WebGL入门指南：Tony Parisi的2012最新教程

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to Christell Gause, head of support at TurboSquid, for his diligent efforts in helping me

btain permission from the many TurboSquid artists whose content is featured here.

Also, I could not have created the examples for this book without additional help

and/or contributed content from data junkie Theo Armour, 3D programming ace Don

Olmstead, and 3D artist Arefin Mohiuddin of Sunglass.io.

WebGL is blessed to have a strong community of developers. I would like to thank the

three.js developers, including guru Ricardo Cabello (“Mr.doob”) and contributors Bra

nislav Ulicny (“AlteredQualia”) and Tim Knip, for their patience with my often-naïve

uestions and their overall enthusiasm for the project. I owe an eternal debt of gratitude

to Ken Russell, the WebGL working group chair and WebGL development lead at Goo

gle. Ken has not only built a great product, but he kindly agreed to write the foreword

or this book.

Finally, I would like to thank my friends and family. Mark Pesce, my old VRML partner

in cr

ime, is a veteran author. His commitment to excellence in writing and his passion

for emerging technology have been a constant source of inspiration to me over the years.

Many thanks to my buddy and sometimes-business-partner Scott Foe, who was always

supportive of this book, despite the major distraction it created from our day-to-day

startup. Last but not least, my family provided the moral support, patience, and loving

environment that any author needs to thrive. More than that, they pitched in on the

logistics: my 10-year-old, Lucian, gets props for play-testing most of the examples in the

book, and my wife, Marina, kept me honest with art direction so that my cobbled-

together examples would at least have a consistent look and coherent story.

xiv | Preface

WebGL is the new standard for 3D graphics on the Web. With WebGL, developers can

harness the full power of the computer’s graphics rendering hardware using only Java

Script, a web browser, and a standard web technology stack. Before WebGL, developers

ad to rely on plug-ins or native applications and ask their users to download and install

custom software in order to deliver a true 3D experience.

WebGL is part of the HTML5 family of technologies. While not in the official specifi

cation, it is shipped with most browsers that support HTML5. Like Web Workers, Web

ockets, and other technologies outside the official W3C recommendations, WebGL is

an essential component in an emerging suite that is transforming the modern browser

into a first-class application platform.

WebGL works on the majority of desktops, as well as a growing number of mobile

browsers. There are millions of WebGL-enabled seats already installed, most likely in

cluding the machines you run at home and in your office. WebGL is at the center of a

ibrant and growing ecosystem that is making the web experience more visually rich

and engaging. There are hundreds of sites, applications, and tools being developed, with

applications ranging from games to data visualization, computer-aided design, and

consumer retail.

While the low-level nature of the WebGL API may appear daunting at first, there are

everal open source JavaScript toolkits that take the grunt work out of development. I

want to be careful not to oversell this—3D is still hard work—but these tools at least

make it possible for mere mortals with modest web development experience to get into

the WebGL business. So maybe it’s finally time for you to create that hit game you always

wanted to make. Or maybe today is the day when you blow your boss’s mind with a

dazzling intro graphic for your home page.

In this chapter, we will take a quick tour of the low-level underpinnings of WebGL to

ive you a foundation. For the majority of the book, we will use a high-level 3D toolkit,

Three.js, which hides many of the messy details. But it is important to know what these

tools are built upon, so let’s start by exploring WebGL’s core concepts and API.

WebGL—A Technical Definition

WebGL is developed and maintained by the Khronos Group, the standards body that

so governs OpenGL, COLLADA, and other specifications you may have heard of. Here

is the official description of WebGL, from the Khronos website:

WebGL is a royalty-free, cross-platform API that brings OpenGL ES 2.0 to the web as a

3D drawing context within HTML, exposed as low-level Document Object Model inter

faces. It uses the OpenGL shading language, GLSL ES, and can be cleanly combined with

ther web content that is layered on top or underneath the 3D content. It is ideally suited

for dynamic 3D web applications in the JavaScript programming language, and will be

fully integrated in leading web browsers.

2 | Chapter 1: An Introduction to WebGL

This definition comprises several core ideas. Let’s deconstruct them here:

WebGL is an API

WebGL is accessed exclusively through a set of JavaScript programming interfaces;

here are no accompanying tags like there are with HTML. 3D rendering in WebGL

is analogous to 2D drawing using the Canvas e

lement, in that it is all done through

JavaScript API calls. In fact, access to WebGL is provided using the existing Canvas

element and obtaining a special drawing context specific to WebGL.

WebGL is based on OpenGL ES 2.0

OpenGL ES is an adaption of the long-established 3D rendering standard OpenGL.

e “ES” stands for “embedded systems,” meaning that it has been tailored for use

in small computing devices, most notably phones and tablets. OpenGL ES is the

API that powers 3D graphics for the iPhone, the iPad, and Android phones and

tablets. . WebGL’s designers felt that, by basing the API on OpenGL ES’s small foot

print, delivering a consistent, cross-platform, cross-browser 3D API for the Web

ould be more achievable.

WebGL combines with other web content

WebGL layers on top of or underneath other page content. The 3D canvas can take

p just a portion of the page, or the whole page. It can reside inside <div> tags that

e z-ordered. This means that you develop your 3D graphics using WebGL, but all

your other elements are built using familiar old HTML. The browser composites

(combines) all of the graphics on the page into a seamless experience for the user.

WebGL is built for dynamic web applications

WebGL has been designed with web delivery in mind. WebGL starts with OpenGL

ES, b

ut it has been adapted with specific features that integrate well with web

browsers, work with the JavaScript language, and are friendly for web delivery.

WebGL is cross-platform

WebGL is capable of running on any operating system, on devices ranging from

hones and tablets to desktop computers.

WebGL is royalty-free

Like all open web specifications, WebGL is free to use. Nobody will be asking you

o pay royalties for the privilege.

The makers of

Chrome, Firefox, Safari, and Opera have committed significant resources

o developing and supporting WebGL, and engineers from these teams are also key

members of the working group that develops the specification. The WebGL specification

process is open to all Khronos members, and there are also mailing lists open to the

public. See Appendix A for mailing list information and other specification resources.

WebGL—A Technical Definition | 3

“Math is hard!”

—

Barbie

3D Graphics—A Primer

As sexist as the infamous quote may be, I have to say that whenever I code something

in 3D

, I, like Barbie, get a very strong urge to indulge in shop therapy. It’s hard stuff and

it often involves more than a little math. Luckily, you won’t have to be a math whiz to

build something in WebGL; we are going to use libraries that do most of the hard work

for us. But it is important to understand what’s going on under the hood, and to that

end, here is my attempt to summarize the entire discipline of interactive 3D graphics in

a few pages.

3D Coordinate Systems

3D drawing takes place, not surprisingly, in a

3D coordinate system. Anyone familiar

ith 2D Cartesian coordinate systems such as you find on graph paper, or in the window

coordinates of an HTML document, knows about

x an

y values. These 2D coordinates

def

ine where <div> tags are located on a page, or where the virtual “pen” or “brush”

draws in t

he case of the

HTML Canvas

element. Similarly, 3D drawing takes place in a

3D coordinate system, where there is an additional coordinate,

z, which describes depth

.e., how far into or out of the screen an object is drawn). The WebGL coordinate system

is arranged as depicted in

Figure 1-2, with x running horizontally left to right, y running

vertically bottom to top, and positive z coming out of the screen.

If you are already comfortable with the concept of the 2D coordinate system, I think the

ransition to a 3D coordinate system is pretty straightforward. However, from here on,

things get a little complicated.

Meshes, Polygons, and Vertices

While there are several ways to draw 3D graphics, by far the most common is to use a

mesh. A mesh is an object composed of one or more polygonal shapes, constructed out

vertices (x, y, z triples) defining coordinate positions in 3D space. The polygons most

ypically used in meshes are triangles (groups of three vertices) and quads (groups of

four vertices). 3D meshes are often referred to as

models.

Figure 1-3 illustrates a 3D mesh. The dark lines outline the quads that comprise the

esh, defining the shape of the face. (You would not see these lines in the final rendered

image; they are included for reference.) The

x, y, and z components of the mesh’s vertices

def

ine the shape

only; surface properties of the mesh, such as the color and shading, are

def

ined using additional attributes, as we will discuss shortly.

4 | Chapter 1: An Introduction to WebGL

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