: General Information

Engine Creator Softwar

e

license

Leading

application

Gecko Netscape/

MozillaFoundatio

n

MPL/G

NUGPL/G

NU

LGPL tr

i-license

Mozilla

Firefox

GtkHTML

(Based onKHTML)

GNOME GNU

LGPL

Novell

Evolution

iCab Alexander

Clauss

Propriet

ary

iCab

KHTML KDE GNU

LGPL

Konqueror

Presto Opera

Software

Propriet

ar

Opera

Prince

XML

YesLogic

Pty Ltd

Propriet

ary

Prince

XML

Robin Ritlabs Propriet The Bat!

Tasman Microsoft Propriet

ar

Microsoft

Entoura eTrident Microsoft Propriet

ary

Internet

Explorer

WebKit (B

ased on

KHTML)

WebKit

Foundatio

n

GNU

LGPL,

BSD-style

Safari, Goo

gle Chrome
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Table 2: Release History

Engine

Firstpublic

release

Firststablerelease

Lateststablerelease

Date

Versi

on

Dat

e

Ver

sion Date

Versio

n

Gecko

December7,199

8

"Preview"

March

19,1999

M3June11, 2009

1.9.0.11

GtkHTML

2000 ? 2000 ?

January

14,2008

3.17.5

iCab 1998 ? 1998 ?

January

1,2008

3.0.5

KHTML

October

2000?

October

2000?

May6, 2009

4.2.3

Presto

November13,20

02

7.0beta

1

January28,2003

7.0

March

3, 2009

2.2.2

Prince

XML

April,2003

1.0April

,2003

1.0Janua

ry,2008

6.0

Robin

April27, 2000

1.32April27, 2000

1.32

December27,20

06

3.95

Tasman

March

27, 2000

0

March

27,2000

0May11, 2004

1.0

Trident

April1997

IOctober

1997I

March

19, 2009

4.0

WebKit

January

7, 2003

48June23, 2003

85 -SVN versiononly

Operating System Support

The operating systems theengines can run on without emulation.

Table 3: Operating System support

Engin

e

Windo

ws

Mac

OSX

Linux BSD Unix

GeckoYes Yes Yes Yes Yes

GtkHTML

Yes Yes Yes Yes Yes

iCab NoTerminated(3.03)

No No No

KHTML

Yes Yes Yes Yes Yes

Presto Yes Yes Yes Yes Yes

Prince XML

Yes Yes Yes Yes No

Robin Yes No No No No

Tasman

No Yes No No No

Trident

YesDropped(4.0)

No NoDropped(5.0)

WebK

it

Yes Yes Yes Yes Yes

Although dropped in current version, older

versions of the Gecko layout engine for Mac

OS 9 are still available for download from

Netscape's Archived Products site.

Most of WebKit runs natively on Windows,

Safari 3.1 provides support for previously non-

ported features such as SVG, Canvas, andplugins.

VI. ADVANTAGES

Gecko is the smart embedding choice. It is

quick, robust, and highly standards compliant. In its

Mozilla and Netscape incarnations, it has been

widely distributed and very well reviewed.

It is Open Source. Unlike other embeddingchoices, all of Gecko's source code is freely available
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and fully customizable. You can tinker and tweak as

much as you need. Yet, depending on the license

chosen, it is quite possible to use Gecko as a

component in what is otherwise a fully proprietary

commercial product.

Because Gecko is associated with theMozilla project, there are many resources available to

assist the embedding effort. The Mozilla web site,

has an embedding project area. There is a newsgroup,

mozilla.dev.embedding, focussed on exchanging

information amongembedders, as well as a numberof other related newsgroups. A complete cross-

reference for the codebase is available, and filing,

following the progress of, and helping to fix any bugs

is made simple through the Bugzilla bug database.

Gecko is also architected from the ground

up to be cross-platform. Directly from mozilla.org, it

runs on Wintel, Mac OS 9.0 and OS X, and Linux,

and there are third-party ports to a number of other

platforms.

Finally, licensing Gecko is royalty-free,even if the final application is an otherwise

proprietary commercial product.Verygenerally, any

modifications of the original Mozilla-supplied source

code (but not the code in which it is embedded) must

be returned to the community, that same original

code must be made available to the application's

users (often by a link to the mozilla.org website), andthe application must indicate in some obvious way(for example, a logo on the box or on the About:

page) that the product embeds Gecko. Exact

descriptions of the possible licensing arrangements

are presented atMozilla & Netscape Public Licenses,

which is the only legally complete source for

licensing information.

VII.CONCLUSION

Gecko provides access to the Web via NFS,

allowing Web pages to be named, accessed, andcached as are Unix files. Standard Unix applications

such ascat and grep can be used to manipulate pages,

eliminating the need for new "Web aware"

applications. NFS provides cache consistency

between clients and the Gecko server, ensuring that

all applications using Gecko system see the same

version of a page. NFS also improves the

performance of accessing pages on the Gecko server.Pages are automatically cached on the client, and

name lookup results are cached for subsequent

lookups, significantly improving their performance.

The use of UDP vs TCP to transfer pages enables

Gecko to transfer a 16KB page between the server

and client 6.5 times faster than HTTP.

REFERENCES

[l] Scott Baker and John H. Hartman, The Gecko NFS Web

Proxy, Department of Computer Science, The University of

Arizona, Tucson, AZ 85721.

[2] Siwat Saibua, Richard A. Aukerman, Joon-Yeoul Oh,Internet

explorer and firefox:web browser features comparision and

their future,texas a&m university-kingsville.